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Q# 1: First of all I must congratulate you on a fantastic website; so informative. I am studying to become a Health Physics Monitor and have found your information very clear, simple to follow and very helpful indeed. I have a request regarding types of detectors and their uses, particularly the Thermoluminescent Detector/Dosimeter (TMD). Your description and information on the other types of monitors (for example the GM Tube/Scintillator) was excellent and broadened my understanding. Unless I have missed it I could not find that type of information regarding the TMD. Would it be possible to have this? (2/9/12)

Date: February 9, 2012

Answer: Thank you very much for the nice words about the Plexus-NSD web site. We’re glad you are finding some interesting things there, and we congratulate you on pursuing a career in the radiation protection field.

Your question about thermoluminescent dosimeters (TLD) is a good one, and you’re right! We don’t have a write-up on this topic on our web page. How could we have missed it? It looks like we have something new to add to the “to do” list.

In the meantime, let me at least give you a bit of information about TLD just to get you started on your research. TLD are inorganic crystals with impuritities chosen so that the electrons and holes remain trapped at the activator sites at room temperature. When placed into a radiation field, a TLD crystal serves as an integrating detector in which the number of trapped electrons and holes depends on its radiation exposure history. After the exposure takes place and the TLD material is heated, the trapped electrons and holes migrate and combine, with the accompanying emission of photos. If the heating occurs in a “TLD reader” the photons are picked up by a photomultiplier tube and converted into an electronic signal. The light yield as a function of heating temperature is that is used to interpret the amount of radiation to which the crystal has been exposed.

The terms “TLD-100” and “TLD-700H” are brand names given by suppliers of TLD for radiation measurement purposes. TLD-100 is natural lithium fluoride in the form LiF:Mg,Ti. TLD-700 is the same as TLD-100, but is enriched in Lithium-7. TLD-700H is in the form LiF:Mg,Cu,P, which has application for clinical dosimetry because of its improved reproducibility, linearity and energy response. In addition, it has an additional advantage of higher sensitivity, meaning it gives a higher response.

While we’re pulling together a little tutorial on TLD and other external radiation monitoring methods, let us refer you to some good references on the topic. For starters, Dr. Glenn Knoll’s book, “Radiation Detection and Measurement” gives some excellent information. A concise treatment of thermoluminescence in general can be found in Dr. James Turner’s book, “Atoms, Radiation and Radiation Protection”. There are also an excellent chapters on the topic in the proceedings of the Health Physics Society’s 1996 summer school, “Applications of New Technology: External Dosimetry” (see Chapter 6), and in the 2001 proceedings, “Radiation Instrumentation” (see Chapter 5). Finally, an “oldie but goodie” is a two-volume CRC Press publication entitled “Thermoluminescence and Thermoluminescent Dosimetry”. All of these publications can be found at your nearest university or technical library.

Q# 2: I am trying to determine the type of Sodium Iodide detector i need to buy for a project. I need to know how to determine how sensitive the unit has to be. I will be testing the activity of 15 micro liters and 30 micro liters of I-123. What amount of activity can I expect in Micro Curies for this amount of I-123? I will be filling 20 to 25 capsules a minute…would you happen to know what a typical response time for a Sodium Iodide detector is? (2/20/12)

Date: February 20, 2012

Answer: You’re not going to like this, but the answer to your question is “it depends”. Thallium-activated sodium iodide detectors, or NaI(Tl) detectors, if calibrated appropriately, can do a great job of quantifying Iodine-123 (I-123) in solution. This isotope emits a (primarily) 159 thousand electron volt (keV) photon during decay, which is readily detectable by most NaI(Tl) detectors, even if the concentrations are fairly low. However, the actual response of a specific detector type/configuration depends on so much more than just the radionuclide concentration.

Let’s take a look at a few things to see if we can’t at least get close to an answer for you. In the Tool Box section of the Plexus-NSD web page, you can see that the gamma ray dose constant for I-123 is 0.277 rem/hr per Curie at a distance of one meter from a point source. This proportion tells us that one microcurie of I-123 should deliver a radiation dose of 0.277 microrem per hour at the one-meter distance. (As you probably already know, the dose rate decreases by the inverse square of the distance between the detector and the source. This means the detector will give you the highest response when it is positioned as close as possible to those capsules of I-123. In fact, if we know the dose rate at one distance, we can calculate it for pretty much any other distance, although the calculation doesn’t hold up very well if the source is too close to the detector as other issues come into plan.)

Now that we have an approximate dose rate per microcurie, let’s pick out a detector. There are many manufacturers of sodium iodide detectors and we are definitely not recommending any one brand over another. But for talking purposes let’s visit the Ludlum Instruments web site at www.ludlums.com where we can find some information on a Model 44-10 detector. This is a 2-inch by 2-inch NaI(Tl) detector which gives an approximately response of 900 counts per minute (cpm) per microR per hour from Cesium-137 (Cs-137) photons (i.e., 662 keV in energy). Therefore, if we have a one microcurie I-123 source producing a dose rate of 0.277 microrem per hour at one meter, and if we put that detector one meter away from the source, we should see a response on the ratemeter of about 250 cpm.

Does that mean a Model 44-10 is best-suited for your job? No siree! The nominal background response of a Model 44-10 is about 9,750 counts per minute, meaning the 250 cpm expected count rate will likely be lost in the noise. Not only that, the response of NaI(Tl) detectors in general is influenced by the photon energy. It you look at the energy response curve for the Model 44-10, you can see that if it was calibrated with Cs-137 it will over-respond by quite a bit when in the presence of I-123.

Does that mean you should toss out the Model 44-10 for your purposes? No siree again! If you calibrate the detector and rate meter with a traceable standard of I-123, in the same counting geometry you will be using to assess activity in your capsules, and if you come up with a counting geometry that will maximize the response, and if you do your counting in a relatively low background area, and if you consider hooking your detector up to a scaler rather than a ratemeter (i.e., where counts are integrated over time), and if you optimize the counting time, that Model 44-10 just might do the trick!

The bottom line is that there are quite a number of variables associated with selecting the correct radiation detection instrument for a particular job. This means I can’t answer your question without knowing more about the instrument, its response, how it will be calibrated, how it will be used, where it will be used, and more. However, you now know that there is no such thing as a universal radiation detector. That alone puts you ahead of the crowd!

Q# 3: I am going to be working on a site that involves the cleanup of soil with 29 pCi/gram of Radium 226. My question is how to take that information and express the potential for exposure in REM/year or miliREM/year? (3/7/12)

Date: March 7, 2012

Answer: Your question is a good one that deserves a solid answer. Unfortunately, it is often a question that confuses people that are not fully comfortable with radiation-related quantities and units. Before we get to your answer, let’s go through a few pertinent definitions.

The “activity” of a radionuclide refers to the number of stable atoms present and the rate at which they are decaying. The units used to describe radioactivity are “curies”, “millicuries”, etc. As you noted in your question, the activity is distributed in soil in a measured concentration of picocuries (pCi) of radioactivity per gram of soil. As these atoms decay, they emit “radiations”. The “absorbed dose” is the amount of radiation energy deposited in matter as a result of the activity (or decay) of the radionuclide. In fact, the unit “rads” is initials meaning “radiation absorbed dose”. Converting an activity concentration of pCi/g to radiation dose in rads or rems (or a smaller unit, millirems) in a year needs some assumptions on how the material will be handled, by what pathways an individual will be exposed, how long they will be exposed, and more.

Now let’s move on to your specific question. You know that at your site, Radium-226 is present in a presumably mean concentration of 29 pCi/gram. However, you didn’t tell me if other isotopes are present. I happen to know that, in nature, Radium-226 is a series radionuclide with radioactive progeny, and it is also a progeny of another series radionuclide, Uranium-238. Unless you tell me otherwise, I would have to presume the decay progeny of uranium and radium are also present in the soil.

The radiation dose associated with working with/on/near soil like this, calculated in units of millirem, requires knowledge of if and how the radioactivity in the soil becomes airborne (i.e., resuspension factors), whether it is available for ingestion, particle sizes, solubility factors, inhalation/ingestion duration, and the selection of appropriate factors for converting radioactivity inhaled or ingested into dose. Of course, this needs to be done for all of the isotopes present (i.e., parents and progeny). In addition, the external dose rate from the radioactivity that is presumably laying on the ground with the individual standing on top of it, needs to be determined by taking into account the individual’s time and motion with respect to the radioactivity source. I don’t have nearly enough information to make these calculations for you, meaning any dose estimates I would put forth would be pure speculation.

The site safety officer for your project, or your corporate health and safety officer should have prepared a site-specific assessment of the radiological risks of the work you will be performing. It is also important to note that regulators, both Agreement States and the U.S. Nuclear Regulatory Commission, require individuals be monitored for radiation exposure if the results of the risk assessment show there is a potential to exceed 10% of the allowable dose limit. Depending on circumstances, there may also be a State requirement for licensing before work at this site can proceed. I apologize for leaving you with more questions than answers, but like I said at the start of my response, your question is a good one and it deserves a solid answer.

Q# 4: What is the differences between high mA and low Time and High Time and low mA setting (while mAs is constant) on tube life? what is the defferences between low kvp and high kvp on tube life? I think using the low mA and long time extend the tube life because at long time the fewer number of electrons strike to anode so the anode life extends but I cant understand How this condition effects on filament life because at this condition(low mA and long Time) the fillament power is constant. also,at this condition(low mA and long Time) the uniformity of striked electrons to anode is less and consequently the output X-ray beam from anode is less uniform. Is this consequence correct or not? what’s your idea? also,I think the high Kvp w.r.t low kvp extends the tube life because using the higher kvp decreses the photoelectric effect and generated heat on housing so the anode warm sooner. but on the other hand,using the higher kvp increases the energy of electrons striking to anode and these high energy electrons increase the propability of anode cracking,also the using hte higher kvp increases the heel effect and nonuniformity of output X-ray beam. Is this consequence correct or not? What’s your idea? (3/26/12)

Date: March 26, 2012

Answer: As you probably already know, there are many factors that degrade the life of a x-ray tube, all of which are related to the design and materials of construction. Therefore, the best response to your question will come from whomever manufactured the tube you are using.

Some manufacturers report that the limiting factor on tube life is the filament and not the. Consequently, the life of the tube can be extended if currents (mAs) are applied sparingly. (During operations, the surface of the filament is vaporized in order to provide the electrons used to bombard the target, resulting mostly in the generation of heat and a few x-rays.) Maintaining maximum current if lesser currents will produce satisfactory results will not only shorten the filament life, but it will lead to unstable operation as evaporated tungsten from the filament is deposited on the glass envelope of the tube. Therefore, if you select lower currents and longer exposure times in order to achieve the desired exposure rate, you might get more life out of your tube.

On the other hand, the tube target can also play a limiting role. The design and materials of construction for the target are usually selected to best manage the heat that is generated during use. The life of the target can be preserved by letting it “warm up” before performing operations at elevated mAs. Uneven expansion caused by thermal stress can crack the target, rendering it less useful. Therefore, following recommended warm-up procedures at the start of the work day, and then following them again if the tube is “idle” for a long enough period of time, will also go a long way in extending tube life.

On a final note, operating your machine beyond the manufacturer’s specified ratings can result in premature target ware, etching of the target or even melting. Etching results in a reduction to the radiation output because electrons from the filament strike crevices and are absorbed in the surrounding target material. Severe etching might even result in gases being liberated from the target material which again results in tube instability. Excessive heat transfer from the target into the rotor body can cause bearing failure or slow rotation, which also increases the target temperature. We hope this helps!

Q# 5: I am a mom of a beautiful healthy one month old baby boy. Before I got pregnant I had a car accident and my chiropractor ordered X-rays . They did 4 lumbar, 4 cervicals, 2 torax on June 25, 2011 They did not provide me any shield to cover my reproductive organs. My ovaries were exposed to radiation. On August 24 I found out I was pregnant with 4 weeks. I was not pregnant at the time of the X-rays I got pregnant in the next cycle. I have heard scary things about X-rays including that they can cause cancer (leukemia) in children. My baby is healthy with no genetic disorders but I want to know if he is at risk to develop leukemia due to the X-rays that I had before I conceived him. (5/31/12)

Date: May 31, 2012

Answer: First off, congratulations on the birth of your new son! Before I go any further into your question, let me first reassure you that the medical procedures you described in your question pose no risk to the little guy. Let me tell you why.

First, here is a bit of information about x-rays. They constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics”section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

Diagnostic x-rays for medical and dental purposes are still probably the most commonly employed form of radiology, a science that generally speaking, uses imaging techniques to allow doctors to see inside a patient’s body. Examples in addition to x-rays include angiography, breast imaging (mammogram), computerized tomography (CT) or “CAT Scans”, magnetic resonance imaging (MRI), nuclear medicine procedures, and ultrasound. Fluoroscopy is another diagnostic tool used routinely by medical professionals. In contrast to x-rays, which provide a “snapshot” similar to using a camera, fluoroscopy procedures are “dynamic” in nature and provide a “video” which captures motion.

Generally speaking, the amount of radiation exposure a patient receives during procedures like you described is trivial in light of the amount needed to result in demonstrable radiation-related health effects. If you check out the listing on the Plexus-NSD web site (see http://www.iem-inc.com/toolexpo.html and then scroll down to “radiographic procedures”, you can see that the types of x-rays you received delivered a dose of about 1,000 millirem, give or take. There has never been a demonstrable health effect associated with radiation exposures of 10,000 millirem or less. And even for acute exposures between 10,000 and 50,000 millirem, the effects are typically small and reversible. (By acute, I mean instantaneously, not over a period of time. As the exposure duration increases, the body’s ability to repair increases, raising the threshold at which effects can be seen.) It takes very high radiation exposures, much higher than the types you have described for there to be any increased risk of effects (i.e., cancer) above the normal population incidence.

During certain stages of development, the embryo/fetus is believed to be more sensitive to radiation damage than adults. If you look around you when you visit your radiologist’s office, you will very likely see a number of signs posted in various areas asking you to tell your technician or the physician if you think you are pregnant. In addition, many facilities require each female patient to respond to the “are you or do you think you might be pregnant” question before proceeding further with the procedure. Again, this is to avoid unnecessary radiation exposure for the developing fetus. However, there are times when the life and well-being of both the mother and the unborn child would be jeopardized if the x-ray or other radiation-related procedure did not occur. In that case, the physician typically weighs the pros and cons, then advises the patient accordingly.

Radiation-related health effects on the developing fetus are dependent upon the magnitude of the total dose, and on the dose rate. In general, they are no different than radiation-related health effects in all humans. In the case of your boy, he was not conceived until after you received your diagnostic procedures, so he has no additional risk.

If you would like to learn more about the issue of diagnostic radiology and pregnant females, I suggest you visit the “Radioactivity Basics” section of the Plexus-NSD web site. In addition, you might try to locate a copy of a National Council on Radiation Protection and Measurements (NCRP) Report No. 105, Radiation Protection for Medical and Allied Health Personnel. (Try visiting a local technical or university library.) In addition, the National Academy of Sciences, in its series of reports entitled “The Biological Effects of Ionizing Radiation” discusses fetal and terratogenic effects of radiation exposure. Finally, be sure to discuss this situation with your radiologist. He or she can give you information that is specific to your case. In the meantime, we at Plexus-NSD send our best to you and your new baby boy.

Q# 6: How do you relate 4.2E-12 atom % of tritium to microCuries/cc of tritium? (6/18/12)

Date: June 18, 2012

Answer: Your question is a bit difficult to answer without without knowing more about the rest of the compound. Without that information, we will have trouble coming up with a density so we can go from mass to concentration. Let’s assume, for a minute that you have given us a weight percent instead of an atomic percent. In this case, your compound would have 4.2E-12 grams of tritium in it, for every gram of compound. Let’s also assume the compound is water, meaning the density is one gram per cubic centimeter. We can look up the specific activity of tritiated water (i.e., Hydrogen-3) on the Plexus-NSD web site (go to http://www.iem-inc.com/toolspa.html and then scroll down to “Hydrogen”). With that, we have everything we need in order to perform the calculation. The hard part is trying to type it into an e-mail which isn’t the most equation-friendly way of getting our point across:

(4.2E-12 g H-3/g compound) * (7.7E3 Ci H-3/g H-3) * (1E6 microCi/Ci) * (1 g/ cc) = 3.2E-2 microCi/cc = 0.03 microCi/cc

Hopefully you can take this little example, along with the specifics of your compound, to come up with the correct concentration. Good luck!

Q# 7: Is there anything wrong with marking an Exempt (does not meet criteria of both columns in Curries, in 49 CFR 173.436) radioactive shipment as an Excepted Quantity shipment since the consignment exceeds Curries per consignment? (7/30/12)

Date: July 30, 2012

Answer: If we understand your question correctly, it’s a good one. However, not a one of us CHPs at Plexus-NSD have the special skills needed to interpret and understand those pesky transportation regulations. Because Plexus-NSD’s Nuclear Services Division is in the best position to give practical guidance, I forwarded your question to that group and one of them kindly provided me with an answer.

While what you are wanting to do is not illegal or a departure from the regulations from a radiological standpoint, our crack shipper thinks you may be making things a lot harder on yourself than necessary. First they pointed me to a few definitions to help make their case.

According to the DOT, an item is considered to be “exempt” from their rules for shipping radioactivity if it does not meet the criteria laid out in 49 CFR 173.436. In other words, the item is not considered to be radioactive material so long as its activity does not exceed the limits shown in the 10 CFR 173.435 table. Also according to the DOT, “radioactive material” is any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed the values specified in 49 CFR 173.436, or values derived by the methodology outlined in 49 CFR 173.433.

Moving now to “excepted quantities”, the DOT agrees that these could very well be below the levels in 49 CFR 173.435, but they can exceed the values in 49 CFR 173.436. Therefore, items in this category are considered to be “radioactive” and are thus subject to the applicable marking, packaging, and manifesting requirements. Our crack shipper thus recommends that, to avoid the need for marking, packaging and manifesting, you avoid marking a package or consignment as radioactive unless it actually meets the DOT definition of radioactive.

Q# 8: Working level monitors are all about collecting and detecting. Which 2 isotopes are counted when the filter paper is analyzed? (8/28/12)

Date: August 28, 2012

Answer: There a number of ways to evaluate the concentration of radon (Radon-222 or Rn-222) gas in air, and each has advantages and disadvantages. A Working Level Monitor draws ambient air through a filter designed to trap airborne dust. An alpha detector is then used to count the alpha emissions from the filter that occur while the radon progeny on the dust decay. The energy of the alpha particles released ranges from two (2) to eight (8) million electron volts, or MeV. The alpha activity detected is directly proportional to the number of alpha particles emitted by the dust, and must then be converted to Working Level (WL) values.

Sounds simple, right? Well it is . . . sort of. Let’s assume the radiation detector has been properly calibrated and that the measurement results are taking into account self-absorption as well as detector efficiency. The results obtained from a Working Level Monitor then need to be interpreted in light of the assumed equilibrium factor between the radon progeny and the radon gas. As you probably already know, the definition of a Working Level is “any combination of short-lived radon decay products in one liter of air that will result in the ultimate emission of 1.3 x 105 MeV of potential alpha energy.” This intensity of alpha radiation is equivalent to the alpha energy released by 100 picocuries per liter of Rn-222 with all decay products in equilibrium.

However, since Rn-222 is a gas, and the Working Level Monitor is measuring alpha activity from dust particles, that assumption of equilibrium is critical. What’s more, the radon decay products are seldom actually in equilibrium due to variations in ventilation, static electricity and total suspended dust in the room or building being assessed. Generally speaking, an assumed equilibrium ratio is 0.5 (i.e., the progeny are halfway toward equilibrium) is typical for most systems, which means one measured Working Level is actually equivalent to 200 picocuries of Rn-222 per liter. In reality, they vary with time and measurement location and ratios ranging from 0.3 to 0.7 are not atypical. Large building and rooms often exhibit equilibrium ratios of less than 0.05.

You might want to take a look at the measurement guidelines offered by the U. S. Environmental Protection Agency (EPA) for the collection and detection of radon progeny. Specifically, check out the EPA’s 1986 publication entitled “Interim Indoor Radon and Radon Decay Product Measurement Protocols” (Report No. PB86-2215258). Another good one is the 1993 publication entitled “Protocols for Radon and Radon Decay Product Measurements in Homes” (Report No. EPA 402-R-92-003). Both of these documents, available on the EPAs web site at www.epa.gov have useful information on the use of and interpretation of data from Working Level Monitors such that the results are consistent and defensible.

Q# 9: We have a rather large geological/mineral collection and have found a number of radioactive specimens. The museum is in the process of identifying the specimens and want to store ‘hot rocks’ in a separate air-tight cabinet and store it away from work areas. Some of the samples are fairly elevated. With storing these samples in a cabinet, radon gas will be an issue so we are looking to vent the cabinet to the outside. We will have to fabricate the ventilation system to add to the cabinet- have you heard of a project similar to this? Do you know anyone who could be contacted? We have a mechanical engineer and Industrial hygienist evaluating but thought I would ask Plexus-NSD. Our concerns with these rocks are exposure control, security of collection and the radon. Anything else to think about???? Thanks so much for any assistance. (10/28/12)

Date: October 28, 2012

Answer: We’ve seen quite a number of uranium-bearing rock collections in local museums and universities, but in all cases they were displayed in the same cases as other rocks (i.e., none of them were air-tight). Before going to a lot of trouble and expense, have you determined the radon emanation rate from the rocks? Depending on the matrix, and taking into account the fact that only radon atoms produced in the outer surface will make their way to a release point before they decay into their particulate progeny, it may be that radon isn’t really an issue for the rocks in question.

If it turns out radon mitigation in the display cases is necessary, ventilation is generally easier to implement than a technique like electrostatic elimination. For controlling external exposures, don’t forget the time-honored methods of “time”, “distance” and “shielding”. Security is another topic entirely that us CHP’s leave to the professionals.

Don’t forget that when it comes to sources of radioactivity, whether they are sealed radiation sources, bulk materials or mineral collections, it all comes down to dose. A simple pathways analysis based upon reasonable use scenarios and with the radiological constituents known to be in your rock collection should quickly identify the exposure pathways that will require control. If the dose potential from a pathway is not distinguishable from background, then no need to implement a protection mechanism. If it is, then that is where your efforts should be focused.

All of us at Plexus-NSD wish you luck in dealing with your mineral collection. We applaud your efforts to address potential safety and security issues in advance of gathering all of the “hot rocks” into one location!

Q# 10: I just had a scary episode at the dentist with the blue curing light. I had my two front teeth bonded. The girl assisting the dentist applied (pressed) the blue curing light directly against/onto my teeth several times (in the front and back of my teeth/mouth), rather than keeping some space or distance between the end of the light and my teeth. I didn’t feel any heat, but I did feel extreme vibrations and a weird sensation on my teeth and in my mouth. She did this several times for several seconds The dentist even told her she should keep it in mid-aid, not against my teeth. Could any health affects happen here like cancer? (11/13/12)

Date: November 13, 2012

Answer: During your visit to the dentist, the hygienist was using a light source to cure the composite material used in the bonding process. If the composite material is not cured correctly, it may not have a very long lifetime, so curing is a good thing.

According to an article published in a journal “Inside Dentistry” by Dr. Eduardo Mahn, says that there are four possible types of light that may be used for material curing, but the most common is a “light-emitting diode” or LED, capable of curing composites with a range of depth, compressive and flexural strength. The LED delivers visible light with a wavelength of approximately 410 nanometers.

In his article, Dr. Mahn explained that the amount of time required to cure the composite material is variable and each dentist needs to adjust their technique to match the manner in which the composite was applied and blended. Not only that, every manufacturer of the light sources designs their devices differently depending on use. For example, a different light intensity is used if the probe is applied directly to the tooth versus being spaced a few millimeters from the surface of the composite material. Dr. Mahn also explained that the advantage of a space between the light and the composite surface is to illuminate a wider area and thus achieve a more even curing.

The bottom line is that this visible light treatment results in polymerizing the composite material so that it will become hard or require replacement any time soon. The technique used by the technician was not a safety issue to you as there are no health effects associated with the light source, although sometimes these sources are shielded to protect the eyes of the technician (i.e., sun glasses!). The dentist did the right thing by giving her instruction in the proper use of the light source as the proper technique is as important as the selection of the correct composite to ensure your teeth are bonded appropriately. In case you’re interested, here is a reference to Dr. Mahn’s paper: Reference. Mahn, E. (2011). “Light Polymerization”, Inside Dentistry, Volume 7, Issue 2, February, 2011.

Q# 11: Our office has recently been assisting our museum go through rock specimens and have found quite a lot of radioactive rocks containing Uraninite and other radioactive minerals. These samples are being bagged and will be stored in a separate cabinet that will be vented to prevent radon build-up. We also we ‘lucky’ enough to find a few surprises…. We found a few samples with ‘yellowcake’ that have been stored for a very long time in a basement. What would be the proper method to dispose of these samples? One of the sample containers appears to be leaking. We have bagged the samples to prevent any additional spillage. Other challenging items found included samples of soil from the underground testing of nuclear explosions that occurred in 1962 and 1968 from the Nevada test site. I have contacted the State of Nevada and the DOE of that area. Any suggestions on what to do with those? The fallout isotopes of Cs and Co will generally have gone through at least one half-life. Have no idea what other isotopes may be in there…. (11/29/12)

Date: November 29, 2012

Answer: To dispose of your interesting collection, you might want to start first with the company that handles all of your hazardous waste disposal. Many of these firms have an option for disposal using a local landfill or at least a nearby state facility. The disposal of licensed radioactive materials is more difficult (and more expensive!), but its sounds as if your sample of yellowcake meets the limited quantities established by the U. S. Nuclear Regulatory Commission in 10 CFR 40.13 and/or 10 CFR 40.22. If your HazMat carrier can’t help you out, you can always contact a firm licensed to handle radioactive materials but be prepared to open your wallet! You might want to give your State bureau of radiation protection a call to see if they have any thoughts, suggestions or recommendations.

Your samples from the Nevada Test Site that date back to the 1960’s could very likely contain Cesium-137 (half-life of 30 years) and Cobalt-60 (half-life of five years). Another higher-yield fission product that could still be hanging around is Strontium-90 (half-life of 29 years). The many and various other isotopes created as part of the fission process have half-lives of less than a year and are probably long gone by now.

Good luck with your display. There are many reasons why it would be great if you could keep the samples, but that decision should be made after you have a good understanding of what you need to do to keep your employees and visitors to the museum safe. You’re on the right track!

Q# 12: As lab manager for a well water testing company in a ‘hot zone’, I have seen some very elevated levels of radioactivity. I’ve personally seen well water gross alpha as high as 8,180 pCi/l, gross beta at 1,170 pCi/l, radon @ 177,000 pCi/l & uranium at 6,000 ug/l. Are you aware of any calculator(s) that can convert radioactivity in water into laymen’s terms? I’d like to know what the equivalent exposure in chest x-rays is, for example. (12/13/12)

Date: December 13, 2012

Answer: Welcome to the world of natural radioactivity! You aren’t the first person to identify elevated concentrations of uranium and radium in water samples and I can assure you won’t be the last. Some of us here at Plexus-NSD very recently did an evaluation of a well water and drinking water supply only to identify concentrations that make yours seem pale by comparison.

Converting radionuclide concentrations in water, food or anything else that a human might consume is relatively straight forward, although you do need to make some decisions along the way. Basically, all you need to do if figure out how much of the radioactivity in question would be consumed during a single year, multiply that value by an Ingestion Dose Conversion Factor, and there you have it!

For example, if you assume a hypothetical human consumes one liter of the well water you tested each day for a year, after that year was over he/she would ingest 8,180 pCi/liter x 1 liter/day x 365 days/year = 2,985,700 picocuries per year. If you happen to know what radionuclides contributed to the 8,180 picocuries per liter of gross beta activity (it appears some of it is uranium, but I’m willing to bet there are other contributors too!), all you need to do is multiply the intake amount an Ingestion Dose Conversion Factor in order to determine the radiation dose to that hypothetical human. One such collection of factors can be found at the Plexus-NSD web site. (Take care to see that all of your units match up!) Once you end up with a result, then you can start comparing that dose potential to other common radiation doses. Once again, the Plexus-NSD web page just happens to have just such a collection. If you scroll down towards the bottom of the page, you’ll see a listing of dose potentials for typical radiographic procedures, including chest x-rays.

Hopefully this will get you started. However, just a caution that radiation dose assessments, no matter how simple they appear, can always be challenged. Please work through your assumptions carefully and be sure their technical basis is supportable. Good luck!

Q# 13: I am trying to submit these questions again. I have tried twice previously in the last several months without a response. I am unsure if you are receiving my emails. I understand there is a small amount of Americium located inside ionization smoke detectors. Recently, while changing the battery, my smoke detector was placed on my purse and toothbrush and some other personal toiletries in the bathroom. I was concerned about radiation getting on these items. However, I used my toothbrush anyway and figured I would be safe. Could you clarify this? Could the radiation ‘contaminate’ other things by sitting the smoke alarm on or near them? Also, recently I took a battery out of an ionization smoke detector that had been in there for a long time and used it in another electronic item. Could the battery absorb any radiation? Is it safe to reuse the battery in another item without fear of radiation? Should you wash your hands after handling a smoke detector or battery used in one? Thank you so much for your assistance. I have been concerned about these questions. I appreciate your time and expertise. (1/3/13)

Date: January 3, 2013

Answer: Yes, there is indeed radioactivity in almost all smoke detectors. Americium is the element that is used in smoke detectors purchased or installed in buildings and homes to signal the presence of smoke or fire. These are just one of many products identified as a “consumer product” by regulatory authorities such as the U. S. Nuclear Regulatory Commission (USNRC). This designation means that even though radioactivity is found in the product, the radiation levels are considered trivial relative to the benefit obtained from using the device. Therefore, they can be sold on the open market.

Before we go further, we encourage you to visit the “Radioactivity Basics” section of the Plexus-NSD website, click on “Useful Radiation Sources”, then select the category “Consumer Products”. We know you will enjoy reading about many different types of consumer products that contain or involve radioactivity, including smoke detectors.

Now, before I answer your specific question, let me give you a little background information about smoke detectors, which is information which is often sought by others who email us radiation-related questions. Americium-241 (Am-241) is the specific isotope of americium that is used in smoke detectors. Am-241 emits two different types of ionizing radiation: alpha particles and gamma radiation. (Once again, visit our “Radioactivity Basics” section to learn more about ionizing radiation and its different forms.) The alpha particles ionize the air, producing an electrical current. If smoke particles enter the detector, they disrupt this current and trigger an alarm. The alpha particles do not travel outside of the smoke detector which allows the safe of these detectors by the public for their intended purpose.

The construction of these devices is such that the radiation source, containing a small (i.e., on the order of one microcurie) amount of americium, is sealed in a metallic gold covered disk. The threat of leakage is a negligible concern, even for the smoke detectors you have had in your homes for several years. In fact, we at Plexus-NSD have never heard of such an event ever occurring. In addition, simply dropping one of these devices – which are typically sold with a solid plastic casing around the battery, source, etc. – would not be sufficient to dislodge the radioactive material. An individual would have to purposefully break open the device (and the sealed source) to create a problem. This latter situation has occurred on very rare occasions and necessitated the intervention of regulatory authorities to survey the house and undertake cleanup activities as needed.

Now on to answering your questions. You can rest assured that placing your intact smoke detector on your purse, toothbrush, and any other personal item does not present a hazard to you and does not transfer radioactive material to the items. The radioactivity in the smoke detector is firmly confined within that metallic disk. Also, please be aware that the radiation emitted by the Am-241 source does not travel outside the housing of the smoke detector.

It is also perfectly safe to reuse batteries removed from a smoke detector for another item provided the rest of the smoke detector has not been damaged. Batteries removed from a intact smoke detector are not radioactive and can be safely handled by the consumer. If fact, we encourage consumers to make sure that their detectors have properly charged batteries in them at all times so the detectors are always functioning and in a “ready state” to detect smoke and then alarm when smoke is detected. Most detectors emit an intermittent chirping sound when the charge on the battery becomes low, signaling that it’s time to replace the battery.

In summary, smoke detectors are superbly sealed and safe, and they are a great example of the beneficial uses of ionizing radiation. The demonstrated effectiveness of these devices in reducing the death rates from residential fires, especially over the past three decades, is phenomenal. That fact alone far outweighs the trivial amount of radiation exposure (well below the annual natural background levels) generated by their presence in the house.

For further information on this topic, you might want to research additional information on the web, visit a local technical library, and/or contact a local radiological society/state radiological agency in your area. If you want some detailed information on consumer products, including a discussion of smoke detectors, contact the USNRC’s Office of Nuclear Regulatory Research in Washington, D.C. and request a free copy of the draft report NUREG-1717, “Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials”. The easiest way to do this is to simply e-mail the agency at DISTRIBUTION@nrc.gov, provide the title and number of the report, your mailing address, and then wait! Among other interesting information presented in this approximately two-inch-thick document (that’s right, two inches!) is a two-page write-up on . . . you guessed it . . . smoke detectors!

To learn more about human tolerance for radiation exposure, we again invite you to visit the “Radioactivity Basics” section of the Plexus-NSD web page. There you will learn that each and every one of us, by virtue of being alive, are constantly and continuously exposed to radiation. Some of us receive relatively low annual exposure rates, and some of us receive quite high ones, depending upon where we live, what our homes are constructed of, what we eat, what we drink, our lifestyles, and a host of other factors. In all cases, no radiation-related health effects have ever been demonstrated, and in all cases, the radiation doses are much, much higher than those associated with conventional use of smoke detectors.

On a final note, let us say it once more: A functional smoke detector saves lives. Your safety and the safety of any other residents in your house depend on them, so please do not consider removing them.

Q# 14: Hello, I came across your website (great info, look forward to reading it all), and I wonder if you could answer a question first. We use thoriated tungsten electrodes in our fab shop, and are of the practice of grinding/dressing the tips by hand on a belt sander. Recent corporate push for safety in all areas lead me to research the hazards of radioactive particles in the grinding dust. I seem to be getting a lot of conflicting information – for example a Swiss study points out that when used improperly (inadequate dust control, poor hygiene – typical of a weld shop) the dose can be 20 times higher than the legal limit for non-professionals exposed to radiation. (ECNDT 2006 – TH.3.5.5 Kunz Piller). Now I realize that US or Canadian law might not be as strict, but I am not concerned about the legal aspects – if any country on earth has findings that worry me, I will apply those to our workplace as well. So my questions – what is the realistic hazard of using thoriated tungsten for TIG welding? If we follow good hygiene practices and contain our dust, regularly vacuum, and dispose of the dust in sealed bags, we are OK. But what if we don’t? What about the residual dust in the vacuum system, on the walls, in dark corners that never really get cleaned? If we switch to lanthanated tungsten, do we need to consider a major clean-up (wash down, repaint, whatever). I do not want to make a ‘big deal’ of this, but at the same time I am concerned by all the conflicting information. So far, a lot of the material I read suggests that the exposure is very minimal, but this seems to be the exposure to the electrode itself (where the thorium is neatly bound in it’s oxide) and not the dust from grinding that electrode. Finally, when a comparison is made about the exposure/dose compared to other common exposures (normal background radiation, air travel, medical or dental procedures) sure the realistic exposure is low, but somewhere along the line the studies seem to forget that while the does might be very low, it should be considered in addition to all the other exposures. In other words, our welders don’t just weld, they also travel by air, see the doctor, take barium swallows (yuch, just had one of those recently!) so the dose by weld dust is an accumulation of all those other doses. (when I was employed in a nuclear reactor, we had dosimetry badges. If we had any medial procedures done, that was added to our yearly allotment and could affect where in the plant we were legally allowed to work) How dangerous is it really?? Sorry for the wordy question, but I am trying to prepare a reasonable case against thoriated tungsten for next weeks safety meeting. (3/14/13)

Date: March 14, 2013

Answer: As you probably already know, thoriated tungsten electrodes, often called “welding rods”, are widely used in commercial industries, such as aircraft, petrochemical, construction, and food processing, in a process known as tungsten inert gas, or “TIG” welding. In TIG welding, an electrical arc is produced between a nonconsumable tungsten electrode and the work metal. This heats up the metal.

Part of what makes these welding rods so good at what they do is the fact that they contain a small amount of thorium, a naturally-occurring radioactive material. Adding a bit of thorium to the tungsten before the rods are made results in easier arc starting, greater arc stability, reduced weld metal contamination, higher current-carrying capacity, and a longer electrode lifetime.

Before the manufacturers of welding rods were authorized to distribute them in the United States for general use, they were required to prove to the U. S. Nuclear Regulatory Commission that they were safe under any potential use situation. This includes during welding and during grinding of the electrodes. A number of studies have been done to prove just that, and the result is that thoriated tungsten welding rods may indeed be used without regard for potential radiological ramifications. (You can read more about the use of the safe use of these welding tools by visiting the “Radioactivity Basics” section of the Plexus-NSD web page. Go to Chapter 9: Useful Radiation Sources, and then click on the welding rod write-up.)

On the other hand, there are also non-radiological issues that must be addressed in any work place. Whether using thoriated tungsten, a radiologically-inert welding rod, or performing any other industrial operation, there are requirements for ensuring adequate ventilation and control of dust. If you have concerns along these lines, please do not hesitate to contact the safety representative at your facility. This professional can give you information about the air quality in your work place and put those measurement results into perspective with respect to applicable regulations and requirements. If poor air quality is found to be present, he/she is in the best position to improve the ventilation and air flow in the area and to re-test it after changes are made to ensure optimum conditions are met.

However, let me reassure you that the radiological aspects of using thoriated tungsten welding rods are not significant considerations. The dose potential via all pathways is indeed low, otherwise they would not be exempt from licensing here in the United States. You might want to check with either Health Canada or the Canadian Nuclear Safety Commission to see if they maintain a similar position in your country.

You do raise an important point when it comes to summing the radiation dose from all sources one might encounter on a daily basis. As it turns out, there are quite a number of agencies that have compiled that very information, with some of those write-ups being quite recent (see National Council on Radiation Protection and Measurements, Report No. 160, “Ionizing Radiation Exposure of the Population of the United States”, 2009). In today’s world, the greatest contributor to our normal background radiation dose that comes from just being alive is generally from medical diagnosis/treatment. Second on the list is exposure to radon and progeny in our homes. Wa-a-ay down on the list is industrial exposures . . which comprise less than 0.1% of the annual average dose of 620 millirem (6.2 milliSievert) just from being alive. (To put these doses into perspective, please go to the “Radioactivity Basics” section of the Plexus-NSD web page and select Chapter 4 on “Radiation Risks”.) The normal safety precautions you take at your place of business will ensure the dose potential from TIG welding remains a small fraction of your co-workers’ of that incurred off the job.

Q# 15: As a high energy 250 MeV medical proton accelerator manufacturer, we are often faced with shipping materials that are slightly radioactive (< 0.5 mr/hr on surface). The problem is the objects are accelerator parts that were activated incidental to beam production. The exact isotopes and their quantity are unknown. Is there a shortcut to applying the DOT limit tests, or a general way to classify these as not radioactive from DOT perspective. Thank you for your answer and for a great informational website. (4/8/13)

Date: April 8, 2013

Answer: All of us CHPs line up for opportunities to respond to questions we receive via the Plexus-NSD web site . . . unless they involve shipping radioactive materials. It takes special skills to interpret and understand those pesky transportation regulations and I must admit, most of us don’t keep up on them as well as we should. Therefore, I forwarded your question to a member of our nuclear services staff who has her finger on the pulse of the Department of Transportation (DOT) and their requirements for “rad shipments”.

As it turns out, the answer our shipping guru gave me is pretty straight forward. By their very definition of “Radioactive Material” in 49 CFR §173.403 (Definitions), the DOT makes it clear that knowledge of the radionuclide content of a shipment of radioactive material is a basic requirement. Here is what the citation says: “Radioactive material means any material containing radionuclides where both the activity concentration and the total activity in the consignment exceed the values specified in the table in §173.436 or values derived according to the instructions in §173.433.” In other words, one can’t even determine whether a shipment is exempt from DOT rules unless the activity (and activity concentration) is known. And one can’t determine the activity (or the activity concentration) without knowing what radionuclides are in the mix.

There are provisions for grouping individual radionuclides in §173.433(e) and §173.433(f) when the activities of some are not known. However, you would still need to know their identities. Your best bet is to look at the materials being irradiated during accelerator use (e.g., steel, concrete), determine the highest probability isotopic mixture being produced (e.g., Co-57, Co-58, Fe-59, Eu-152, Eu-154), do whatever dose modeling is necessary in order to back-calculate concentrations inside of shipping containers (i.e., MicroShield) from exposure rate measurements, and enter those results as your best estimates on shipping manifests. Good luck!

Q# 16: Hi, I’m, my grandmother was vacuuming her bedroom a couple years back, when she caught the electric cord on her radium clock. it came off the table and hit the floor.the clock cracked open the plastic lens hands dial came off.she said she took it in the bath room and tried to fix it put it back together,after seeing it could not be fixed, she saved some of the part,s hands, and cut off the cord. for someone she said might need it, (she went through the great depression, she saved everything.) after she passed away. myself my wife and son have been living in the house, about a year ago when cleaning out the bathroom drawers we found some of the old clock parts power cord clock hands, i don’t think the plastic lens or dial was in there, this clock had a white case with a black dial. sorry for being so long, but here is my question,the bathroom counter top is tiled in to the wall with a mirror in front of it.we have been using the drawers and have been putting tooth brushes combs makeup in them, and getting ready everyday at that area.i know from reading your site everything is somewhat radioactive,and i have known about old watch and clocks and radium on them. that is why I’m worried about radium dust flakes that could be in the drawers or still on the tiled counter top. contamination my grandmother could have caused without knowing..she also hand some old watches, in a wood jewelry box in some basement cabinets. but only one was missing its crystal and all where in the box. my cousin wanted them and didn’t seem to care, so do i need to be worried about contamination? is it safe to put thing,s in that area , did basic house cleaning take care of any problem? thank you for your time. (5/3/13)

Date: May 3, 2013

Answer: Before we get to your specific question, we would like to ask you one: Are you sure your Grandmother’s clock contained a radium-bearing dial? These items were immensely popular around World War II, but they weren’t cheap and other materials quickly replaced the use of radium in these devices. Not all manufacturers of radium watches and clocks marked their devices showing that radium was indeed incorporated into the phosphor used to ‘light up’ the time. What’s more, some manufacturer’s sold products as “radium clocks” when in fact there was no radium involved in their construction at all.

Let’s assume for now that the parts you uncovered, specifically the hands, were painted with a radium phosphor. However, in most cases, the phosphor used in the paint of those old devices has long since expired, so the dials and hands won’t glow in the dark any more. If the watch hands you recovered do still glow in the dark, they are probably a lot newer than you think, and we again can’t be sure what radioactive material, if any, was used to give the dial its self-powered feature. The bottom line is that trying to estimate the radiation exposure potential of these items would be nothing more than speculation.

Here is what we can tell you. If an individual wore a radium-bearing wrist watch – and there are quite a number of those still around and functioning, believe it or not! – he or she will receive a gonadal dose-equivalent of about three (3) millirem per year (see the “Radioactivity Basics” section of the Plexus-NSD web page for more information on these units). For watches that are simply being stored and not worn, as would be the case for a clock, the radiation doses, if any, would be negligible. For a couple of watch hands and not the entire clock face, “negligible” would likely be an over-estimate.

However, your concern is whether the broken parts you discovered are scattering the radioactivity around rather than keeping it confined within its paint matrix. The nice thing about radium is that it emits radiations during its decay that are quite easy to detect. If your watch hands have been leaking, you can find out about it easy enough by just making some radiation measurements near whatever has come in contact with it. If you don’t have access to a hand-held radiation detection instrument, you might want to place a call to a nearby hospital, nuclear medicine facility or a local university to see if they can give you a hand. Alternatively, you can always ask the bureau of radiological health in your state for assistance; these professionals are in the business of controlling radiation doses associated with gadgets such as yours, so they are well-equipped to evaluate the ramifications and take whatever protective action they deem necessary.

Bear in mind that if the clock hands have been leaking, normal housekeeping activities, like dusting and washing down surfaces, would remove whatever was deposited. Think of it as spilling some salt on a counter top. One swipe of a sponge would quickly move most of it into a nearby sink. More swipes as the counter is cleaned on a daily basis would end up removing it all, eventually.

Finally, let’s put some of this information into perspective. We know more about the potentially-harmful effects of radiation exposure than we do for just about any other carcinogen. However, radiological risks are only demonstrable when whole body doses exceed 10,000 millirem. And even then, effects from doses up to 50,000 or 100,000 millirem are temporary and reversible. As you can see, the dose potential from possessing a few parts from a broken radium clock – assuming there is radium in the clock, mind you! – is well below these values.

Q# 17: I am doing a research essay on shielding of a 14 MeV neutron generator and wish to estimate the required thickness of some shielding materials () for a certain attenuation. How do I find the neutron removal cross sections of those materials at different energies between 100 KeV to 10 MeV? Thank you. (5/11/13)

Date: May 12, 2013

Answer: You’re in luck! Our good friends at Brookhaven National Laboratory (BNL) in Upton, New York have been compiling cross section data for many, many years. Here is a link to an old paper that was prepared for submission to the “Handbook of Chemistry and Physics” that contains a whole bunch of thermal neutron cross sections: http://www.osti.gov/bridge/servlets/purl/26983-3lpvXQ/webviewable/26983.pdf. If that doesn’t do it, you might want to check out the impressive set of resources available from BNL’s National Nuclear Data Center: http://www.nndc.bnl.gov/. In addition, the Nuclear Data Section of the International Atomic Energy Agency has prepared an Atlas of Neutron Capture Cross Sections at this web site: http://www-nds.iaea.org/ngatlas2/. Finally, don’t forget to check out the excellent guidance and reference information published by the National Council on Radiation Protection and Measurements (http://www.ncrppublications.org/). Hopefully you can find what you’re searching for somewhere within these excellent sites. Good luck in your research!

Q# 18: I was talking to my friend, and somehow we stumbled upon the question of radioactivity. I stated, ‘Well, everything is a LITTLE radioactive’, to which he replied, ‘Okay, that’s just not true.’ After thinking about it, I realized that if everything were radioactive, why does it not say so on the periodic table of elements? The answer to this question on this website seemed rather vague, stating that everything certainly RECEIVES radioactivity. But what’s the straightforward answer? Is every element, no matter how negligible, radioactive? If I left a plate on a table in a sealed off, airtight room, would it eventually disintegrate in billions or trillions of years? Thanks. (5/17/13)

Date: May 17, 2013

Answer: Talk about a swell topic of conversation for a cocktail party! All of us CHPs at Plexus-NSD sure would like to hang out with you and your friend as you sure have some interesting discussions!

But enough of that. Let’s start first with some basic information before we get to your specific question, which is a good one by the way! The definition of “radioactivity” is the spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction. (To learn more about this interesting phenomenon, go to the “Radioactivity Basics” section of the Plexus-NSD web page.) The operative words here are “unstable atomic nuclei”. Generally speaking if an atom has too much mass in its nucleus, such as more neutrons than protons, the nucleus becomes unstable and nature doesn’t like instability. Therefore, the nucleus tries to get rid of that excess mass by emitting “radiation”, in the form of particles or photons.

Let’s take a look at an element that is definitely a part of life . . . uranium. Uranium is terrestrial in nature in that it was around when the earth was formed, and you can easily find it in your back yard (i.e., in the dirt and rocks). All isotopes of uranium are radioactive, meaning they are trying their best to drop some weight. But what’s interesting is that the uranium isotopes “decay” into other radioactive isotopes . . . which decay into others, which subsequently decay into others. Eventually, this chain (or series) of radioactive elements finally reaches what is typically referred to as stable lead (i.e., the element Pb). At that point, the series stops.

When the earth was formed, there was more uranium around than there was stable lead. However, time marches on and the amount of stable lead is increasing. In fact, we use the relationship between uranium and stable lead to give us clues as to when the earth was formed. What’s important here is that stable isotopes are typically the most abundant isotopes simply because they don’t decay any more.

Without getting too deep into the realm of nuclear physics, atoms need to have enough energy to overcome an energy barrier before they can decay to form more stable atoms. With that said, there is some scientific basis for the position that some atoms still have too much mass in their nucleus, but can only occasionally leap that energy barrier, leading to the conclusions that there really is no such thing as a “stable” atom. Instead there are just atoms that are decaying so darn slowly that their “half life” is too long for us to measure. An interesting position, no?

So there you have it. We have radioactive atoms, and we have stable atoms. However, its possible those stable atoms may also be radioactive but we just can’t confirm it. So in the real world, you and your friend are both correct in your positions. With that, here’s another topic for you to cover the next time you get together . . . does everything “contain” radioactivity? In other words, can we find radioactive atoms in the air we breathe, the water we drink, the food we eat, the ground we walk on, in our homes, in our cars, in our place of work, and even in our own bodies? If you or your friend know the answer to this question, you are in the minority as most people don’t!

Q# 19: I would like to know how to calculate the conversion factor of I-123. Using a dose calibrator from Atom Lab (6/6/13)

Date: June 6, 2013

Answer: Dose calibrators are interesting pieces of electronics. Most of them contain an ionization chamber, and they are used to assess the amount of radioactivity in a radiopharmaceutical before it is injected into a patient. As one might imagine, a functioning dose calibrator is a necessary part of a nuclear medicine operation.

We’re not sure what you mean when you ask about a conversion factor for I-123. However, the reliability of a given dose calibrator’s response is assured by proper calibration and by performing and documenting four specific quality control tests: (1) Accuracy; (2) Constancy; (3) Linearity; and (4) Geometry. Let’s cover each of these briefly.

Each calibrator’s response needs to be traceable to nationally-recognized standards (i.e., the National Institute of Standards and Technology). This should be done at least once per year or as otherwise recommended by the manufacturer of the calibrator. Typically calibrators are sent to an off-site facility who is appropriately licensed to provide the necessary calibrations.

For the four quality control test, let’s start first with the one for accuracy, which is how you show the calibrator is giving you the correct “reading” over the photon energy scale of interest. Usually low, medium, and high energy standards (i.e., Cobalt-57, Cesium-137 and Cobalt-60) are placed into the calibrator and the readings recorded. The amount of radioactivity on each standard needs to be decay-corrected, as necessary, then the measured results compared to the actual results. If the measured value is within 10% of the actual value, the calibrator is considered to be sufficiently accurate.

The test for constancy is used to show the calibrator’s response is reproducible day after day. For this test, one of the aforementioned standards is placed into the calibrator and the activity recorded every day the device is in use. As with the accuracy test, this value needs to be within 10% of the actual value. Plotting the measured values can be particularly helpful here as a graph can quickly show if the response is starting to trend high or low.

The linearity test is used to show the calibrator’s response is linear over varying source activities. In general, linearity from microcurie to the millicurie source activities is the range of interest. Most facilities use an isotope with a relatively short half-life like Technetium-99 metastable (Tc-99m) for this test. The standard is placed into the calibrator, a reading obtained, and then subsequent readings are made at pre-determined time intervals until the initial activity drops by an order of magnitude or so. Once again, measured and actual results are compared.

The test for geometry is used to show the calibrator’s response is reliable regardless of the sample size or geometry. This test is typically performed for the types of vials and syringes typically used for patient radiopharmaceuticals. To test a 10 milliliter syringe, for example, a milliliter of a specific standard is placed into the syringe and the measurement recorded. The activity is then diluted with water to two, three, four and higher milliliters and readings recorded after each measurement. If the measured-vs-actual response is geometry dependent, that’s not a good thing.

Going back to your question, if you are using Co-57, Cs-137 and Co-60 for your accuracy determinations, the energy range you are testing runs from 136 to 1,333 thousand electron volts (keV). The isotope I-123 emits a 159 keV photon during 83% of its decays, which is within that energy range. If your calibrator is also confirmed to be constant, linear and geometrically independent, and if it demonstrates accuracy of less than +/- 10% over the 136 to 1,333 keV energy range, the reading it gives you when you place a vial or syringe of I-123 into it should be reliable.

Q# 20: What levels in pico curies per gram are a problem for spent refractory? I have data but I cant find any EPA guidance and my local class II landfill is clueless…They have a detector at the gate but cannot tell me how much will set it off–Thanks! (8/30/13)

Date: August 30, 2013

Answer: Your question is a good one, and you’re not the first to ask it. However, the answer to your question is “it depends”. What does it depend on? A lot of things, including the type of refractory, where it was manufactured, what kinds of gate monitors the landfill has, how those monitors are calibrated, what the background is in the location of the gate monitor, and lots more.

As you already know, some types of refractory material contain zirconium oxide, a compound that gives the refractory its fire-resistant qualities. Zirconium is an ore and, depending on where it was mined, it can contain anywhere from trace to “definitely measurable” uranium and thorium. Then we have the refractory production process, which in some cases can concentrate the uranium and thorium even further.

Companies that purchase and use refractory eventually need to dispose of it, which is where the fun begins. Depending upon the amount of uranium and thorium in the refractory, and the mass of refractory being disposed of, it is certainly possible for the radiations being emitted from the refractory to trigger the alarm of a landfill portal monitor. Of course the likelihood of an alarm depends on the type of portal monitor in use, where the alarm level is set, and how the portal monitor accounts for the presence of background radiation. (If you check out the “Radioactivity Basics” section of the Plexus-NSD web page, you can see that radiation is everywhere!)

Some State regulatory agencies have set some radiation-related criteria whereby materials or items can be rejected from a landfill. It is in these states where we see lots of portal monitors in use. In States where there are no specific criteria, portal monitors are few and far between.

In the States interested in natural radioactivity levels going into landfills, some have adopted criteria that are based on the concentration of radioactivity in a particular load. Others have set criteria that are based on “radiation exposure rates above background”. So here we are again with respect to the disposition of spent refractory; the level that might trigger a concern at your local landfill depends on where your landfill is located and what your state regulatory agency requires.

What is unfortunate is that landfill portal monitors, most of which can do a great job of detecting radioactivity no matter where it comes from, are often “black boxes” to landfill operators. They purchase and install one, but have no idea how it works, how it should be set, what an alarm means, and what to do if an alarm is encountered. It sounds like your local landfill falls into the black box category.

However, you did mention that you have some data from your spent refractory. We’re not sure if you mean analytical data from a laboratory or exposure rate data measured using hand-held instruments. In either case, we suggest you provide those data to your landfill operator and let them tell you whether your refractory meets their acceptance criteria or not. If they don’t know, then they really need to contact their state regulatory agency to find out. If they’re not willing to do this, it may be time to find another landfill. If it turns out your spent refractory contains too much natural radioactivity to render it eligible for conventional landfill disposal, give us a call and we’ll see if we can’t provide you with some options.

Q# 21: Hello, and first let me say your website is among the best, most informative sites I’ve ever seen. The information is tremendous. With that said I hope you can help ease my mind due to the number of x-rays my 12 year old son just had last week. My son was playing baseball (he loves to play!) and was playing center field. A ball was hit, just out of his reach so he dove to try and catch it. Unfortunately, in the process of diving for the ball his body was horizontal in the air and when he came down he landed hard on his hip and injured it. For several days he complained about hip, knee, and thigh pain. So we took him to his doctor who ordered eight x rays of his hip, upper leg, knee, pelvis area, etc. It looks like it’s nothing now other than a hip contusion but he is being sent for an MRI this week since he’s still in bad pain. I am NOT concerned about the MRI, because I understand from your site and other answers you’ve provided MRI’s do not contain radiation, but I am VERY concerned that having EIGHT x-rays in the same location at the same time could be very dangerous or cause cancer for him later in life. Can you let me know if 8 x rays is too many? Thank you so much. (3/18/11)

Date: March 18, 2011

Answer: Let us start off first by saying thank you for your kudos on the Plexus-NSD web site. We love feedback of any kind, and we particularly like it if it is good!

Now let’s move on to your question, starting first with a little review. If you’ve browsed your way through the Plexus-NSD web site, you’ve probably learned that an individual can be exposed to radiation in a variety of ways. These include doses from natural background sources, which in the United States averages about 610 millirem per year for the whole body, but ranges from 400 to over 1,500. (In other parts of the world, it can be significantly higher with no corresponding detrimental health effects). In addition, certain individuals are exposed occupationally to radiation as a result of their livelihood. These individuals, which includes most Plexus-NSD employees, are typically authorized to receive higher than natural background doses. Still others receive radiation exposure from medical diagnosis and treatment applications. This latter situation sounds like the one that is of particular interest to you in light of your son’s recent injury.

X-rays constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics”section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

Diagnostic x-rays are still probably the most commonly employed form of radiology, a science that generally speaking, uses imaging techniques to allow doctors to see inside a patient’s body. Examples in addition to x-rays include angiography, breast imaging (mammogram), computerized tomography (CT) or “CAT Scans”, magnetic resonance imaging (MRI), nuclear medicine procedures, and ultrasound. However, your interest is x-rays, so let’s just cut to the chase.

The typical radiation dose to the limb from a conventional diagnostic x-ray is on the order of six (6) millirem. (To learn more about radiation-related units, please visit the “Radioactivity Basics” section of the Plexus-NSD web page at http://www.iem-inc.com/primer.html.) The dose associated with an x-ray of the pelvis is about 70 millirem. In your son’s case, we believe you said he had a pelvic/hip x-ray and seven x-rays of other portions of his limbs, which is a total of 7 x 6 + 70 = 112 millirem. Even though it was only a portion of his body subject to the diagnostic procedures, let’s assume for the sake of discussion that he received a whole body dose of 112 millirem. That value is well-within the range of the background radiation dose across the US by virtue of being alive, and is far too low to result in any radiation-related health effect. For more on that, take a look at the write-ups on radiation risk in the Plexus-NSD web page at http://www.iem-inc.com/prisk.html.

We would be remiss if we didn’t remind you that the number of x-rays your son had in order to diagnose his injury was determined by his physicians. As you know, doctors take ethical vows to administer only those procedures that are deemed necessary to diagnose the patient’s medical situation, and in this day and age there is a heightened sensitivity to radiation exposure of children (see the “Image Gently” web site hosted by the Society of Pediatric Radiology at http://www.pedrad.org/associations/5364/ig/). The benefits obtained by ordering those procedures by far outweigh the radiological risks associated with them, and we can say with confidence that your son’s risk of radiation-related injury (i.e., cancer) as a result of his recent series of diagnostic procedures cannot be distinguished from the natural incidence of cancer in the human population. On the other hand, think of the pain, suffering and possible long-term ramifications he could suffer if his doctor did not have access to such an important diagnostic tool as an x-ray machine.

As a patient, however, we definitely recommend you exert your rights and those of your son whenever possible. You should always ask questions of your health care professionals to alleviate any concerns you might have prior to receiving radiation exposures or any other invasive procedures. They are prepared to respond to these issues and to put everything into perspective in light of your medical condition. You may find that a dialogue of this nature will be helpful in easing your anxieties if this situation should arise again in the future. In the meantime, we hope your son’s condition is improving and that he will soon be back on the ball field!

Q# 22: Thank you in advance for this great service. I read many of the questions on your site but I did not see one close to mine and I doubt there would be one like mine. I ordered an intra oral camera from a company in Tokyo. The camera will be used daily on patients in their mouths except when in the pocket of my dental lab coat all day, every day. Should I have any concern over possible radiation contamination of the product? Should I cancel the order or take it to a testing laboratory to check to see if it has radioactivity? I do have some connections as my original field of study was physics and I live close to Argonne National Laboratory. I have friends who work there and probably would be able to link me up with someone with a scintillation counter. The camera was on back order and has not shipped yet, so I don’t think it has been manufactured yet. I have a choice of many other products from other manufacturers. Do you have any advice? Thank you. (3/22/11)

Date: March 22, 2011

Answer: The events that transpired recently in Japan as a result of the earthquake and tidal wave were definitely tragic, and Plexus-NSD’s collective hearts go out to the local population for their loss and their struggle as they rebuild. The Fukashima Daiichi nuclear power station also took a big hit when they were unable to power or use their recirculating pumps. In order to bring those plants under control, containment buildings were intentionally vented as a means of releasing pressure. In addition, some auxiliary buildings were damaged during follow-on events that further contributed to the release of radioactivity. However, when all is said and done, history will show that the health impacts from the damaged nuclear station will be dwarfed by the devastation imparted by the earthquake.

We at Plexus-NSD have received quite a number of calls about the import of products, equipment, containers, foodstuffs and other merchandise from Japan and we understand our callers’ concerns. Depending on specific circumstances, a monitoring program may be required in order to safely receive and use Japanese exports. However, such a program is not necessary for your pending purchase.

First of all, containers used to transport cargo across the seas land first at a port of call, where they are subject to radiological screening to be sure they don’t contain anything that might present a risk. (The events of 9-11 sure have changed the way we do international business!). So if a container from Japan happened to have been sitting outside and in close proximity to the Fukashima station during all of the recent events, and if contamination of significance from the plant ventings was deposited on those containers, port screening would likely catch it, at which time decisions would be made about decontamination or returning the container to the shipper.

If only clean outer containers are used for shipments, it is certainly possible inner packaging could have some residual radioactivity on it if the site where it originated was close enough to the Fukashima station and if the packaging was somehow sitting out in an area where deposition could occur. However, it is our understanding that Japan is attempting to exercise some control over their exports so they can also control the release of residual contamination. Under normal circumstances, this country is certainly capable of instituting an effective contamination control program, so we suspect they will be successful now. We also suspect a formal certification program will be put in place by most exporters very soon so they can get their products back into the international marketplace.

An important point to make here, and one that is pertinent to your question, is that the radioactivity released from the Fukashima station does not make other things radioactive. Yes, contamination, just like dust, may be deposited on a package or item that was in close proximity to the plants, but once that contamination is removed the package or item would have benign radiological characteristics.

Your question pertains to a camera with parts that will be inserted in a patient’s mouth. On the remote chance some residual radioactivity from the damaged nuclear plants ended upon on some of those parts, your routine sterilization procedures would be more than effective at removing it. Radiological contamination control is similar to pathogen contamination control – what works for one will generally work for the other.

The bottom line is that, by the time you receive the camera you ordered from Japan, the manufacturer will be able to certify it “clean” before it leaves. Once it reaches you, your routine sterilization program will ensure the pathogen and radiological safety of your patients. We don’t believe there is sufficient radiological justification to cancel your order and purchase your camera from another manufacturer, but you can certainly do that if it would make you and/or your patients more comfortable. You can also have your camera “screened” for the presence of residual radioactivity if you need documentation that it is unimpacted. Just give your State radiological control board a call and ask them to refer you to one of their registered service providers.

Q# 23: I do not work in the nuclear industry, but was required to review about 15 dusty boxes of documents (containing rad surveys, dosimeter badges, and other HP documents) from the 1960s that came from a former nuclear research facility near Karthus, Pennsylvania, often referred to as the Quehanna nuclear facility. The facility had a small reactor that was used for research, but the primary use of the facility was for the processing of Strontium-90 fuel in hot cells for the development of Space Nuclear Auxiliary Generators. The Strontium 90 project was terminated by 1970, but many years later it was determined that significant quantities of Strontium-90 had been leaching out of the hot cells, and that the hot cells and many parts of the facility were significantly contaminated with Strontium 90. I am concerned about having reviewed these dusty boxes on the basis that they could have been contaminated with Strontium 90. Are my worries reasonable? In other words, is there a likelihood that those boxes might be contaminated with Strontium-90 to the extent that it might impact human health? (4/18/11)

Date: April 19, 2011

Answer: First off, thanks for your kind comment on the “Ask A CHP” section of the Plexus-NSD web page. We love to receive feedback and particularly like it if it is good feedback! Now on to your question . . .

In order to evaluate one’s radiation dose potential, we would need to know something about the amount/type of radioactivity present and the individual’s time and motion with respect to that radioactivity. Since we don’t know any of those things, I’m afraid any answer I might give you about your radiation dose potential during your review of the 15 boxes of records would be sheer speculation.

I can, however, give you some ancillary information that might be of use to you. Once key point is that the former research facility had to have a license in order to operate. That license required them to control all radioactivity at their site such that it would not be released to members of the public. If the organization complied with all of their license provisions, one might reliably conclude that they did not release boxes of records that were “surface contaminated”.

A second key point is that the paperwork you described sounds like general documentation all licensees are required to retain. These documents are almost never stored in radiologically restricted areas, but instead kept in offices and administration buildings. Therefore, this might also lead us to conclude that the boxes and their contents were clean.

A third key point is that your employer has a legal obligation to inform its employees of workplace risks. Therefore, you are well within your rights to raise your concerns to your supervisor. If he or she does not know the answer, they can certainly find out by simply having someone come in an check out the radiological status of those boxes. However, if your supervision does not pursue an answer to your questions, you area also within your rights to contact your State bureau of radiological health to ask them the same questions. The State representative will first ask you if you discussed the matter with your supervision, so please be sure to do that first. They will then take action necessary to provide you with a response.

The bottom line is that the boxes you handled probably were not radiologically contaminated, but we can’t say that with confidence. Therefore, you’ll need to take this to the next step and query your employer. Hopefully you’ll have the answers you seek soon.

Q# 24: I see different half-life time frame given on the web – some say it’s 8.04 days and some say it’s 8.02 and others just say it’s ‘about’ 8 days. What is the accurate half-life of I-131? (4/19/11)

Date: April 19, 2011

Answer: Before we get to the meat of your question, let me relay some information about the concept of “half life” and how it is determined. So please bear with me as we set the stage.

Radioactive (unstable) substances emit different types of ionizing radiations through a process known as “radioactive decay”. They do this in order to reach a stable state. The term half life denotes the amount of time required for one-half or 50% of the radioactivity to decay or transform itself to another isotope or element. Since half-lives are unique to each radionuclide, it serves as a handy “fingerprint” for identification purposes.

The concept of half-life relies on a lot of radioactive atoms being present. As an example, imagine if you could see inside a bag of popcorn as you heat it inside your microwave oven. While you can’t predict when, or even if, a particular kernel will “pop”, you can observe that after about three minutes, all of the kernels that were going to pop had in fact done so. From that observation, you could come up with a “popping” half-life (i.e., the time necessary for one half of a bag of popcorn to pop) of about a minute and a half.

In a similar way, we know that, when dealing with a large collection of radioactive atoms, we can predict when one-half of them will decay, even if we do not know the exact time that a particular atom will do so. The bottom line is that, on an individual atom basis, the half-life is not a constant value. On a collective basis, however, it remains pretty steady.

Something else interesting is that there are a number of ways to measure half life. Let’s say we provide several students in a high school class with a short-lived radionuclide and ask them to count it several times (for a fixed period of time) over the course of a few minutes using a typical lab instrument such as a Geiger-Mueller (G-M) detector. Each of these students will report somewhat differing results. This is expected since there are always variables involved in experiments like this (e.g., use of individual instruments with inherent variability, human factors, etc.). However, if the class results are averaged, the result is generally a half-life that is amazingly close to published (literature) values.

To measure very, very long half lives, there are a number of other measurement methods available to us. However, each again comes with its own level of statistical precision. One handy method is a direct determination of the decay rate by measuring the decrease in the number of atoms (or the increase in the number of atoms of a daughter radionuclide) relative to another radionuclide of the same element. For this analysis, a mass spectrometer is used. Another method determines the disintegration rate of a sample containing a known mass of the element (radionuclide) in question. This is known as the “specific activity” method. Mass spectrometric analysis of the sample is performed to correct for other radionuclides that may be present.

There is also a calorimetry method, where the rate of heat production from a known mass of a radioactive substance is determined. Yet another interesting approach is to measure the decay rate of a parent substance by periodically removing and radio-assaying (by mass spectrometry) a decay product. One might also determine the specific activity of a sample by chemical and/or isotopic analysis of naturally-occurring radionuclides by making some assumptions about the sample history (i.e., age, chemical or isotopic fraction, etc.). There is also the “yield” method where radioactivity from a sample containing a number of atoms is calculated from the expected yield of the reaction by which it was produced.

Finally, there is a delayed coincidence/nuclear recoil method that is used to assess the half-life of very short-lived ground states and most fission isomers, or estimating the half-life based on decay energy, level structure and certain theoretical considerations. (Usually this method is used for alpha particle emitters for which half-lives can often be predicted from the alpha energy to within an order of magnitude or so.)

In any event, the catalogues of half-lives of the various radionuclides are, indeed, only estimates. And it is certainly possible that there is no such thing as a stable isotope . . . just one with a really, really, REALLY long half-life. Fortunately, research in these areas are still on-going, and new estimates are published every year.

Now let’s finally get to your question – the “accurate” half-life for Iodine-131 or I-131. This radionuclide decays by emitting beta particles and gamma ray photons. The half life of I-131, as determined by various sources via measurement of the time-decay of the radiations emitted, is reported in C. M. Lederer’s “Table of Isotopes” (the CHP’s bible on radioactive elements) as 8.040, 8.085, 8.054, 8.067, 8.073 and 8.070 days. The average of these six determinations is 8.065 days. Therefore, the most accurate value is about eight days.

By the way, if you have not already done so, we invite you to read the “Radioactivity Basics” section of Plexus-NSD web site. Specifically, Chapter 7, “Decay and Half-Life” discusses the half-life concept in a fair amount of detail. You might find some other useful bit of information about this fascinating aspect of radiation and radioactivity.

Q# 25: Should we be concerned about possible radioactity from products coming from Japan or products from other countries that may have parts in them that originated in Japan? What percentage of products coming into the United States are actually scanned for radioactivity? (4/29/11)

Date: April 29, 2011

Answer: What you are referring to is the tragic state of affairs in Japan as a result of the March 11, 2011 earthquake and tsunami. We’ve all been watching the situation unfold at the Fukushima-Daiichi nuclear power station, where TEPKO is struggling to bring damaged reactors back under control. However, the majority of the impact from the intentional and unintentional release of radioactivity from these units has been generally confined to their general neighborhood, although fission products are being measured at various distances from the site.

Here at Plexus-NSD we have received quite a number of calls from companies who import products and materials from Japan who are as concerned as you are about how to keep from also importing some of Fukushima’s radioactivity. While it is highly likely that some goods, depending on location and how they are being handled, may contain residual contamination from the plants, we are concerned about the rush to set up some sort of screening program, regardless of whether it will be effective in detecting residual radioactivity at appropriately low levels.

Firms who import goods and materials from Japan should use reason when developing their approach on what to accept and what to reject. Decisions should take into account when materials were manufactured, where they were manufactured, how they have been stored, and variety of other considerations. One should also consider the fact that contamination co-mingled with bulk material via deposition or mixing with contaminated water is not easily detected with hand-held radiation detectors, meaning a sampling and analysis program would be more appropriate. Of course, that program also needs to have a solid technical basis because analyzing for the wrong thing or with inappropriate detection, error and QC limits can also result in useless and misleading information.

It is possible to institute a sound and reliable program for assessing residual radioactivity in products that originate in Japan. However, it will involve more than buying up all of the available Geiger Counters from a local hobby shop and handing them out to all of your shipping/receiving personnel. Depending on the products being evaluated and how a particular company operates, screening procedures could very well involve a combination of measurements and analyses, but each needs to have the technical basis for each step clearly defined. The programmatic approach also needs to be based on standard industry practice for the protection of members of the public, compatible with the company’s existing material acceptance process, and incorporate realistic and defensible criteria against which measurement/sampling results will be compared.

The goal of any radiation monitoring program is to first do no harm. A poorly-defined or inappropriately implemented program can do just that by generating information that cannot be interpreted or, worse yet, misinterpreted. Decision-making needs to be based on factual, defensible information, whether it involves the acceptance/rejection triage program or a surface contamination screening program. If Plexus-NSD can be of professional service to you in evaluating risk potential, program design or simply providing technical guidance to facility quality control personnel, we would be pleased to do so.

Q# 26: I am a novelist (All the Stars Came Out That Night, Dutton 2005) and am researching radiation. Could you possibly answer a couple of questions? 1. How are radioactive materials protected in universities? something like a safe? Or a locked room? 2. How are they safely disposed of? Who comes around to pick them up and where do they take the used materials? (4/29/11)

Date: April 29, 2011

Answer: We wish you the best of luck on your up-coming novel, and all of us at Plexus-NSD look forward to reading it . . . especially if it has something to do with radiation and radioactivity! Your questions are good ones, but as you probably already suspect, they don’t have simple answers. How a university might store or dispose of licensed radioactivity depends upon the type of license they have, what they are licensed to possess (type, quantity and form of the radioactivity), where they are located, and a number of other issues.

For example, a university that has been issued a research and development license only for the purposes of doing something like Mossbauer experiments, might possess only a few sealed radiation sources with relatively low activities. These would typically be kept in a locked cabinet, safe or even out in an experimental area as long as it has a locking door. Another university that has been issued a broad scope license for radionuclide uptake testing, operation of an irradiator or neutron time-of-flight studies would have a wide variety of storage options and controls in place, including but not limited to background determinations and fingerprinting of authorized users, redundant locking systems, water-filled pools and dense shielding, large containers filled with paraffin (for the neutron sources), locking laboratories, locking fume hood systems, and more.

As far as disposal is concerned, every single licensee in the U. S. is required to dispose of radioactivity that is no longer in use by one of the following methods only: (1) By transfer to an authorized recipient (i.e., another licensee); (2) By decay in storage; (3) By release in effluents within the limits specified in applicable regulations; or (4) As authorized by their regulator. In the case of the aforementioned university that only possesses sealed sources, these could be sent to another licensed university, or disposed of at a commercial waste disposal facility, although the latter option is severely limited to licensees in specific states only. The university with the broad scope license might have routine pickups of their lab waste (e.g., rubber gloves, protective clothing, sampling media, filter paper, pipettes, syringes, etc.) on a monthly or quarterly basis, depending on how much waste they generate and how much their license permits them to store on site. There are licensed waste brokers who work with both licensee types to secure the most appropriate and the cheapest disposal options for them . . . which isn’t easy to do! Radioactive waste disposal, no matter how you look at it, is costly.

These are just a few examples. There are as many more as there are licensees. Every licensed site is different and each has different material storage requirements and disposal needs. In all cases though, the licensee is bound by license condition to track the amount of radioactivity they possess, confirm it is all present and accounted for on a regular basis, and demonstrate they have control over it whenever challenged by their regulators. It might make for a good novel if a university was a bit lackadaisical with their radioactivity, but in reality few are. Those that do slack off a bit are quickly reigned back in.

Q# 27: We manufacture a radioiodine decontamination agent that has been very effective commercially now for 30 years in binding and containing isotopes of iodine, preventing sublimation and facilitating waste water disposal. The usual decontamination agents rely on chelators and alkaline solutions to remove contamination which only serves to drive radioiodine into the gaseous state. How similar is F-18 to radioiodine and what happens when F-18 is subjected to the chelating/alkaline decontamination reagents? Should we pursue an investigation of the use of our product, I-Bind (reflexindustriesinc.com) for this radioisotope? How would you recommend we proceed? I trained and got certification as a NM(ASCP) back in the early 1970’s but I have lost touch with the Nuclear Medicine discipline. Any guidance you could provide would be most appreciated as my wife and I now operate a (wait for it) Ma and Pa business now in our senior years. (5/5/11)

Date: May 5, 2011

Answer: We love hearing about “Ma and Pa” businesses and we sure do wish you and your business a lot of luck. Decontamination reagents are always in vogue in this business, and everyone is always looking out for the latest rage.

Your interest as expressed in your question relates to the chemical properties of the material called fluorodeoxyglucose, commonly abbreviated FDG. When the radioactive isotope Fluorine-18 (F-18) is used, FDG becomes a radiopharmaceutical used in the medical imaging modality of positron emission tomography (PET). Chemically, it is 2-deoxy-2-(18F)fluoro-D-glucose, with the positron-emitting F-18 substituted for the normal hydroxyl group in the glucose molecule.

With that said, this CHP in particular can give you lots of information on the isotope F-18, including decay states, human metabolic information and other radiation-related things, but I’m afraid my expertise doesn’t extend to whether your decontamination agent is capable of binding the molecule in question or not. That chemistry question might be best answered after some bench studies using a non-radioactive form of FDG.

We do want to be sure you know an important fact about the radioactive form of FDG. The isotope F-18 has a physical half-life of only 110 minutes. Therefore, most facilities that use this compound don’t bother with decontamination agents after a spill or contamination event. They merely secure the area for a day and then go right back to work after the isotope has fully decayed. Unless you know of a speciality purpose, we’re guessing there might not be much of a demand for F-18 decontamination agents in light of the fact that half-life will do the trick relatively quickly.

We are pleased to hear that you have come up with an approach that binds radioiodine rather than creating a more volatile version. Volatile isotopes of iodine create a much greater personnel exposure potential, thus your solvent sounds like it might be of interest to hospitals and others that do radioiodination work.

Q# 28: I just tried a new dentist’s office which I like very much but the office layout seemed like it could expose you to other people’s x rays. There are three dental chairs/individual ‘room’ in this office side by side. Each ‘room’/chair has its own x ray machine. I put ‘room’ in quotes because they aren’t really rooms at all since they do not have individual doors or ceilings. There’s just a wall separating each ‘room’ (and the walls of each room don’t even reach the ceiling.) So there is really nothing enclosed. It’s more like an open-air office with partitions separating each dental chair and x ray room, that’s it. They also use digital x rays. Is this safe when I am getting my teeth worked on in one room and there are x rays being taken right next to me, or if I’m walking down the hall and someone’s getting an x ray as I pass by? (5/24/11)

Date: May 24, 2011

Answer: Dental x-ray procedures have definitely come a long way since the first uses of x-irradiation in the 1920’s. X-rays constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics”section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

Many years ago, dental x-ray equipment was a lot less sophisticated than it is today. Not only that, the type of film used was much slower than that in use now. As a result, radiation protection professionals practicing back in the early 1950’s found that radiation doses from full-mouth diagnostic exams being performed in their day could be substantially reduced by placing a leaded apron over the patient. You might remember those, I suspect. The technological improvements in equipment, film types and sensors (for digital x-radiography) in use today have pretty much eliminated the need for leaded aprons. On the other hand, patients often expect to have an apron placed over them during their procedures, just because they were used to seeing them in the past. Therefore, many dentists even today continue to offer the use of leaded aprons to their patients simply to ease their concerns.

With that said, let’s take a look at where the radiation goes when a dental x-ray procedure is performed. X-ray machines in dentists’ offices are highly collimated, meaning the x-ray beam is pretty tightly focused on where the film or imaging sensor is placed in the patient’s mouth. Collimation serves two purposes; it ensures the proper amount of x-ray energy – no more, no less – is available to produce the image, and it keeps scattered x-rays that add nothing to the quality of the picture from irradiating the patient.

What does collimation have to do with your question? If you happened to sit outside of the “line of sight” of the x-ray tube in the little room right next to yours when that patient’s x-rays were being taken, you received little, if any, radiation exposure at all. In fact, the patients themselves only incurred a radiation dose in the general area of the film/sensor and not to the rest of their bodies. What’s more, the dose at that location was too low to result in any sort of demonstrable health effects. (For more information on typical dental x-ray exposures and how they compare to the risks of radiation-related health effects, we invite you to visit the Plexus-NSD web page under the “Tool Box” and the “Radioactivity Basics” sections.)

While the layout of your new dentist’s office might seem unusual to you, keep in mind that doctors and dentists who have been given a permit to operate diagnostic x-ray machines have a legal obligation as well. In order for your dentist to have received a permit to operate the dental x-ray units in the office, he or she had to assure the state regulatory agency that no member of the general public and no employee would receive a radiation dose in excess of the applicable legal dose limits. Those dose limits are set so low that even if someone reached the limit, no demonstrable radiation-related health effects would result. You might want to talk about this issue with your dentist, who should be able to reassure you about the safe operation of the diagnostic devices he owns.

The manufacturers of the equipment that your dentist is using provided him with information on how to set up their office and operate their x-ray machines in order to meet all regulations and requirements. Therefore, even though it might make you wonder about the practice you are observing at your new dentist’s office, let me reassure you that the x-rays being produced during each procedure are highly focused and there is little, if any, scattered radiation. Therefore, the nearby patients and office workers are not receiving unnecessary radiation dose.

On a final note, as a patient, we definitely recommend you exert your rights whenever possible. You should pose this very question to your dentist during your next scheduled visit. They should be able to put their radiation-related procedures into perspective and will be able to reassure you that you are not being unnecessarily exposed when nearby patients undergo their own procedures. A dialogue of this nature will be helpful in easing your anxieties and it might give you something to talk about with the new dentist.

Q# 29: I am a 35 year old female. I had a lumbar spine and sacrum x ray done where 8 pictures were taken and I haven’t been able to stop worrying since. I had the x ray done because I was experiencing a sore tailbone without any known injury and my dr. recommended it as we were ending our visit, almost as an after thought. I asked isn’t the radiation a concern and she said na. I went back and forth with myselft because I didn’t want to get it, but my soreness would come and go and I was also worried about that. I finally got the x ray and I instantly regretted it and was so worried about the effects of the radiation on my reproductive organs, blood, bone marrow, and tyroid. I am very worried because none of my organs were covered. I know that I have follicular cysts on my ovaries and I’m worried they may turn into cancer. I know that the lumber spine plus the sacrum x rays have the same amount of radiation that we receive naturally in about a half of year. I’m worried if this will greatly increase my risk to cancer getting a 1/2 of years worth of radiation in one sitting. In addition, after the xray my sore tailbone went away for about 2 weeks, but now it is back. Nothing abnormal showed up on the x ray…. frustraiting any suggestions on that too! (6/3/11)

Date: June 3, 2011

Answer: Let me give you the short answer right now as it is clear you are worried about your recent radiological experience . . . please don’t worry further about the radiological ramifications associated with the procedure because they will not result in any demonstrable health effects. Your big worry right now should be whether your condition was adequately diagnosed and if you will be on the road to recovery soon. With that said, let me fill in some gaps.

Diagnostic x-rays are probably the most commonly employed form of radiology, a science that uses imaging techniques to allow doctors to see inside a patient’s body (i.e., broken bones). However, the number of x-rays you have had over the years has been and will continue to be determined by your physicians. As you know, these professionals take ethical vows to administer only those procedures that are deemed necessary to diagnose the patient’s medical situation. The benefits obtained by ordering those procedures by far outweigh the radiological risks associated with them. Can you imagine what your risk would be if your doctor did not have access to or did not use these valuable diagnostic tools? Diseases and adverse medical conditions that are readily treatable when diagnosed reasonably early in their progress could escalate quickly, jeopardizing your health . . . or worse. When one reaches this stage, conventional treatment modalities are often ineffective.

Generally speaking, the amount of radiation exposure you receive during each of your medical procedures really is trivial in light of the amount needed to result in demonstrable radiation-related health effects. There has never been a demonstrable health effect associated with radiation exposures of 10,000 millirem or less. (And in case you were expecting SI units, 10,000 millirem is the same as 0.1 Sieverts, Sv.). And even for acute exposures between 10,000 and 50,000 millirem, (0.1 to 0.5 Sv) the effects are typically small and reversible. (By acute, I mean instantaneously, not over a one-year period. As the exposure duration increases, the body’s ability to repair increases, raising the threshold at which effects can be seen.). It takes very high radiation exposures, much higher than the types you have received to date and expect to receive in the future, for there to be any increased risk of effects (i.e., cancer) above the normal population incidence. (Please visit the “Radioactivity Basics” section of the Plexus-NSD web page, in particular the tutorials on “Basic Concepts”, “It’s Everywhere” and “Radiation Risks”, for more information.)

As a patient, however, we definitely recommend you exert your rights whenever possible, and we strongly encourage you to have your primary care physician keep track of all of your diagnostic procedures, whether they include radiation or not. Your doctor will then know exactly how much radiation exposure you have received over the years, how much is anticipated in the future as they follow your health care, and what the effects, if any, you might incur. If he discusses these numbers with you, both you and your physician can weigh the risks and the benefits before deciding to forgo or delay a recommended procedure. And please do not avoid future radiology procedures for medical or dental diagnosis and treatment simply because of a fear of possible radiation-related health effects. It would be much riskier for you to follow this path than it would be to follow one laid out by your health care professionals who have only you and your well-being in mind.

Q# 30: During my last dental exam I had my entire mouth x-rayed with a ‘digital’ dental x-ray for my six month check up. Afterwards I noticed the lead shield ‘bib’ hanging on a hook on the wall, which I was not offered to wear during the x-rays. Now I am extremely distraught and worried about what my body was exposed to. Every where I have researched my concerns says EVERY patient should be given a lead shield EVERY time. (6/10/11)

Date: June 10, 2011

Answer: Please don’t be distraught or worried. The radiation dose associated with your recent dental visit was far too low to result in any sort of radiation-related health effect. With that out of the way, let me give you some additional information so you will know why we can make that statement with confidence.

Dental x-ray procedures have definitely come a long way since the first uses of x-irradiation, back around the 1920’s. X-rays constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics”section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

While the procedures followed during your last trip the dentist might seem unusual to you, keep in mind that doctors and dentists who have been given a permit to operate diagnostic x-ray machines have an obligation as well. They are required by law to deliver only the amount of radiation necessary to achieve their diagnostic goal, and to ensure the radiation exposure of patients, office workers and pretty much everyone else is maintained “as low as reasonably achievable”. The manufacturers of the equipment that they use provide them with information on how to set up their office and operate their x-ray machines in order to achieve those important safety and regulatory objectives.

Many years ago, dental x-ray equipment was a lot less sophisticated than it is today. Not only that, the type of film used was much slower than that in use now, and a LOT slower than the new digital x-rays. As a result, radiation protection professionals practicing back in the early 1950’s found that radiation doses from full-mouth diagnostic exams could be substantially reduced by placing a leaded apron over the patient.

The technological improvements in equipment, film types and data processing in use today have pretty much eliminated the need for leaded aprons. However, patients often expect to have an apron placed over them during their procedures because they were used to having them in the past. Therefore, some dentists even today continue to offer the use of leaded aprons to their patients simply to ease their concerns.

Let’s take a quick look at where the radiation goes when a dental x-ray procedure is performed. X-ray machines in dentists’ offices are highly collimated, meaning the x-ray beam is tightly focused on where the film or imaging sensor is placed in the patient’s mouth. Collimation serves two purposes; it ensures the proper amount of x-ray energy – no more, no less! – is available to produce the image. It also keeps scattered x-rays that add nothing to the quality of the picture from irradiating the patient or the machine operator.

As a patient, we definitely recommend you exert your rights whenever possible. If you would feel more comfortable wearing a lead apron, and if there is one available in the office, I’m sure the dentist or technician would be glad to put one on you, although it won’t offer any dose reduction of significance. While you’re at it, you may also want to ask them about the x-ray machine that they are using to acquire your images in regard to scattered radiation. It is your dentist’s responsibility to put their diagnostic procedures into perspective for you and to reassure you that you are not being unnecessarily or excessively exposed as a result of those procedures. A dialogue of this nature in the future will go a long way in easing your anxieties, right?

Q# 31: You EASILY have the most informative website about radiation on the internet BY FAR! You blow all the others away, and the reason I know this is because I am very scared of a situation at the dentist I just had this morning so I logged online to see if I can find something to make me feel better and I read tons of information and yours is THE BEST! So I decided to write to you to see if you can ease my worries because I am now extremely distraught and my mind is spinning in circles with fright and I am driving myself nuts with fear! Here is what happened, I had a full mouth series of 18 dental x-rays this morning and three things happened which I am turning to you for your advice and opinions please: 1) First, the black electrical cord of the x ray sensor that was attached to the the computer was laying on my legs.The cord even had a little black box in the middle of it. Does this have x rays in it? If so I think my legs go x rayed! I moved the cord up on top of the lead shield after a little while but several x rays took place while the sensor cord was on my leg! 2) When the x ray tech put the lead vest on me, it kept slipping down a little from my thyroid and chest, so I kept putting my hands and arms outside the the lead vest to pull it up/re-adjust it higher in between the x rays being taken. But I am afraid I may have inadvertently left my hands and arms exposed during the xrays too! In other words I cant remember if I pulled my arms and hands back under the lead sheild each time after re-adjusting it, or if instead I kept them outside the vest, resting on the arm chair rests, exposed to the x rays! Please help me! Can I get cancer now? I am so scared!

Date: April 24, 2016

Answer: Thank you for your positive comment regarding our web site. We sure do appreciate the feedback. We spend quite a bit of time researching the information that we present, so it’s always great to hear that someone appreciates it.

The simplest answer to your questions right from the start, and the best way to begin to address your concerns, is to say the following: Please don’t worry about the health ramifications of the x-ray procedures that you received or observed in action. They are minimal and will not result in any sort of short- or long-term problems for you. However, your questions are definitely ones you should discuss with your dentist, who is in the best position to address them specifically, and who is obliged to have these conversations with you. You are entitled to answers to all of your questions. With that said, let’s see if I can fill in some gaps to perhaps help you with those conversations.

Let’s start first with me reassuring you that the “sensor cord” you refer to in your first question does not contain or emit x-rays. As such, your legs or any other parts of your body that may have been in contact with the cord were not exposed to any sort of ionizing radiation from the cord.

Secondly, let me give you some information about medical and dental x-rays that might help you understand this issue better. X-rays constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics” section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

Let’s now discuss why x-rays are used. As we mentioned, x-rays are a form of electromagnetic radiation, just like light, except they just have a much shorter wave-length. X-rays are a form of “ionizing” radiation which basically means they can penetrate body tissues which is what generally prompts concern. However, it is just this property that makes them important diagnostic tools. They can penetrate soft tissues like skin and gums much more readily than hard tissues like bone and teeth causing different degrees of shadows. The shadows can be captured on film or digital receivers and are called radiographs (x-ray pictures).

X-ray machines in dentists’ offices are highly collimated, meaning the x-ray beam is tightly focused onto the film or imaging sensor placed into the patient’s mouth. Collimation serves two purposes; it ensures the proper amount of x-ray energy – no more, no less! – is used to produce the image, and it keeps scattered x-rays that add nothing to the quality of the picture from irradiating the patient, the x-ray tech, or any other observers. Unless someone or something, such as your arms that you refer to in your question, is in the direct “line of sight” of the x-ray beam, that item receives very little radiation exposure, if any at all. In most cases, a foot or less is all that is needed to reduce the exposure rates to “background” levels.

Because today’s x-ray machines and image capturing techniques are so sensitive, the amount of radiation needed for diagnosis is negligible, and is almost next to nothing compared to what you get from every day normal natural background radiation. Diagnostic x-rays are still probably the most commonly employed form of radiology, a science that generally speaking, uses imaging techniques to allow doctors and dentists to see inside a patient’s body. However, the number of x-rays people need is determined by physicians or dentists. As you know, these professionals take ethical vows to administer only those procedures that are deemed necessary to diagnose the patient’s medical situation.

There has never been a demonstrable health effect associated with radiation doses below 10,000 millirem. And even for acute doses between 10,000 and 50,000 millirem, the effects are typically small and reversible. It takes very high radiation exposures, a whole lot higher than those associated with dental exams, for there to be any increased risk of effects (i.e., cancer) above the normal population incidence. For comparison, let’s take a look at some typical doses from dental procedures.

Dental radiographs are completely safe, with the average single digital periapical film (peri-around, apical-root end of a tooth) having a dose of approximately 0.1 millirem. For four bitewing radiographs, traditionally used to image the back teeth for decay (the little tabs you bite on are called bite-wings), the dose potential is about 0.4 millirem. As I said above, the x-ray machines take images of only the necessary structures, so there is no scatter of the x-rays to other tissues. Your dentist may even take the precaution of making you wear a lead apron to shield the rest of your body. In fact, the patients themselves receive their radiation dose in the general area of the film/sensor and not to the rest of their bodies. And even at the imaging location, the dose received is far too low to result in any sort of demonstrable health effects. (For more information on typical medical and dental x-ray exposures and how they compare to the risks of radiation-related health effects, we invite you to visit the Plexus-NSD web page under the “Tool Box” and the “Radioactivity Basics” sections.)

Once again, as a patient, we recommend you and all of your family members exert your rights whenever possible. Consequently, you should feel comfortable about posing your questions and any you might have during future radiology procedures to your health care professionals whenever the opportunity arises. They are the only ones who know you’re the details of the equipment they are using and are thus prepared to not only provide you with the answers that you seek, but to put everything into perspective in light of your specific medical condition. You are entitled to answers to all of your questions, even for something as routine and as “low dose” as a dental x-ray. Specifically, if a dentist elects to have multiple x-ray machines in one room and within a few feet of each other, he or she needs to be prepared to explain what, if any, impacts the operation of those machines has on bystanders.

Above all, you should not avoid future radiology procedures for medical or dental diagnosis and treatment simply because of a fear of radiation exposure. It would be much riskier to lose the benefit of these important diagnostic tools than to incur the trivial radiation exposures associated with them. Your health care professionals have your best interests at heart. Please don’t worry about your recent visit to your dentist!

Q# 32: Greetings, On this page: http://www.iem-inc.com/information/tools/specific-activities. The specific activity value for Carbon 14 is given as 4.6 curies per gram. Most of the other sources I find list it as 4.46 curies per gram. Is 4.6 curies a newer value, or is it a typo?

Date: March 7, 2016

Answer: You sir, have one good eye! The values for specific activity shown in the “Tool Box” section of the Plexus-NSD web page were taken from a combination of resources. Many are from Table A-1 of Title 10, Code of Federal Regulations, Part 71 (10 CFR 71), Appendix A. Others we calculated ourselves using reference values for half-life and the known specific activity of Radium-226 (Ra-226).

After we received your inquiry, we went back to both approaches, and sure enough, the specific activity of Carbon-14 is 4.5 curies per gram. As much as we try to convince ourselves that we are perfect, the web page did indeed contained a typo. It has been duly corrected, and we thank you very much for calling it to our attention!

Q# 33: Please I’d like to know the Gamma Factor for Ir-192 in micro sievert -m2 / (MBq-h).

Date: February 11, 2016

Answer: Fortunately, the answer to your question is available on the Plexus-NSD web site at http://www.iem-inc.com/information/tools/gamma-ray-dose-constants. However, the result given for Ir-192 of 0.59163 is in units of Rem per hour at a distance of one meter from a one curie source, so we now need to go through a simple conversion of units.

To do that, you will need to know how many milliseverts (mSv) there are in a “rem”, and how many megabecquerels (Mbq) in a millicurie. It is also important to remember that you can multiply anything by one (unity) and not impact the accuracy of the result. With that said, let’s see if we can’t convert the web page result into the units you are wanting by doing nothing more than multiplying it by one a few times.

Let’s start first with a simple conversion of rems to Sv. We know there are 100 rem in each Sv, therefore, if I divide one 100 rem by 1 Sv, the answer is one. Right? If you agree with that, then I can multiply rem/hr by one (unity) any time I like, right? In that case:

0.59163 rem/hour per meter-curie x 1 Sv/100 rem = 0.0059163 Sv/h per curie per meter

Let’s do it again, but this time we’ll multiply our result by another unity relationship of one Sv being equal to one million, or 1E6 microSv:

0.0059163 Sv/hr per meter-curie x 1E6 microSv/Sv = 5,9163 microSv/hr per curie per meter

We’re getting closer! Now we’ll multiply the result by one again using the relationship of 3.7E10 Bq being equal to one curie, then by the unity relationship of one MBq being equal to 1E6 Bq, which brings us to the following:

5,9163 microSv/hr per curie per meter divided by (1 curie x 3.7E10 Bq/Ci x 1 Mbq/1E6 Bq) = 1.6E-01 microSv/hr per MBq per meter. And there you have it!

Q# 34: Hello, your website is very informative and answers many good questions. I think I have some misconceptions about naturally-occuring and man-made radiation. I have a few questions I have been wondering about. 1) With naturally-occuring radiation, such as the type in bananas or brazil nuts, can the radiation be spread by touching them or walking near them? For instance, can you or your clothes become contaminated by walking past a large amount of these items in the grocery store or handling these items? Does anything remain on your hands after touching a banana that could be spread around? 2) After you eat these types of food, can you cough any radiation out or is it absorbed by your body? Wondering if anything lingers or if you could spread to someone else? 3) If a ceiling fan were running in your kitchen could the radiation from certain food items like bananas blow around the room and contaminate anything? Also wondering about the fan and the smoke alarm. Could anything harmful blow out of the smoke alarm by being near a fan? 4) With the naturally-occuring radiation in brick floors, patios, etc. is it dangerous to sit down a bag of groceries on the bricks? Can the bricks contaminate anything or absorb into the items? I recently purchased some toiletries at the store and was wondering if the bricks could cause any harm or transfer anything to these items by being near them. 5) If a bottled or canned beverage is placed on a smoke alarm is it safe to drink? 6) Can you trap / contain electromagnetic radiation between two things? I was hanging wallpaper recently and the step ladder I was standing on was sitting almost on an electrical radio cord. Could anything get trapped between the wall and the wall paper from the field of the cord? 7) I have read that during the normal operating conditions of a nuclear power plant, some controlled emissions are released. Could these type of emissions get on your vehicle / clothing etc. and be spread around, if you were in their vicinity? I have a fear of driving past these facilities, due to lack of understanding. Thanks so much for your assistance and clarification. I am not looking for any super technical answers, just some basic understanding. (7/28/15)

Date: July 28, 2015

Answer: Thank you very much for your nice comments about the Plexus-NSD web site. We’re glad you discovered it and we hope it will not only be useful to you, but that its user-friendly as well. Now let’s get right to your questions regarding naturally-occurring and man-made radiation. I’ll list them again and then provide my response.

1) With naturally-occurring radiation, such as the type in bananas or brazil nuts, can the radiation be spread by touching them or walking near them? For instance, can you or your clothes become contaminated by walking past a large amount of these items in the grocery store or handling these items? Does anything remain on your hands after touching a banana that could be spread around?

Response: Most if not all of the naturally-occurring radioactive elements that are present in these food products are not readily transferred from the food stuff to your skin or clothes. The amounts of radioactivity in bananas and brazil nuts are very small and do not pose a health risks. In fact, for many people, both of these food stuffs are essential parts of their healthy, daily dietary intake. The amount of external radiation that is emitted from these items is very small and almost impossible to detect with a radiation survey meter. Walking past them in the grocery store does not pose a radiation risk.

2) After you eat these types of food, can you cough any radiation out or is it absorbed by your body? Wondering if anything lingers or if you could spread to someone else?

Response: Following ingestion, a fraction of the naturally-occurring radioactive elements contained within these food stuffs are absorbed by the body’s tissues and then excreted over time. The other fraction that is not absorbed by the body is excreted shortly after intake. Excretion of these naturally-occurring radioactive elements is primarily through a person’s urinary and digestive systems. Please keep in mind that the amounts of radioactivity in these food stuffs do not pose a radiation risk and are so small that it requires special radiochemical analysis at a certified laboratory to even detect and quantity the small amounts that are present. I also want to point out that a small fraction of potassium that is naturally present in human tissue and essential to life and our circulatory system (e.g., healthy heart) is radioactive and is called potassium-40 or K-40 for short. This is the same K-40 that is found in bananas and other food products. Suffice it to say that humans, other living creatures, and plants present here on good-old mother earth are naturally radioactive and their survival as a species has been impressive.

3) If a ceiling fan were running in your kitchen could the “radiation” from certain food items like bananas blow around the room and contaminate anything? Also wondering about the fan and the smoke alarm. Could anything harmful blow out of the smoke alarm by being near a fan?

Response: The short answer to both parts of your question is “no”. As mentioned in my reply to your earlier question, the radioactive elements in a banana are mostly fixed within the food stuff fibers and are not available to become airborne under normal conditions of human consumption. The radioactive element present in smoke detectors is safely encapsulated and under normal conditions are not released from the smoke detectors and thus not available for dispersal by a nearby fan.

4) With the naturally-occurring radiation in brick floors, patios, etc. is it dangerous to sit down a bag of groceries on the bricks? Can the bricks contaminate anything or absorb into the items? I recently purchased some toiletries at the store and was wondering if the bricks could cause any harm or transfer anything to these items by being near them.

Response: The answer to this one is also “no”. Natural radioactivity in brick and patio materials is normally fixed within the material, and under normal use conditions is not available to be transferred to an object that comes in contact with these building materials. Again, the amounts of natural radioactivity in these materials do not pose a radiation risk and are so small that it requires special radiochemical analysis at a certified laboratory to detect and quantity the amounts that are present.

5) If a bottled or canned beverage is placed on a smoke alarm is it safe to drink?

Yes, it is safe for you to drink that beverage since the radioactivity is contained within the smoke detector and is not transferred to the beverage under normal conditions.

6) Can you trap / contain electromagnetic radiation between two things? I was hanging wallpaper recently and the step ladder I was standing on was sitting almost on an electrical radio cord. Could anything get trapped between the wall and the wall paper from the field of the cord?

Response: The type of electric field and radiation you refer to in your question, known as radiofrequency radiation or RF, is called non-ionizing radiation. RF can be slowed down or absorbed by the wall and/or wallpaper but it does not pose a health risk. Once absorbed or “trapped” as you say, the energy is reduced or eliminated. In general, studies have shown that environmental levels of RF energy routinely encountered by the general public are far below levels necessary to produce any adverse effects. However, there may be situations, particularly workplace environments near high-powered RF sources, where recommended limits for safe exposure of human beings to RF energy could be exceeded. In such cases, restrictive measures or actions may be necessary to ensure the safe use of the RF-generating devices. More importantly, I would suggest not placing the ladder on the electrical cord as there is a chance the outer insulation could be damaged which could create an electrical shock hazard. Also, be careful about where you position your ladders in the future as we also wouldn’t want you to fall.

7) I have read that during the normal operating conditions of a nuclear power plant, some controlled emissions are released. Could these type of emissions get on your vehicle / clothing etc. and be spread around, if you were in their vicinity? I have a fear of driving past these facilities, due to lack of understanding.

Response: The amount of radioactivity released from a nuclear power plant is exceedingly small and does not pose a risk to public health. On average, Americans receive a radiation dose of about 0.62 rem (620 millirem) each year just by virtue of being alive. Half of this dose comes from natural background radiation, with most coming from radon in the air and lesser amounts from cosmic rays and the Earth itself. The other half (310 mrem) comes from man-made sources of radiation in the form of medical procedures, with much smaller amounts come from commercial and industrial sources. An annual radiation dose of 620 doesn’t cause any demonstrable health effects, so the annual radiation dose associated with living near a nuclear power of 0.0009 millirem per year presents no risk. In fact, the radiation dose to a person living within 50 miles of a coal-fired electrical utility plant is about 0.03 mrem due to the natural radioactive found in coal, so the dose potential is higher from a coal-burner than a uranium-burner!. If you are interested, I refer you the following U.S. Nuclear Regulatory Commission website link which contains a personal dose calculator that you can use to determine your annual radiation dose: http://www.nrc.gov/about-nrc/radiation/around-us/calculator.

Q# 35: First off, Thank you Plexus-NSD for a great website. The questions I have surrounds that of specific activities (SA) and uranium. I notice that the SA you have listed for u235 is 2.1e-6 Ci/g and the SA you have listed for 95% enriched is 9.1e-5 Ci/g can you please elaborate on this? I am well aware that DOE has used different methods of enrichment. The only logical reason for those different methods were employed were gains in efficiency (g/$) This in theory would directly affect the % u235 in depleted uranium. So therefore I think I would not be out of line to ask you where you got your SA of uranium. Thank you for your time.

Date: April 6, 2015

Answer: Thank you very much for your nice comments on the Plexus-NSD web site. We’re glad you discovered it and we hope it will not only be useful to you but that its user-friendly as well.

Now let’s get right to your question regarding specific activity of uranium. Before we respond on how the values that appeared on our web site listing (http://www.iem-inc.com/information/tools/specific-activities) were derived, let’s review a few basic concepts. Specific activity pertains to the relationship between the mass of a given radioactive material and its activity or rate of decay. Typical units for specific activity here in the US are the number of curies (Ci) per unit mass (g). In other countries you will see specific activity stated in units of becquerels per kilogram (Bq/kg).

Digging down further into basic concepts, the curie (Ci) is defined as the activity of one gram of Radium-226, in which 3.7E10 atoms are transformed per second, or often referred to as disintegrations/second (d/s). (If you are interested in learning more about the units of radioactivity, go to the “Reference Directory” – “References and Resources” section of the iem web site.) Therefore, the specific activity of any carrier-free radionuclide (i.e., one that is not mixed with any other isotopes or elements) can be calculated by taking advantage of the fact that there are 3.7E10 transformation per second in a gram of Ra-226 as follows: SAi = (226 x 1600) divided by (Ai x T1/2i), where Ai is the atomic weight of the radionuclide in question, T1/2 is the half-life of the radionuclide in year, and 1600 is the half-life of Ra-226 in years. (Let me apologize for the difficulty in writing equations for e-mails.) While you can try using this equation to derive the specific activity for any uranium isotope you like, most people find it easier to use published reference values that have been reviewed and confirmed (technical- and quality-checked) by qualified professionals.

Now let’s move on to the topic of specific activities for uranium isotopes and isotope mixtures. Those isotopes – along with their half-lives in years – that are the main contributors to the alpha radioactivity of uranium include U-238 (4.47E9 years), U-235 (7.03E8 years), and U-234 (2.445E5 years). The specific activities for U-238, U-235, and U-234 can be found on the Plexus-NSD web site, as you mentioned, and in Title 10, Code of Federal Regulations, Part 71 (10 CFR 71), Table A-1. As it turns out, the values are 3.3E-7, 2.1E-6, and 6.2E-3, respectively. As you can see, the shorter the half-life, the higher the specific activity.

The formula for calculating specific activity from various amounts of U-235 present in the mixture (i.e., enrichments), is not only complicated, it depends on the enrichment technology. Generally speaking, the specific activity increases as the enrichment increases, but not because of the replacement of some of the U-238 with U-235. Instead its due to the increase in the amount of U-234. Gaseous diffusion, the primary technology used in past by U. S. Department of Energy to enrich uranium, and that is now the source for much of the depleted uranium generated in the U.S., causes an even greater increase in U-234 when compared with the increase in the U-235 content. For example, when the U-235 content is increased from 0.72% (natural) to 2.96%, an approximate four-fold increase, the U-234 content increases from 0.006% to 0.03%, which is a five-fold increase. This is why the specific activity for 95% enriched uranium is greater than that of pure U-235. Interesting, no?

Once again, this situation doesn’t necessary apply to other enrichment technologies that may be in use today or that are under development. Other technologies, such as centrifuges, have been shown to be more cost effective, which is why gaseous diffusion has fallen out of favor as the enrichment method of choice. And here’s another interesting tidbit . . . depleted uranium contains less than 0.3% or less of U-235 by weight. However, what’s interesting is that this definition is irrespective of the enrichment technology used to separate the isotopes of uranium to the desired level of enrichment.

If you want to learn more about this topic, there are a several textbook including “Introduction to Health Physics” by Herman Cember or “The Atomic Nucleus”, by Robley Evans that are excellent resources. Be forewarned, however, that neither are light reading! However, they should both be available in any technical or university library.

The bottom line is that you can calculate specific activities for uranium mixtures yourself, although this can be tedious. You can also look them up on the Plexus-NSD web site, or you can get yourself a copy of 10 CFR 71, Table A-1 and A-4. However, don’t overlook the confounding factor of enrichment technologies!

Q# 36: “Well I am very scared for both me and my 18 year daughter! Today I just took my daughter to the dentist. She only turned 18 yesterday so she still sees a pediatric dentist. She (my daughter) got 2 cavities filled while I waited in the waiting room. After she got the cavities filled, the dentist called me in from the waiting room to talk to her (the dentist) and my daughter in the hallway of the dentist office. The three of us had a little meeting there as we stood and talked about the cavities my daughter just had filled and all that…basically the dentist was just debriefing me about the appointment my daughter just had. but as we were standing there talking we were only about 3 or 4 feet from a row of kids in dental chairs having one x ray after another! I know this because I watched it happen! about 4 kids each got 6 x rays or so and we were within arms reach of all them and the weird thing is the dentist just kept talking to us seemingly oblivious to the fact these x ray machines were going off right and left like we were in the middle of a freaking war zone! I am so scared now that I and my daughter each got unnecessary radiation exposures especially because we’ve both had lots of X rays in our lives. I just couldn’t believe the dentist asked us to have this little meeting with her right there next to the live x rays going on over and over! when our meeting was over I guess I was just too shocked to ask the dentist what was going on, so I asked the receptionist about whether this was just standard procedure to shoot x rays with people standing right by the machines like this and she told me not to worry and that we were far enough away from the machines and we get more radiation being in the sun all day. I am so scared! Should I be worrying about cancer from all these x rays I got but I didn’t really get! Thank you!”

Date: November 19, 2014

Answer: The simplest answer is the best way to start in trying to address your concerns. Please don’t worry about the health ramifications of the x-ray procedures that you or your daughter received or observed in action. They are minimal and will not result in any short- or long-term problems for you. However, your questions are definitely ones you should discuss with your dentist, who is in the best position to address them specifically, and who is obliged to have these conversations with you. You are entitled to answers to all of your questions. With that said, let’s see if I fill in some gaps.

First let me give you some information about medical and dental x-rays that might help you understand this issue better. X-rays constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics” section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

Diagnostic x-rays are still probably the most commonly employed form of radiology, a science that generally speaking, uses imaging techniques to allow doctors and dentists to see inside a patient’s body. However, the number of x-rays people need is determined by physicians or dentists. As you know, these professionals take ethical vows to administer only those procedures that are deemed necessary to diagnose the patient’s medical situation.

Generally speaking, the amount of radiation dose received during a typical dental procedure (i.e., a few millirem at the most) is trivial in light of the amount needed to result in demonstrable radiation-related health effects. There has never been a demonstrable health effect associated with radiation exposures below 10,000 millirem. And even for acute exposures between 10,000 and 50,000 millirem, the effects are typically small and reversible. It takes very high radiation exposures, a whole lot higher than those associated with dental exams, for there to be any increased risk of effects (i.e., cancer) above the normal population incidence.

Now let’s take a look at where the radiation goes when a dental x-ray procedure is performed. X-ray machines in dentists’ offices are highly collimated, meaning the x-ray beam is tightly focused onto the film or imaging sensor placed into the patient’s mouth. Collimation serves two purposes; it ensures the proper amount of x-ray energy – no more, no less! – is used to produce the image, and it keeps scattered x-rays that add nothing to the quality of the picture from irradiating the patient, the x-ray tech, or observers.

What does collimation have to do with your question? Unless someone or something is in the direct “line of sight” of the x-ray beam, that item receives very little radiation exposure, if any at all. In fact, the patients themselves receive their radiation dose in the general area of the film/sensor and not to the rest of their bodies. As mentioned above, the dose at the imaging location itself is far too low to result in any sort of demonstrable health effects. (For more information on typical medical and dental x-ray exposures and how they compare to the risks of radiation-related health effects, we invite you to visit the Plexus-NSD web page under the “Tool Box” and the “Radioactivity Basics” sections.)

As the receptionist in your dentist office explained, distance also plays a role in reducing whatever scattered radiation might be present to a negligible amount. In most cases, a foot or less is all that is needed to reduce exposure rates to “background” levels.

Once again, as a patient, we recommend you and all of your family members exert your rights whenever possible. Consequently, you should feel comfortable about posing your questions and any you might have during future radiology procedures to your health care professionals whenever the opportunity arises. They are the only ones who know you’re the details of the equipment they are using and are thus prepared to not only provide you with the answers that you seek, but to put everything into perspective in light of your specific medical condition. You are entitled to answers to all of your questions, even for something as routine and as “low dose” as a dental x-ray. Specifically, if a dentist elects to have multiple x-ray machines in one room and within a few feet of each other, he or she needs to be prepared to explain what, if any, impacts the operation of those machines has on bystanders.

Above all, you should not avoid future radiology procedures for medical or dental diagnosis and treatment simply because of a fear of radiation exposure. It would be much riskier to lose the benefit of these important diagnostic tools than to incur the trivial radiation exposures associated with them. Your health care professionals have your best interests at heart.

Q# 37: There are several facilities for performing medical tests that use radioactive isotopes. recently some other non radioactive method have been found and become commercial that can give the same results with better accuracy or even the same, such as using C-13 UBT instead of C-14 UBT. If we continue to use the radioactive method, dosen’t it against ALARA?

Date: October 31, 2014

Answer: You’ve asked an interesting question. Before we get to an answer, let’s do a quick review of the ALARA concept.

“ALARA”, an acronym for “As Low As Reasonably Achievable”, is a basic radiation protection concept or philosophy. It is an application of the “Linear No Threshold Hypothesis,” which assumes that there is no “safe” dose of radiation. Under this assumption, the probability for harmful biological effects increases with increasing radiation dose, no matter how small. It follows then, to ensure affected populations are protected, that radiation doses are ALARA.

Back in the 1950’s, the Atomic Energy Commission, now called the Nuclear Regulatory Commission (NRC), promulgated occupational exposure regulations based upon that same assumption that there was no threshold for radiation-related effects, and that the response was linear all the way down to “zero dose”. The NRC’s rules have changed over time, mostly with respect to how to measure dose and how to limit exposure, but the occupational limits themselves have remained fairly static. The law clearly states that licensees must maintain occupational radiation exposures from internal deposition and external exposure combined, to less than 5,000 millirem over a year, and general public exposures to less than 100 millirem per year. However, the law also states that exposures must also be ALARA.

Here’s the exact wording: In Title 10, Code of Federal Regulations, part 20.1101(b) (10 CFR 20.1101(b)) states that licensees “shall use, to the extent practical, procedures and engineering controls based upon sound radiation protection principles to achieve occupational doses and doses to members of the public that are as low as is reasonably achievable.” However, if you look at 10 CFR 20.1301(a)(1), it states that these limits exclude medical administrations.

Hospitals, imaging centers and other facilities that treat or diagnose patients need to comply with the very same dose limits and ALARA requirements as any other licensee to ensure the risks of working at or living nearby their facility is no greater than working at or being near any other safe industry. However, the regulatory dose limits don’t apply to patients. In order to obtain the benefit of a particular diagnostic or treatment, doses in excess of the general public or occupational limits are usually required. It is up to the physician and/or radiologist, not the NRC, to determine what radiation dose is needed in order to maximize the benefit to the patient.

The NRC and Agreement States do, on the other hand, does have rules for ensuring physicians making those decisions are qualified to do so, and that the hospital or diagnostic facilities providing radiation-related services have procedures in place to keep from delivering unnecessary radiation doses. There is also a push within the radiation protection community to “image gently”, particularly when it comes to diagnosis or treatment of infants and children (see http://www.imagegently.org). While I am not well-versed on the specific applications or possible clinical limitations for each of two diagnostic methods you point out in your question – “C-13 UBT” vs. “C-14 UBT” – I am certain that the rules that govern the medical use of radioactive materials are designed to minimize risk to the patient provided those decisions and choices made by medical professionals result in a net benefit to the patient.

The bottom line is that the ALARA concept, as codified in federal and state standards for protection against radiation, applies to occupational workers and members of the public, exclusive of medical exposures. However, radiation protection professionals, medical physicists, and physicians qualified to diagnose or treat patients are strongly encouraged to be sure patient exposures are necessary, justifiable, and optimized. That sounds a lot like ALARA, doesn’t it? To learn more, I would direct you to review Title 10, Code of Federal Regulations, part 35 and related guidance documents for best practices used by medical professionals.

Q# 38: I wanted to know about the ALARA concept, was it specifically designed to protect the patients or both radiation workers and patients?

Date: October 2, 2014

Answer: You’ve asked an interesting question, that’s for sure. Before we get to an answer, let’s do a quick review of the ALARA concept.

“ALARA”, an acronym for “As Low As Reasonably Achievable”, is a basic radiation protection concept or philosophy. It is an application of the “Linear No Threshold Hypothesis,” which assumes that there is no “safe” dose of radiation. Under this assumption, the probability for harmful biological effects increases with increasing radiation dose, no matter how small. It follows then, to ensure affected populations are protected, that radiation doses are ALARA.

Back in the 1950’s, the Atomic Energy Commission, now called the Nuclear Regulatory Commission (NRC), promulgated occupational exposure regulations based upon that same assumption that there was no threshold for radiation-related effects, and that the response was linear all the way down to “zero dose”. The NRC’s rules have changed over time, mostly with respect to how to measure dose and how to limit exposure, but the occupational limits themselves have remained fairly static. The law clearly states that licensees must maintain occupational radiation exposures from internal deposition and external exposure combined, to less than 5,000 millirem over a year, and general public exposures to less than 100 millirem per year. However, the law also states that exposures must also be ALARA.

Here’s the exact wording: In Title 10, Code of Federal Regulations, part 20.1101(b) (10 CFR 20.1101(b)) states that licensees “shall use, to the extent practical, procedures and engineering controls based upon sound radiation protection principles to achieve occupational doses and doses to members of the public that are as low as is reasonably achievable.” However, if you look at 10 CFR 20.1301(a)(1), it states that these limits exclude medical administrations.

Hospitals, imaging centers and other facilities that treat or diagnose patients need to comply with the very same dose limits and ALARA requirements as any other licensee to ensure the risks of working at or living nearby their facility is no greater than working at or being near any other safe industry. However, the regulatory dose limits don’t apply to patients. In order to obtain the benefit of a particular diagnostic or treatment, doses in excess of the general public or occupational limits are generally required. It is up to the physician and/or radiologist, not the NRC, to determine what radiation dose is needed in order to maximize the benefit to the patient.

The NRC and Agreement States do, on the other hand, does have rules for ensuring physicians making those decisions are qualified to do so, and that the hospital or diagnostic facilities providing radiation-related services have procedures in place to keep from delivering unnecessary radiation doses. There is also a push within the radiation protection community to “image gently”, particularly when it comes to diagnosis or treatment of infants and children (see http://www.imagegently.org).

The bottom line is that the ALARA concept, as codified in federal and state standards for protection against radiation, applies to occupational workers and members of the public, exclusive of medical exposures. However, radiation protection professionals and physicians qualified to diagnose or treat patients are strongly encouraged to be sure patient exposures are necessary, justifiable, and optimized. That sounds a lot like ALARA, doesn’t it?”.

Q# 39: Good Morning- We would like to measure the 8 hour exposure of staff to microwave radiation in our workplace. It is a healthcare industry. What do you suggest to be used as an instrument? Thank you. (9/8/14)

Date: September 8, 2014

Answer: As you suggest in your question, there are indeed many sources of microwaves (i.e., non-ionizing radiation) in the healthcare industry. Most of these are enclosed and well shielded, meaning the exposure potential is minimal, at best. On the other hand, its always a good idea to identify sources so you will have some good information to share if an employee should raise a question.

Before we get to which instrument is best for these measurements, you will first need to determine what frequency of electromagnetic frequency (EMF) radiation you will be measuring. The spectrum of EMF frequencies for microwaves range from 300 megahertz (MHZ) to 300,000 MHZ (300 Ghz), thus it is important to know where you are wanting to measure so you select an instrument that actually responds at that frequency. The manufacturer of the device in question should provide operating frequencies and anticipated power levels in their manuals. (Most manufacturers also post their manuals on-line, just in case you’ve lost one or two.)

What happens if you pick the wrong instrument? You could very well get what appears to be a low reading with that instrument, when in fact there may be significant microwaves present. Avoiding false negatives is the name of the game here.

The next step is to ensure the instrument you select is able to detect a fraction of the occupational exposure limit, meaning less than one (1) milliwatt per square centimeter (mW/cm2). The Occupational Safety and Health Administration (OSHA) limits personnel exposures to EMF with frequencies between 10 MHZ to 100,000 MHZ to less than 10 mW/cm2 in 29 CFR 1910.97, with the power density averaged over a period of six minutes. This limit applies to both whole body irradiation and partial body irradiation. The latter is important because it has been shown that some parts of the human body (e.g., eyes, testicles) may be harmed if exposed to incident radiation levels significantly in excess of the recommended levels.

The final step, once you’ve made all of your measurements, it would be a good idea to document your results so you can readily brief others or even prepare a training module for your hazard communication program. While OSHA does not require a written safety program for sources of EMF, it is always a good idea to tell the staff what you measured and how it compares to the applicable limits. The OSHA web page provides a number of useful resources for use in preparing your training module.

Once you have determined the EMF frequencies of interest in your work place, there are a number of companies that manufacture and sell radiation detection instruments that you can purchase or rent. Without recommending one vendor over another, you may wish to start with Narda Safety Test Solutions (https://www.narda-sts.com/en/) or Holaday (http://www.gigatest.net/holaday.htm), then move on from there.

As a final word, you might want to visit the internet at http://www.physics.isu.edu/radinf/Source.htm, a site maintained by the Idaho State University that contains an extensive amount of radiation-related information. Once at the site, click on “Information on Specific Radiation Sources”, which will take you to the non-ionizing sources, including microwave radiation. And finally, for even more information about this interesting source of non-ionizing radiation, please see the “Links” Section of Plexus-NSD’s web site. There, you will find two particular links: (1) “Non-ionizing Radiation” with a link to the “Microwave News”, which contains more information on microwaves and the instrumentation used to measure them; and (2) the FDA’s web site accessible under the category of “Federal Regulatory Agencies”. Good luck!

Q# 40: How do I convert the mR and R/m to mA (mille Amp) and mAs (mille Amp per second)? (8/5/14)

Date: August 5, 2014

Answer: Your question gives us a good opportunity to review four important physical quantities: mass, length, time, and electric current, the magnitudes and size of which are carefully preserved in standardization laboratories throughout the world. Three of these quantities (mass, time, and electric current) are related to your question and provide us a basis for our response.

However, first some clarification. I assume by referring to “mR” in your question you are referring to milliroentgen, a unit of radiation exposure. Likewise, when you say “R/m”, you mean roentgen per minute. I am not familiar with “mA per second”, so I’m going to assume you meant to state mA-second (mA-s) which describes the current output of an x-ray machine.

We’ll get back to your question shortly, but in the meantime, the units used to describe the aforementioned physical quantities are kilogram (kg), meter (m), second (s), and ampere (A). These units can be used in various combinations to create derived physical quantities that allow us to answer many puzzling questions related to our physical world . . . including your question! At some point, I would encourage you to grab a college physics book and review these in more detail!

The fundamental unit of electrical current is the ampere and it can be used to derive other electrical units in combination with other fundamental or derived units. One of those derived units is charge, which is the product of the current (A) and time (s). Charge is expressed in units of ampere-seconds (A-s), a derived unit, which can be used to calculate the output of a x-ray generator.

Because of the fundamental importance of charge, it is given a special name, the coulomb ©. For many years, and even to this day in the US, radiation exposure has been expressed in units of roentgens ®, where one roentgen is equal to 2.58 x 10-4 coulombs per kilogram (C/kg). This value arises from the fact the roentgen is defined as the radiation energy required to liberate one electrostatic unit (esu) of charge in one cubic centimeter of air, at standard temperature and pressure. Suffice to say, conversion from the electrostatic charge to the coulomb is not straightforward, so I won’t go into it now in the interest of getting back to your question.

But before I do that, let me point out that the International Commission on Radiation Units and Measurements (ICRU) created special units like the roentgen for radiology purposes. Now, however, they recommend phasing them out and using System Internationale (SI) units instead. Unfortunately, habits can be hard to break, so the roentgen and other non-SI units will continue to be used here in the US. We’re not holding our breath waiting for a complete phase out to take place any time soon.

Now let’s get to your question. The simple answer is that converting from mR or R/m to mA or mA-s is not possible without knowing the volume or mass of the material being exposed to the x-ray energy in question, which in this case is air. Nonetheless, the mass or volume can be determined several ways including taking measurements with a properly calibrated standard ionization chamber at the location of interest in air, or by obtaining more information on the operating parameters of the x-ray generating device (e.g., tube voltage, tube current, halve value layer, etc.). Once the “kg” part of the equation is solved, one can theoretically convert from mR or R/m to mA-s/kg, then apply the 1R = 2.5 x 10-4 C/kg conversion factor I mentioned previously.

Let me caution you, however, that many other factors will affect the accuracy of this conversion, thus it is not the preferred approach for getting to the answer. Let me recommend that you gather more information about the operating parameters for the x-ray machine you’re using, and use them to calculate exposure in air, entrance dose to tissue, or any other radiation-related quantity you need.

If you want to learn more about this topic, there are a couple of classic textbooks that do the job nicely. One is “Medical Radiation Physics” by William R. Hendee and the other is “The Physics of Radiology”, by Harold Johns and John Cunningham. Be forewarned this neither of these are light reading, but they do have all of the answers. You can find copies of both tomes in any technical or university library.

Q# 41: I will be having a radio frequency ablation of my saphenous vein soon. What are the risks of the radiation exposure? Should I be concerned? Please be quick with your answer—-I need it in two days. Thank you. (8/6/14)

Date: August 6, 2014

Answer: You know, the first thing that hit me when I received your question is that I wasn’t familiar with the medical procedure you mentioned. Therefore, I did some homework. What I found was that the use of radiofrequency, or “RF” radiation to treat varicose veins is relatively new (i.e., about 15 years old). I also learned that as many as 30% of women and 40% of men had been suffering from the symptoms of varicose veins long before RF ablation hit the streets, with the prior standard of care being surgery that was only marginally successful (i.e., symptoms were likely to return within five years for more than 20% of those treated).

I did some further research and found two interesting articles. One by Dr. Beale and Dr. Mavor, published in 2004 in the International Journal of Lower Extremity Wounds, is entitled “Minimally Invasive Treatment for Varicose Veins: A Review of Endovenous Laser Treatment and Radiofrequency Ablation”. (Int J Low Extrem Wounds. Dec 2004;3(4):188-97). The second, by Dr. Garcia-Madrid and Dr. Manrique, published in 2011 in Cirugía Española (English Edition), is entitled “New Advances in the Treatment of Varicose Veins: Endovenous Radiofrequency VNUS Closure.” (August-September 2011, 89(7):420-426). After reading through them both, I learned that RF ablation systems consist of a catheter that contains an electrode, heated by RF energy, that causes localized heating of the vein wall. The resistance and temperature at the tip of the catheter are monitored during treatment to ensure contact is maintained between the electrode and vein wall, and to ensure the temperature remains constant at 120°C. Here’s the fun part . . . as the vein is denatured by heat, it contracts around the catheter, and voila! And to make things even better, the recovery rate using this technique appears to be quicker than surgery, with improved clinical outcomes.

So now let’s get into an area where us CHPs actually know something; the risk of radiofrequency electromagnetic radiation. RF radiation is composed of electric and magnetic waves that, when in contact with some sort of matter, like water or tissue, cause vibration and friction of their atoms, transforming them into thermal energy (ohmic or resistive heat). Does something about that sound familiar? It should, because that’s also how microwave ovens work!

The principal health hazard associated with RF radiation exposure is heating portions of the body. Those parts of the body that are irradiated but that are not easily cooled by blood flow, such as the lens of the eye, may suffer damage. However, it takes quite a bit of RF radiation to cause these effects, and the damage that is observed is related to “cooking” live tissue. The symptoms of overexposure to microwaves and other RF radiations are nonexistent if the temperature of the exposed tissue is not elevated excessively.

The RF procedure you will soon be having involves non-ionizing radiation with a fairly low frequency. As such, the radiation doesn’t travel very far and will only heat up the location being touched by the electrode. As long as your physician monitors the temperature throughout the process, to ensure it is neither too hot nor too cold, this really is a minimally invasive and safe – from a radiation dose perspective! – procedure for patients. The bottom line is that it sounds like you’ve selected something more effective and with a faster recovery rate than the conventional surgical solution to your vein symptoms. Good luck with your procedure, and we hope you’ll be feeling a lot better very soon!

Q# 42: I have read your CRAZY good website so many times because I have a radiation phobia but I have never asked a question and now I have decided to ask one to get your expert opinion. I hope you can help because I’m riddled with anxiety. I was supposed to have 6 digital dental x rays on my teeth today but I ended up having 7 instead because they told me they needed to retake one since the first one didn’t come out right. So I had an uncessary additional x-ray taken. (Seven x rays rather than six). I am 49 and have lots of problems with me teeth over the years so it seems like I keep getting the same teeth x rayed over and over. I am concerned about the potential radiation effects especially because they are cumulative (unless I’m mistaken) and I also heard of a recent study linking dental xrays to brain tumors. I am freaking out! Can you help me? Did I received too many x rays? I thought digital x rays didn’t require retakes? Can the same tooth be x rayed over and over without getting cancer or a tumor. What should I do? I understand the importance of gettting dental x rays but I don’t want to get too many! Thank you. (7/9/14)

Date: July 9, 2014

Answer: Before we go any further, let me reassure you that its okay for you to have gone through this series of x-rays. The radiation-related risks associated with six or seven digital x-rays is far too low to matter. Now, let me explain myself.

X-rays constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics”section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

Diagnostic x-rays are still probably the most commonly employed form of radiology, a science that generally speaking, uses imaging techniques to allow doctors to see inside a patient’s body. Examples in addition to x-rays include angiography, breast imaging (mammogram), computerized tomography (CT) or “CAT Scans”, magnetic resonance imaging (MRI), nuclear medicine procedures, and ultrasound. However, your interest is x-rays, so let’s just cut to the chase.

The typical radiation dose received from a typical dental x-ray is on the order of two to three millirem per scan. According to one manufacturer of this type of equipment (i.e., AGFA), a digital x-ray delivers up to 60% less radiatio dose to the patient than a conventional film x-ray. Therefore, your exposure potential from a digital system is on the order of one to two millirem per scan. (To learn more about radiation-related units, please visit the “Radioactivity Basics” section of the Plexus-NSD web page.) Those levels are well-within the range of the background radiation dose received by the US population by virtue of being alive, and is far too low to result in any demonstrable radiation-related health effect. For more on that, take a look at the write-ups on radiation risk in the Plexus-NSD web page at http://www.iem-inc.com/information/radioactivity-basics/radiation-risks.

If you’ve browsed your way through the Plexus-NSD web site, you’ve probably also learned that an individual can be exposed to radiation in a variety of ways. These include doses from natural background sources, which in the United States averages about 610 millirem per year for the whole body, but ranges from 400 to over 1,500. (In other parts of the world, it can be significantly higher with no corresponding detrimental health effects). Generally speaking, the amount of radiation exposure a patient receives during procedures like the one you described is trivial in light of the amount needed to result in demonstrable radiation-related health effects. There has never been a demonstrable health effect associated with radiation exposures of 10,000 millirem or less. And even for acute exposures between 10,000 and 50,000 millirem, the effects are small and reversible. (By acute, I mean instantaneously, not over a period of time. As the exposure duration increases, the body’s ability to repair increases, raising the threshold at which effects can be seen.) It takes very high radiation exposures, orders of magnitude higher than those associated with dental diagnostics, for there to be any increased risk of effects (i.e., cancer) above the normal population incidence.

If you would like to learn more about the issue of diagnostic radiology, I suggest you visit the “Radioactivity Basics” section of the Plexus-NSD web site. In addition, you might try to locate a copy of Publication 93 of the International Commission on Radiological Protection in your local techical or university library. Its entitled “Managing Patient Dose in Digital Radiology” (Annals of the ICRP, Elsevier Publications, Oxford, UK, 2004), and it contains a lot of useful information.

Let’s sum up. It sounds like your dentist is using the best available technology to diagnose the condition of your teeth by using equipment that minimizes radiation exposures. However, you should consider talking with your dentist about your concerns. He or she should be able to give you information that is specific to their equipment that will hopefully give you confidence that your exams are safe even if a film or scan needs to be repeated. In any event, declining dental x-rays presents a greater health risk than the x-rays themselves, so please don’t do that. And thanks so much for your very kind comment on the crazy-good Plexus-NSD web site!

Q# 43: Is it possible to diagnose the condensation defect between microwave barrier and door glass? (6/6/14)

Date: June 6, 2014

Answer: That’s a good question! When you see condensation building up on the window of your microwave oven, that sure tells us something is going on.

That little glass window is actually two sheets of glass, with a wire screen sandwiched in between. When the oven was brand new, those layers were all sealed up, and the entire assembly was sealed into the door of the oven. Over time, and with use, sometimes those seals will rupture. When that happens, the steam and water vapor that builds up inside the oven chamber when things are being heated gets trapped in the window assembly because it is no longer “gas tight”.

However, a misty window doesn’t mean those pesky microwaves are escaping from the oven to the outside world. That wire screen will still do its job of keeping microwave radiation from passing through the window. However, if there has been some damage to the oven such that the door or an oven wall are visibly damaged, there could be a gap in the frame, through which the radiation will pass.

The bottom line is that condensation inside of the glass is not a radiation concern. A damaged microwave oven, or a door that doesn’t close tightly should not be used because leakage is possible. If the condensation is bothersome, you might try opening up the door for a bit to let the condensation escape. However, that will only work for a while if the seal around the glass is compromised.

Q# 44: Good morning sir, It is stated that I have taken the radiation conversion factors form the website for inhalation and different other paths. I want to ask that how to find the dose from these conversion factors? I shall be very thankful to you. (5/27/14)

Date: May 27, 2014

Answer: The dose conversion factors that we provide on the Plexus-NSD web page are quite useful. However, it is important that anyone who uses the factors knows where they came from and what their limitations are before relying on them for anything. For example, the “Inhalation Dose Conversion Factors” listed in the “Tool Box” section of the web page came from a compendium prepared by the U. S. Environmental Protection Agency. The basis for those factors is a 1976 model for internal dose limitation prepared by the International Commission on Radiological Protection (ICRP). That is well-and-good for those of us here in the U. S., where our regulatory structure has not kept pace with the rest of the world. However, they would not be appropriate for use in other regulatory environments (e.g., Canada, European Union, etc.)

With that said, the use of the factors is straight forward, so let’s try to do an example. Let’s assume a hypothetical individual has inhaled 50 becquerels (Bq) of Cesium-137 (Cs-137) that is relatively soluble in body fluids, meaning the lung clearance class is “D”. If you go to the “Inhalation Dose Conversion Factors” listing at http://www.iem-inc.com/information/tools/dose-conversion-factors/inhalation, scroll down to the factors for Cesium, and select the value for D-class Cs-137, you can see that it is 31.93 millirem Committed Effective Dose Equivalent (CEDE) for each microcurie inhaled. Therefore, the CEDE to our hypothetical worker, in units of millisieverts, would be calculated as follows: 50 Bq x 0.000027 microcurie/Bq x 31.93 millirem/microcurie x 1 millisievert/100 millirem = 0.000431 millisievert. As you can see, in addition to understanding the basis for the dose conversion factors on the web page, the key to success is being able to convert units correctly!

Q# 45: Hello, great website! I find the information very informative and useful. One question I don’t seem to find a lot of information on is NRC licensing. Do you know if the welding Manufacturer or Distributor I buy my thoriated tungsten electrodes from needs a license to sell them? Someone told me the NRC changed their regulations and now requires a license to sell thoriated tungsten electrodes. According to the manufacturer’s MSDS, the electrodes contain 0.8 -1.2% of 1% Thoriated Tungsten and 1.7-2.2% of 2% Thoriated Tungsten, both noted as Thorium Oxide (ThO2). I’m seeking this information to educate myself so that I can ask my supplier the right questions. Can you please confirm if my supplier needs a license to sell my thoriated tungsten electrodes. Thank you. (05/20/14)

Date: May 20, 2014

Answer: Thanks a million for your kind words on the Plexus-NSD web site. We recently re-launched it and we’re always glad for feedback . . . especially when its good!

With that said, let’s cut to the chase. Your question is really an excellent one. It touches on a topic that has broad-reaching impacts, but many of those that will be impacted the most don’t even know it yet. Fortunately, as a purchaser of thoriated tungsten products, there should only be one impact on you, assuming your suppliers follow the letter and the spirit of the law. Let me go through a few details for you and then I’ll tell you how this will all interfere with your life.

Title 10, Code of Federal Regulations, Part 40 (10 CFR 40), which has been a federal law since the mid-1940’s, currently contains provisions for the licensing and control of thorium and uranium, which are the naturally-occurring radioactive elements present in the aforementioned operations. In that rule, a license is required for possession of anything that contains greater than 0.05% by weight of uranium and/or thorium. However, it also contains some exemptions for specific items, such as optical lenses and, yes, thoriated tungsten products. It also contains an important exemption for possession of small quantities of material.

Until recently, firms that were licensed to manufacture and distribute exempted items – such as thoriated tungsten products! – had no real obligation once the products were released for sale. However, on May 29, 2013, the U. S. Nuclear Regulatory Commission (USNRC) published a final rule in the Federal Register (78 FR 32310) at affected many operations that used to be completely exempt from the requirements of 10 CFR 40. It now requires many of those operations to obtain a specific license in order to possess feed materials and/or distribute products that contain uranium or thorium. It also imposed specific labeling and quality control requirements on the operation and there are a number of new mandated reporting and record keeping steps.

Why the change? Unlike the distribution of other types of radioactivity, 10 CFR 40 didn’t require firms who distribute uranium and thorium to report any information about those distributions. Therefore, the USNRC concluded that distributing this material either to “general licensees” (i.e., those that purchase and use thoriated tungsten products) or to those that are exempt from licensing (i.e., those that never received more than 15 pounds of thorium or uranium) would “significantly increase the NRC’s ability to evaluate impacts and more efficiently and effectively protect the public health and safety from the use of source material”. That conclusion resulted in a significant revision to 10 CFR 40 that becomes effective on August 27, 2014. Here is a brief summary of the salient features of the new rule:

(1) Those that sell products bearing uranium or thorium (i.e., zirconium-based thermal spray powders, thoriated tungsten parts), can no longer do so without having a specific license. Subsequent transfers of these items from exempt person to exempt person, or from general licensee to general licensee, are still okay. However, if one imports “exempt quantity” source material from another country and then distributes it as either exempt or generally licensed, a specific license will be needed.

(2) Any company doing an initial distribution of source material can no longer ship it out the door then forget about it. The new rule requires the company to report activities to the USNRC by January 31st of each year for the previous year’s transfers. Included in the report will be the identity of the distributor, what products, types and amounts of source material were distributed and where they went.

(3) For health, safety and contamination control purposes, after August 27th companies can no longer possess up to 15 pounds of dispersible source material at any one time (or 150 pounds in any calendar year) without having a specific license. The small quantity limits have changed to 3.3 pounds at one time and 15.4 pounds in a year. (Non-dispersible materials still have the 15/150 pound limit but you may not alter the chemical or physical form of the material.) What’s more, the new limit applies to natural uranium and natural thorium only, with no other isotopic mixtures covered.

(4) If one distributes optical lenses coated with thorium, the new rule let’s you keep your exemption and even expands it to include uranium. However, the previous limit on the amount of these elements that can be coated onto lenses will drop by 10%.

(5) Those who manufacture and distribute thoriated tungsten welding rods or similar exempted items can continue to do so under the new rule, but they will need to include safe handling instructions (i.e., MSDSs) that specifically address the radiological hazards of your products.

(6) Glassware containing up to 10% of uranium or thorium by weight, for the purposes of achieving a unique color and glow, used to be exempted in 10 CFR 40. However, the USNRC now considers this to be a frivolous use of source material, thus the new rule drops the limit to 2% by weight.

(7) Some of the items exempted from the requirements of 10 CFR 40 are for products that the USNRC believes to be obsolete (i.e, fire detection units, ceramic tableware). Therefore, they are no longer exempt.

(8) You may no longer abandon source material when you no longer need it, even if it is an exempted or generally-licensed item. If you need to dispose of anything more than 1.1 pounds of non-dispersible source material (i.e., metal brick, alloy, or encapsulated items) in a calendar year, there are a whole other set of requirements that will need to be followed.

The USNRC has concluded that the new rule won’t be burdensome to their constituents, and they are under the impression that the types of records needed to generate their new annual reports are already being kept as part of “business record keeping practices”. They also believe the fees associated with the licensing process are reasonable. However, there are a number of companies who current distribute thorium/uranium-bearing products without a USNRC license that beg to differ. License application fees can range from $2,000 to $10,200, and the annual licensing fees can range from $5,000 to $21,000 . . . and that doesn’t count the cost of preparing the application, developing a management program, and implementing the program. Furthermore, the company may also be subject to decommissioning funding requirements and costs, depending on the type and amount of source material present at the site.

So now you’re up-to-speed with the new laws for possession and distribution of uranium and thorium in things like thoriated tungsten products. For your suppliers, the rule’s impact is likely to be significant, with programmatic changes required at a minimum. Of course, those kinds of changes cost money, so here comes the impact of the new rule on you . . . the cost of your thoriated tungsten products will likely increase.

You might want to inquire about the licensing status of your suppliers just so you can say you did your due diligence. If they look at you with wide eyes and start scratching their heads, point them to 10 CFR 40 and maybe drop a hint that failure to comply could be costly for them. Of course, we wouldn’t mind a bit of you pointed your supplier to Plexus-NSD’s web site before they start scrambling through the internet looking for some assistance.

Q# 46: I recently discovered the house I grew up in had elevated radon levels (birth – 18 years + several months and various visits, so an estimate of 20 years exposure) . . . . 1) Any insight into my actual risk would be greatly appreciated. I also cannot find any people in a similar situation to relate to (or maybe no one worries about it). However, my situation certainly can’t be unique. 2) My doctor has no real recommendations for following up with me (listen to my chest on occasion and address any weird, persistent coughs right away), but if I do get lung cancer, naturally I would want to find it early. I don’t particularly want CT scans (nor do I think I’m really a candidate for them), but any recommendations into how I can be monitored medically would be appreciated. I would hope that an MRI may be an adequate screening tool to minimize radiation exposure, but they don’t seem to be recommended at all for the chest. It seems like they would be more descriptive than a simple x-ray, though, and less descriptive than a CT scan. (03/28/14)

Date: March 28, 2014

Answer: Radon in homes has been studied extensively for many years now. As a result, we have plenty of information on hand to make informed decisions about things like monitoring mitigation and even risk.

As with all homes in the U.S. and throughout the world, radon is a fact of life. The natural radioactivity in the soil releases this gaseous element, thus radon is present in the air we breathe when we are outside, albeit concentrations that are almost too low to measure. However, as soon as you put something on top of the soil to trap the gas – like a home with a basement – radon concentrations start to become measurable. As you have observed, the concentrations inside of homes can vary by quite a bit, from state to state, home to home and day to day within any given home. The question becomes, what does it all mean?

Let’s start out first with some basic information about this naturally-occurring radionuclide. Radon is a radioactive element produced as a result of the radioactive decay of radium. Both radium and radon are present in the natural environment as decay products of uranium, which is present in most rocks and soils on the Earth. It is common to measure the concentration of radium and other decay progeny of uranium in terms of “picocuries per gram” (pCi/g) of soil. Radon is a gaseous isotope, meaning it is mobile in the environment. We measure the gas concentrations in units of “picocuries per liter” (pCi/l) of air.

Its important to note that radon is inert, in that it does not deliver a radiation dose to people. However, it decays with a half-life of about four days to produce seven other solid radioactive elements, which also emit radiations. A good mental picture of this is a string of firecrackers, with each firecracker representing radon or one of its decay products and each explosion representing the radiation being given off.) From a health perspective, the decay products of radon cause much larger radiation exposure than the radon itself does, since radon is an inert gas.

Let me reiterate that radon exists naturally, and there isn’t a home in the world that doesn’t have some radon in it. Outdoor concentrations will vary, depending on where one lives, from 0.1 to 0.6 pCi/L of air, which are trivial amounts. However, when radon from the ground surface is trapped inside homes, especially homes that are built for energy efficiency (i.e., few air leaks and exchanges), the concentration rises.

The average indoor radon concentration is about one (1) pCi/l of air. In some areas of the country, including Pennsylvania, the natural uranium concentration in the soil is much higher than it is elsewhere. Structures built on these types of soil tend to have a higher indoor radon concentrations because there is more radon in the soil to seep in. In extreme cases, we’ve seen indoor radon concentrations that exceed many hundreds and thousands of pCi/L.

The U. S. Environmental Protection Agency (EPA) has established an action level for radon of four (4) pCi/L for homes. (For more on the EPA’s position, please visit their web site on radon at http://www.epa.gov/radon/index.html ). This level was based on the findings of a risk assessment that assumes a hypothetical individual spends 75% of their time inside the home, with a radon concentrations that remain constant and continuous over a 70-year period. The assessment results were adjusted based upon the EPA’s level of “acceptable risk”, and the limiting concentration was derived accordingly.

However, it is important to note that making the leap from radiation dose associated with radon inhalation to lung cancer relies on this thing called the Linear No-Threshold (LNT) Hypothesis. The LNT Hypothesis states that any exposure to radiation – in this case, radiation given off by radon and its progeny – will lead to an increased chance of contracting lung cancer, regardless of how low the dose might be. In other words, the higher the indoor concentration of radon and exposure duration, the greater the theoretical effect. For more on the LNT Hypothesis, go to the Plexus-NSD web site under “Radioactivity Basics” and check out the tutorials on “Radiation Risks”, which includes “The LNT Hypothesis”.)

There are a number of considerations that makes the EPA action level for radon in homes highly conservative, meaning it over-predicts the risk. For starters, the LNT Hypothesis is the subject of some controversy in the scientific community. For example, there is no demonstrable evidence of radiation-related health effects associated with doses less than 25,000 millirem in a year, and doses in the 100,000 millirem per year range are temporary and reversible. (For more on these radiation units, go to the Plexus-NSD web site under “Radioactivity Basics” to read the tutorial on “Basic Concepts”.) Reputable scientists stand firm on the fact that there a dose threshold that must be crossed before the question of effects becomes valid. It will take a while, but once the regulatory community accepts the fact that doses within the range of natural background do not result in effects, the action levels for radon in homes will likely change.

As an aside, there are also known compounding effects that contribute to the EPA’s radon risk coefficients. Smokers who are exposed to radon tend to experience more severe adverse effects than non-smokers do. Other indoor air pollutants make the consequences of radon exposure appear worse than when they are not present. Addressing these compounding conditions can often reduce the risk far more than efforts to reduce radon concentration alone.

Finally, let’s get back to the issue of radon concentrations in homes and the fact that it isn’t constant. Concentrations tend to reach their maximum levels when air exchanges between the indoors and outdoors is minimized (e.g., in the winter and perhaps in the summer if air conditioning is used). Times of the year when windows are typically left open, such as in the spring and fall, increases air exchanges and reduces the indoor radon concentration significantly. Concentrations also tend to vary depending on where you located within your home. For example, measured levels in a basement or on a ground floor are almost always higher than they are in upper floors.

So with all of that said, I don’t agree with your observation that you are doomed to get lung cancer because of the measured radon concentrations in your parents’ basement at a single point in time. We’re guessing you did not live in their basement as you were growing up, but instead spent most of your time in above-ground floors. In addition, the radiation dose associated with the radon concentrations you reported is far to low to result in demonstrable risks, even though the LNT Hypothesis would predict otherwise.

From a medical standpoint, we always defer to recommendations of the medical community as they know patient needs a whole lot better than us physicists. However, doctors these days have many tools at their disposal that are amazingly capable of detecting diseases early, and even more tools for treatment. Routine medical monitoring that you would likely do anyway sounds like the best way to proceed. We also hope you will put away your concerns about radon and focus on the fun things in life, like gardening, bicycle riding, vacations, or whatever it is that interests you. Best wishes!

Q# 47: Hi, you have a tremendously informative website. Very impressive! I have a question I hope you can answer. My kids, 13 and 12, have been invited to travel from the United States (where we live) to play in a 10-day youth baseball tournament in Japan this coming July. We are all very excited to go, but EXTREMELY concerned about the possible health effects from the radiation accident that happened a couple years ago. My question is, do you think it’s safe to go? I don’t want to deprive my kids of the trip, but also don’t want to expose them to unnecessary health and radiation risks either. What are your thoughts? Thanks! (03/27/14)

Date: March 27, 2014

Answer: Let’s start first with a “thank you” for the kind comments on the Plexus-NSD web site. We appreciate feedback of all types, and we particularly like it when its good!

Our second order of business is to reiterate that the events that transpired in Japan as a result of the earthquake and tidal wave were definitely tragic, and Plexus-NSD’s collective hearts are still going out to the population for their loss and their struggle as they rebuild. The Fukushima nuclear power stations also took a big hit, and there was indeed a significant release of radioactivity to the environment as the Tepco workers struggled valiantly to bring things under control. They did amazing jobs under the most trying of circumstances, and life returned to normal in Japan thanks, in no small part, to their efforts.

If you’ve been reading the news lately, it seems as if everyone in the U.S. who has purchased a radiation detector at the local hobby shop is out measuring the environment for radioactivity. Well, guess what? If you look for radioactivity, you will surely find it! It truly is everywhere, so just owning a radiation detector, with no fundamental understanding of what the “clicks” or “beeps” it makes really mean, really doesn’t serve any purpose other than to alarm people unnecessarily. We recommend you look carefully at who is reporting radiation levels around the world and in Japan before taking any readings or projections based on those readings to heart.

Agencies ranging from the United Nations, the World Health Organization, Japanese regulatory agencies and even our own Nuclear Regulatory Commission have been monitoring and evaluating radiation levels in Japan almost from the moment the Fukushima emergencies were declared. The released radioactivity has been dispersing itself through the air, the ground and the water, and ambient concentrations almost everywhere throughout the country are low. A March 14, 2014 travel advisory from Japan states that the only remaining areas of concern within the country are in the immediate vicinity of the damaged reactors, with the rest perfectly safe for both residents and tourists (see http://www.japantravelinfo.com/news/news_item.php?newsid=431).

With that said, we’re pretty sure the hosts of the up-coming baseball tournament your sons will be participating in are well-aware of radiological issues within their country, and likely elected to NOT hold the tournament in the immediate vicinity of the Fukushima plants. For example, if the tournament happens to be in Tokyo or thereabouts, the radiation levels there in July won’t be much different than the levels in your home town. In fact, your sons will likely receive more radiation dose just flying to and from Japan than they will during their entire 10-day stay in the country.

What? You didn’t know that we all receive a measurable radiation dose during airplane travel? Well then, you might want to check out the tutorial section of the Plexus-NSD web page for more information on our radioactive world. In particular, check out this write-up: http://www.iem-inc.com/information/radioactivity-basics/its-everywhere.

With that, we arrive at our final order of business . . . to wish your children “bon voyage” on their up-coming trip to Japan. It will be a fantastic experience, and one that they won’t soon forget. And if their team out-scores all of the others in the tournament, so much the better. Good luck to them both!

Q# 48: We manufacturer I-125 and Co-57 calibration sources for checking Gamma Counter performance. We ship under the DOT label UN2910 for excepted quantities of radioactive materials (less than 10uC). We have been shipping internationally for 30 years but not there are requests that we provide paperwork to be supplied with the orders that we have not been asked for previously. What paperwork is required to ship internationally, specifically to India, Germany, Ireland and Canada? (01/30/14)

Date: January 30, 2014

Answer: The rules and regulations for shipping radioactive materials, both within the United States and internationally, can be a bit complicated and require a serious commitment of time in order to stay current on them and how to interpret them. However, I suspect your recent requests for paperwork are not related to changes in the shipping regulations, but rather they are in response to the way individual countries chose to license or permit the use of radioactivity. I can give you some general information, but with it comes a serious caution that it is indeed generic and may not be the right information for your circumstances.

Let’s start first with some shipping requirements. The rules for shipping radioactive materials via air transport, are different than ground. Domestically, the U. S. Department of Transportation (DOT) promulgates the rules for surface shipments in Title 49, Code of Federal Regulations (49 CFR). In 49 CFR 173.421, “Excepted packages for limited quantities of Class 7 (radioactive) materials”, we see that a package that contains limited quantities of radioactive material that does not exceed the limited quantity package limits specified in Table 4 in 173.425, are excepted from the DOT’s requirements for specification packaging, shipping papers and labeling. However, the package must be marked with the UN identification number marking requirement described in 173.422(a)), which sounds like it would be UN 2910 for your sources.

According to 49 CFR 173.425, the quantity limits for Co-57 and I-125 are 270 millicuries and 81 millicuries, respectively. However, you must also limit the total package activity such that the sum of fractions does not exceed unity. In addition, the radiation exposure rate at any point on the external surface of this package must not exceed 0.5 millrad per hour. Finally, the outside of the inner packaging or, if there is no inner packaging, the outside of the package itself must bear the word “Radioactive”.

Because the DOT rules harmonize with the International Atomic Energy Agency’s (IAEA’s) rules for international transport, a package that meets the DOT requirements will be compliant with the IAEA requirements and can be shipped internationally. However, once it arrives at the receiving country, the package must meet that country’s requirements before it can move from customs to its end destination.

Now let’s move on to permitting. Each of the countries you listed have adopted most but not necessarily all of the recommendations provided by the IAEA for the safe use of radioactivity. In the current version of their recommendation, “Radiation Protection and Safety of Radiation Sources” (IAEA Safety Standard Series GSR Part 3, Schedule III), it states that a company or agency should license or permit the use of any radioactive material that has the potential to create conditions in a public setting that exceeds one (1) millisievert (i.e., 100 millirem per year). You can read the document for yourself at (http://www-ns.iaea.org/standards/documents/general.asp?s=11&l=90 ). The IAEA does not provide details about how to complete a dose assessment, so its up to each country to figure out how to implement this IAEA recommendation.

I’m going to guess that all of the paperwork you’re being asked to provide is related to the permitting recommendations of the IAEA and not anything to do with shipping. After the port or customs office receives the package, they have a series of forms and reviews to complete before they allow it to enter the country. That means the information being requested from you could vary by country because they are each implementing the IAEA recommendations differently. However, we’re also guessing the additional information is to permit someone to assess radiation doses by having information about source terms and exposure pathways. Whatever you provide to them will help determine whether a license to possess is required or not.

As you can see, the international shipment situation has become a lot more complicated over the past few years, and you’re not the only one being hit by a flurry of new paperwork requirements. We’ve been working with a number of other companies facing the same thing you are, and while we’ve managed to get things on track to shipments can take place with out delays, these clients do have more to do, more paper to provide, and they’ve incurred additional costs than they had just a few short years ago. If we can help with the specifics of your situation, don’t hesitate to give us a call.

Q# 49: The Cs-137 specific activity listed in the table of specific activities does not appear to be correct. With a half-life of 30.08 years the SA should be closer to 88. The 98 listed may be a typo, but it should corrected

Date: January 22, 2014

Answer: As soon as we received your e-mail, we broke out our trusty calculators and did a quick check. A quick way of approximating specific activities is to determine the ratio of the Radium-226 (Ra-226) atomic number, times its half-life, divided by the product of the atomic number and half life of the isotope in question . . . Cesium-137 (Cs-137).

The atomic number of Ra-226 just happens to be 226, and its half-life is 1,602 years. If I multiply those two numbers together, and then divide them by the product of the atomic number and half-life of Cs-137 (i.e., 137 and 30 years), I get 88.09. Armed with the correct value, we edited the erroneous web page accordingly.

Thank you very much for taking the time to notify us. We’re in your debt!

Q# 50: You have a tremendous website, from both design and informational contexts! My 13 year old son’s two front (upper) teeth seem to be a MAGNET for injury! He has broken them twice, gotten them hit with a baseball a couple other times, chipped them on trampolines, etc. It keeps happening over and over. Unfortunatley the dentist is concerned these teeth have been injured so many times the roots are weakening. So she (the dentist) takes at least 2 x rays of these teeth at least every six months to monitor them and make sure the roots are still health. But my husband and I are very concerned repeated x rays in the same spot over and over (not to mention the regular bitewing and full mouth ones he routinely gets) will be too much for our son and he could get brain cancer or thyroid cancer. What is your opinion here? Should we allow the dentist to keep xraying these teeth every time? Thanks! (2/28/14)

Date: February 28, 2014

Answer: First off, thanks so much for the kudos on the web site! We appreciate feedback of any type, especially if it’s a kind word or two! Second, we’re betting that son of yours really keeps you and your husband on the go, in more ways than one! Third, let’s see if we can’t answer your excellent questions. However, before we cut to the chase, let’s lay a little groundwork first by giving you some information about medical and dental x-rays that might help you understand this issue better.

X-rays constitute one of several examples of “ionizing” radiation, that is, radiations having the ability to “ionize”, or strip off electrons from electrically-neutral atoms. Historically, the term “x-ray” originated in 1896 when one of the world’s now famous nuclear pioneers – a man by the name of Wilhelm Roentgen – discovered mysterious penetrating rays which he appropriately called “x” (i.e., unknown) rays. X-rays occur when atomic electrons outside the nucleus fall from a higher energy level to a lower one. The difference in energy is typically emitted in the form of an x-ray. We invite you to read the “Radioactivity Basics”section of our web page at http://www.iem-inc.com for additional information on this and other forms of ionizing radiation.

Diagnostic x-rays are still probably the most commonly employed form of radiology, a science that generally speaking, uses imaging techniques to allow doctors and dentists to see inside a patient’s body. However, the number of x-rays people need is determined by physicians or dentists. As you know, these professionals take ethical vows to administer only those procedures that are deemed necessary to diagnose the patient’s medical situation.

I cannot stress enough that the benefits obtained by ordering those procedures by far outweigh the radiological risks associated with them. Can you imagine what the risk would be if a dentist or doctor did not have access to or did not use these valuable diagnostic tools? Diseases and adverse dental conditions that are readily treatable when diagnosed early in their progress could escalate quickly, jeopardizing the ability to retain teeth . . . or worse. When medical or dental issues are allowed to progress too far without treatment, conventional treatment modalities are often ineffective.

Generally speaking, the amount of radiation dose received during a typical dental procedure (i.e., a few millirem at the most) or lumbar spine procedure (i.e., about 130 millirem) is trivial in light of the amount needed to result in demonstrable radiation-related health effects. There has never been a demonstrable health effect associated with radiation exposures below 10,000 millirem. And even for acute exposures between 10,000 and 50,000 millirem, the effects are typically small and reversible. It takes very high radiation exposures, a whole lot higher than those associated with annual dental exams and mammograms, for there to be any increased risk of effects (i.e., cancer) above the normal population incidence.

Now let’s take a look at where the radiation goes when a dental x-ray procedure is performed. X-ray machines in dentists’ offices are highly collimated, meaning the x-ray beam is tightly focused onto the film or imaging sensor placed into the patient’s mouth. Collimation serves two purposes; it ensures the proper amount of x-ray energy – no more, no less! – is used to produce the image, and it keeps scattered x-rays that add nothing to the quality of the picture from irradiating the patient. The same sort of thing is true for lumbar spine studies, where the primary x-ray beam is usually pointed downwards (i.e., towards the floor).

What does collimation have to do with your question? Unless someone or something is in the direct “line of sight” of the x-ray beam, that someone or something receives very little radiation exposure, if any at all. In fact, the patients themselves receive their radiation dose in the area of the film/sensor and not to the rest of their bodies. As I mentioned above, the dose at the imaging location itself is far too low to result in any sort of demonstrable health effects. (For more information on typical medical and dental x-ray exposures and how they compare to the risks of radiation-related health effects, we invite you to visit the Plexus-NSD web page under the “Tool Box” and the “Radioactivity Basics” sections.)

Now let’s talk a little bit about lead aprons, which is an issue that requires some clarification. Many years ago, dental x-ray equipment was a lot less sophisticated than it is today. Not only that, the type of film used was much slower than film or digital imaging media we use now. As a result, radiation protection professionals practicing back in the early 1950’s found that radiation doses to patients from full-mouth diagnostic exams could be substantially reduced by placing a leaded apron over the patient.

Technological improvements in equipment and film types in use today, plus the collimation we just discussed, have pretty much eliminated the need for leaded aprons. On the other hand, patients often expect to have an apron placed over them during their procedures. Therefore, most dentists would prefer to accommodate them rather than get into a discussion as to why one is not necessary (i.e., dentists even today continue to offer the use of leaded aprons to their patients simply to ease their concerns).

Of course all of this discussion presumes your son’s dentist follows all of the other rules and requirements for the safe and effective use of x-rays. Doctors and dentists who have been given a permit to operate diagnostic x-ray machines have quite a number of obligations to fulfill. They are required by law to deliver only the amount of radiation necessary to achieve their diagnostic goal. Not only that, they are supposed to have operational procedures in place to keep the number of “re-takes” to a practical minimum. There is no avoiding the occasional re-take, but regulatory agencies start sitting up and taking notice when they see unnecessarily high re-take records during their inspections of the doctors’ offices!

Here at Plexus-NSD we recommend you and all of your family members exert your rights whenever possible. Consequently, you should feel comfortable about posing the same questions you raised in this forum to your health care professionals whenever the opportunity arises. They are the only ones who know your specific course of treatment and are thus prepared to not only provide you with the answers that you seek, but to put everything into perspective in light of your specific medical condition. As with any medically-invasive procedure, you are entitled to answers to all of your questions, thus a dialogue of this nature will be helpful in easing your anxieties.

You are also within your rights to ask your dentist to “image gently” whenever the question of x-rays for your son comes up. If you have any concerns about a scheduled x-ray session for your boy, feel free to use the following in your communications with his dentist: (1) will there be a clear medical or dental benefit to my son by performing these studies? (2) Will you be using the lowest amount of radiation for adequate imaging based on the size of my son? (3) Will you only make images in necessary areas? (4) Will you do everything possible to avoid multiple (i.e., unnecessary) images? (5) Are there any alternatives to doing these x-rays in order to determine the best course of action for my son?

Above all, you should not avoid future radiology procedures for medical or dental diagnosis and treatment for anyone in your family, including your accident-prone son, simply because of a fear of radiation exposure. It would be much riskier to lose the benefit of these important diagnostic tools than to incur the trivial radiation exposures associated with them. Your health care professionals have your best interests at heart.