- Results of Gamma-Ray Exposure Rate Measurements \ The geographical variability of vertical coordinate is a measure 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, the to cosmic radiation has been sub- values near the shores appear as tracted. relatively low flat areas. On Bikini Island the Note individual measurements from which 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 (Fig. 6a).. Note the complex patterns displayed throughout the island. The gamma exposure rates This complexity may be measured on Eneu Island (Fig. 5) show due, in part, to the inhomogeneity that the island is characterized by in the original fallout pattern low (less than 10 —uR/h) and more or produced by the Bravo event, but it less uniformly distributed gamma certainly reflects the extensive radiation levels over the entire earth moving activities performed island. These total gamma-ray exposure over the entire island as part of 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 uR/h, while the commitment, it was also necessary 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 this Survey, we expected that the general background. primary contribution to the gamma This may also be visualized by viewing the three dimensional computer generated Based on our exposure rates would be due to .137 Cs and 60 Co activities in the graphical displays of the exposure soil. rates (Figs. 6a, b and c). gamma emitters such as The -~7-8- Trace quantities of other 125 Sb