wm ™ et oO ”N ct Q on a ct pan and regional fallout contamination of islands in the ct t central Pacific basin, uU c bea rd s oD oO oO te a acific Nuclear Testing Program resulted in as Micronesia. ern Marsnall in an area which is generically known Most eof this contamination affected the North-| Islands of eastern Micronesia, which either served as the actual test sites or which were in relatively close proximity to them. Since all of the Marshall Islands are low coral islands or atolls, the natural radioactivity content of their soil is among the lowest on earth; and their natural radiation environment is dominated by the contribution of cosIn contrast, the high islands of the Caroline groups, x mic rays. to the west or the Marshalis, are characterized by volcanic + soils having a significant complement of radionuclides in the uranium and thorium chains. Several field trips by SgEP Division personnel to Micronesia between 1975 and 1980 have afforded opportunities toa study the natural radiation environments of the coral atolls of the Marshalls and several high islands in the Carolines; and to evaluate the contributions of fallout fission and activation products to the inventories of soil radioactivity in these locations. The analytical methods employed included in situ gamma spectrometry and exposure rate measurements with pressurized ion chamber survey instruments. These measurments were supplemented by Jaboratory analyses of soil samples. The rasults of these studies have indicated that Significant contributicns from radioactive fallout can be evaluated in situ with relative ease on coral islands. In contrast, the higher natural radioactivity content of high island soils,