tor of 3. However, the population distributions illustrated a maximum factor of 5 times th: mean activity ingestion rate value. Dose equivalent rates post return were determined for members from both atolls. For Rongelap Atoll, the residents received approximately 100-200 mRem per year during the first 5000 days post return from internal emitters. principle contributing nuclide was 13765, For Utirik Atoll, the residents received ]0-15 Rem per year during the first 400 days post return. contributing nuclides were 6525 and 6066, The 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 sub-groups and for individuals was determined. row, Table 6 summarizes the results for the total body, thyroid, red mar- testes, ovaries, lower large intestine wall and the liver. The catenary compartment model of Bernard and Hayes (Ber70) was used to determine doses to various segments of the gastrointestinal tract. significantly more radiation dose from 6520, The Utirikese received 600, and 55H than did the Rongalapese due to the short mean residence times of these nuclides in the envi- ronment. 705, doses to the Rongalapese were 2.5 time greater and 1370, doses 1.5 times greater than doses received by persons at Utirik. This occured even though Utirik residents returned to their atoll 3 years earlier and it reflects the degree to which Utirik was less contaminated than Rongelap. 26