Dependence on age at intake of committed dose equivalents from radionuclides

The dependence of committed dose equivalents on age at intake is needed to assess the significance of exposures of young persons among the general public resulting from inhaled or ingested radionuclides. The committed dose equivalents, which are evaluated using ICRP principles, depend on the body dimensions of the young person at the time of intake of a radionuclide and on subsequent body growth. Representation of growth by a series of exponential segments facilitates the derivation of general expressions for the age dependence of committed dose equivalents if metabolic models do not change with age. The additional assumption that intakes of radionuclides in air or food are proportional to a person's energy expenditure (which implies age-independent dietary composition) enables the demonstration that the age of the most highly exposed 'critical groups' of the general public from these radionuclides is either about 1 year or 17 years. With the above assumptions the exposure of the critical group is less than three times the exposure of adult members of the general public. Approximate values of committed dose equivalents which avoid both underestimation and excessive overestimation are shown to be obtainable by simplified procedures. Modified procedures are suggested for use if metabolic models change with age.