Results of Gamma-Ray Exposure Rate Measurements vertical coordinate is a measure of The geographical variability of the gamma~ray exposure rates for the gamma exposure rate. Bikini and Eneu Islands is shown in elevated irregularly shaped areas Figs. 4 and 5. appear as "peaks" while the lesser The contribution due Thus, to cosmic radiation has been sub- values near the shores appear as tracted. relatively low flat areas. On Bikini Island the individual measurements from which the Note especially the low flat area the contour levels were derived are situated on the ocean side near the listed in the Appendix. center of the island Note the complex patterns displayed throughout the island. (Fig. 6a). The gamma exposure rates measured on Eneu Island (Fig. 5) show This complexity may be due, in part, to the inhomogeneity that the island is characterized by in the original fallout pattern low (less than 10 yR/h) and more or produced by the Bravo event, less uniformly distributed gamma but it certainly reflects the extensive radiation levels over the entire earth moving activities performed island. over the entire island as part of These total gamma-ray exposure the agricultural rehabilitation rates are the basis for the external program. dose estimation. The exposure rates near However, to deter- the shores are typically of the mine the annual dose and dose order of 10 to 20 yR/h, while the commitment, elevated interior values vary over a to determine the fractional contri- wide range of roughly 30 to 100 uR/h. bution made by the predominant The interior portions of the island gamma-emitting radionuclides distri- may be visualized as having a general buted in the soil. background of about 30 to 40 UR/h with experience at Enewetak Atoll and numerous irregularly shaped areas the data of Bennett and Beck? exhibiting elevated levels superim- obtained during the 1967 Bikini posed in a random fashion over Survey, we expected that general background. this it was also necessary Based on our the primary contribution to the gamma This may also be visualized by viewing the three exposure rates would be due dimensional computer generated 13766 and 600, activities in the graphical displays of soil. the exposure rates (Figs. 6a, b and c). The poser Cae erent cr soe Rees an7 a ‘Trace quantities of other gamma emitters such as -7-8~ to 1254, ,