year period. The standard deviation was in general 30% of the mean value for all age and sex subgroup distributions. the fact that and 137 65 This less pronounced variation may be due to . . Zn measurements took place over a 3 year interval while . . 90 Sr : Cs occurred over a 23 year interval and thus was contained in a more homogeneous population than were the longer lived nuclides. Figures 22 and 23a and 23b summarize the 906, dose equivalent results foi individuals at Rongelap. In this analysis, only the ingestion pathway was considered important. Some radioactivity would enter the body via the resuspension and direct inhalation pathways. It is known that for a given soil concentration of the stable naturally occurring analogs to the radionuclides considered here, the ratios of food and fluid intake to blood relative to airborne intake to blood, are as follows: Co > 3000 Zn > 130 Fe > 550 Sr > 10,000 Cs > 400 Thus, dietary intake of radioactive material is the principal pathway leading to internal deposition. This applies to most nuclides in the environment, however, there are notable exceptions including I, U, and Pu. External Exposure A value of .73 rads in tissue of interest per rontgen, measured in air at one meter above the surface, was used to convert exposure in air to absorbed dose in tissue. The source was assumed to be an exponential distribution of 1376. acu tivity with depth in soil, typical of aged fallout (Be70). Because of the multidirectional nature of the source, variation of absorbed dose with depth of organ was minimal. Additionally, external doses were adjusted for living pat- 43