place after the first 1 or 2 years after deposition®’”. Since in 1967 the scil samples indicate most of the activity is still in the first inch of soil we can probably discount weathering as an important factor in lowering the exposure rates on Bikini Island. The levels on Nam and on some of the other larger complexes, where *°eo and other relatively short-lived isotcpes are the major contributors, although at present in general higher on the average than Bikini Island, will decrease more rapidly and in a few ©°co halflives will probably exhibit levels generally much lower than Bikini Island. Since the scil on some of these islands contain very little organic material, weathering may result in an even more rapid decrease in exposure rates. Thus, the levels on Bikini island itself are likely to be the limiting factor in assessing the long term hazards to any future population living on the atoll and centered on Bikini Island. The consistency of the various portable detector, ionization chamber, TLD, and spectrometer results indicate we have obtained a reliable and comprehensive picture of the external gamma radiaticn environment or the atoll. The soil sample results, aithcugh nct as consistent with the other data as could be desired due to the problems of obtaining representative samples in a very inhomogenecus distribution, do nevertheless substantiate the fieid spectrometric predictions as tc the relative importance of various emitters in the soil. The importance of the fteid spectrometric measurements in expanding and increasing the information of the survey meter readings again illustrates the utility of such a system in undertaking an environmental radiation survey. Comparabie data on the compcsition of the radiation field could only have been cbhtained by analyzing hundreds of carefuily obtained soil samples, if at all. The data in this report should form a solid basis for estimating externai dose to a returning population as a function of time after return, assuming with the aid of the survey team's anthropologist various realistic models for their living conditions, areas of habitation, habits. ~ AQ = and daily