APPENDIX D. 1. DOSIMETRY Introduction Settlers of Bikini Atoll will be exposed to both external and internal man-made sources of radiation as a result of contamination gf jot! by cesium-137, and to a lesser degree be other radionuclides Table 1). Internal exposure accounts for about 80% of the estimated radiological dose at Bikini and Eneu [Istands. Most of the internal exposure results from radionuclides ingested via consumption of terrestrial foods, particularly coconut meat and fluid. For the two principal islands, the general conclusion is that Eneu meets the Federal radiation standards but Bikini does not. In the following we discuss various parameters that affect estimated doses and compare estimated body burdens to those measured by wholebody counting. We also briefly describe the dose calculation methodology. 2. External Exposure External exposure to the gamma rays of cesium-137 was measured in a detailed terrestrial survey of Bikini and Fagu Islands in 1975 (1) and by aerial survey of the entire atoll in 1978 - Both were in good agreement (Report, Table 1); the calculated 30-year doses (1987-2016) based on them are 0.27 rem for Eneu and 3.5 rem for Bikini Island. These estimates do not include the reduction by a factor of two or so, from shielding by the house and by crushed coral which is customarily spread around the housing area, due to spending a large part of each day indoors and around the family dwelling. External exposure from boating or-swimming in the lagoon jis trivial. The beta radiation contribution to the external dose was evaluated at Enewetak Atol1(3). The median beta dose contribution to the skin (i.e. “shallow dose" in keeping with the concepts set forth in ICRU 25(4 ) and eyes, in excess of the measured external gamma dose, is about 29% at 1 meter height above the ground surface. The range of values was 16% to 50% depending on the ground cover. Thus, the dose calculated from external gamma measurements should be multiplied by 1.29 to estimate the shallow dose at Enewetak. Other than the increase in dose to the top few millimeters of skin, the rest of the wholebody and bone marrow dose would be unchanged from the external gamma estimate. The ratio of Sr to Cs in the soil is considerably higher at Enewetak then at Bikini. Thus, the contribution of beta radiation in excess of the measured external gamma dose would be less at Bikini than at Enewetak. Based on measurements made at Enewetak and the relative ratios of Sr to Cs in the top 5cm of soil at the two atolls, the total external exposure at Bikini at 1 meter due to external gamma plus beta radiation would be about 15% greater than the external gamma measurement. The total unattenuated external exposure dose to the skin (i.e. shallow dose) at the ground surface could be 50 to 100% greater than the external gamma dose at 1 meter. The external gamma dose listed in reference 3 and this report are based on open field external gamma measurements. They do not include reductions which can be as much as a factor of 2 or more which occur as a result of the considerable time spent in and around the houses from shielding due to rhe houses and crushed coral which is customarily spread around the houses! The reductions in the beta dose could be even greater because clothing, shoes, sandals and Pandanus mats on which people commonly sit or lie would absorb most of the beta radiation and people only spend part. of their time with the wholebody on the ground surface level. I00010b D-1