and Utirik indicated that radioactive fall-out may have been transported to otherislands. An instrument reading on Utirik (classified as non-exposed) was 0.01 Gy/hr (1 rad/hr) one hourafter detonation. Furthermore,a statistically significant increase in the incidence of thyroid tumors over background rates was observed in residents of atolls thought to be non-exposed (33). Collectively, these findings suggest that the geographic area Tepresenting the “exposed” population may have been much broader thanoriginally thought, and therefore, the exposed population may be muchlargerthaninitially reported. In addition, some inhabitants of nearby atolls chosen as part of the "non-exposed" group may have received cumulative radiation doses similar to, or even higher than, those exposed on Utirik (33). Radiation Dose Estimates The estimates of radiation dose calculated by various groups are discussed with respect to these three sources of radiation to which the Marshallese were exposed. 4.4.1. External Whole-Body Doses from the Plume Current knowledge and practice indicates that two approaches may be taken to estimate the residents’ externa! whole-body doses from sources in the passing plumeoffall-out materials. One wouid be a theoretical approach, in which the known device yield and characteristics are used to calculate a source term, and other plumetransport and radiation production; attenuation and scattering models are used to estimate typical absorbed doses near ground. Another approach would be to use observed survey meter readings, integrating dosimeter readings, etc, at the various locations over time to estimate residents’ absorbed doses. The early attempts to characterize the external whole-body radiation doses used recorded survey meter and dosimeter readings. These initial estimates are shown in Table 1. The Rongeiap inhabitants were thought to have received the highest doses, because of their proximity to the blast and the approximately two-day delay before evacuation. Although Ailingnae is physically closer to Bikini than either Rongelap or Utirik (see Figure 1),it is & Ph P23 ae i9 ce 4.4