Doses from external irradiation @ A. BouviLte er AL. 149 Lagoon Relative exposure rate MB 0.58 1.0 HW 035-058 || 0.19 - 0.35 [| 0.09 - 0.19 || 0.03 - 0.09 <0.03 0 100 200 300 400 500 Ltt meters Fig. 4. Relative exposure rates (arbitrary units) across Eniwetak Island, Rongerik Atoll, in 1978. Data derived from the U.S. Department of Energy-sponsored aerial radiological survey of the Marshall Islands (Tipton and Miebaum 1981). organ dose is thus about 8.75 x 10° (Gy R') X 0.75 of 23 atolls and islands, and of three population groups While the dose conversion factor for an actual person depends onthe age and sex of the person, or, more precisely, her or his anthropometric characteristics, doses in this study were estimated for representative persons, defined as hypothetical individuals with anthropometric characteristics that are typical of those of the people who lived in the Marshall Islands in the 1950’s. Calculations using anthropomorphic phantoms of different ages (Jacob et al. 1990) indicate that body size, which is generally correlated with age, results in slightly higher doses for younger ages. Based on those calculations, we adjusted our estimated doses for representative adults to doses for younger (<3 y, including in utero) and older (3 through 14 y) children by multiplying the adult doses by 1.3 and 1.2, respectively. al. 2010a). With the exception of the populations of the atolls that were evacuated following the test Bravo of 1954 or were relocated before the testing began (see (Gy Gy') = 6.6 X 10° (Gy R‘!) for adults. RESULTS AND DISCUSSION Doses from external irradiation were estimated for the entire population of the Marshall Islands and for each of the 20 tests that took place at Bikini or Enewetak that resulted in measurable fallout on inhabited atolls of the Marshall Islands (see Table | in Simonet al. 2010a). The population of the Marshall Islands wasclassified into 26 population groups consisting of the permanent residents that were evacuated or relocated (see Table 2 in Simon et Simon et al. 2010a, Table 3), we have assumed that our estimated doses pertained to representative persons from each atoll, and that there was no movement of those people from one atoll to another. Estimated exposures As shown in Fig. 1, the ground-level exposure rate decreases very rapidly with time after detonation, by a factor of more than 1,000 during the first 1,000 h (about 40 d). For that reason, the lifetime exposure varies substantially with the fallout TOA, as was shown in Table 2. The example TOA values that were chosen for Table 2, with the exception of the extreme value of TOA = 0, correspond to the range of values estimated for the inhabited atolls after the various tests (Becket al. 2010). As previously indicated, most of the external exposure occurs within the first year following the detonation. The influence of the weathering effect is barely noticeable during the first month after the detonation and only plays a substantial role after one year. It is, however, extremely important to take the weathering