Determining radiation exposures for people requires quite a bit of knowledge about the person in question. Because some of this information can be difficult to obtain, a conventional approach to dose assessment is to assume that the individual has the characteristics of a “Reference Individual”. Consequently, most of the doses that are assessed for determining compliance with regulatory dose limits are really doses to a hypothetical individual with certain average characteristics. The basis for this assumption is that when the doses are low, individual differences between people, which can vary considerably, can be ignored. (The same is not true for radiation doses that approach or exceed regulatory dose limits. In this case, a person-specific assessment of dose is prudent.)
The International Commission on Radiological Protection (ICRP), in Publication 23 (1975) has defined a series of reference values that may be used for internal and external dose assessments. These values , considered to be typical of occupational workers in general, have been divided into separate sections.