years of age ingested more activity each day than did adolescents and persons greater than 40 years of age. Maximum deviation from the average value of the daily activity ingestion rate for members of an age subgroup was no greater than a factor of 3. However, the population distributions illustrated a maximum fac- tor of 5 times the mean activity ingestion rate value. Dose equivalent rates post return were determined for members from both atolls. For Rongelap Atoll, the residents received approximately 100 to 200 mRem per year during the first 5000 days post return from internal emitters. The principal contributing nuclide was 137 C8, For Utirik Atoll, the residents received up to 15 Rem per year during the first 400 days post return. contributing nuclides were Oren and 6000. The major Dose equivalent rates to the Utirikese from internal emitters fell below 500 mRem per year at approximately 1200 days post return. The dose equivalent for population subgroups and for individuals was determined. Table 6 summarizes the results for the total body, thyroid, red marrow, testes, ovaries, lower large intestine wall, and liver. The catenary compart- ment model of Bernard and Hayes (Ber70) was used to determine doses to various segments of the gastrointestinal tract. The Utirikese received significantly more radiation dose from 6570, 6064, and 95 re than did the Rongelapese because of short mean residence times of these nuclides in the environment. 90... doses . 137 . to the Rongelapese were 2.5 time greater and Cs doses 1.5 times greater than doses received by persons at Utirik. This occurred even though Utirik residents returned to their atoll 3 years earlier and somewhat reflects the degree to which Utirik was less contaminated than Rongelap. 51