bend aS a . . ' . : . Bg ee dete at nn ae a Samal place after the first 1 or 2 years after deposition®’”. in 1967 the soil samples indicate most of the activity is Since still in the first inch of soil we can probably discount weathering as an important factor in lowering the exposure rates on Bikini Tsland. The levels on Nam and on some of the other larger complexes, where ®°¢o and other relatively short-lived isotopes are the mayor 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 assessirg 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, ard spectrometer results indicate we have obtained a reliable and comprehensive picture of the external gamma radiation environment om the atoll. The soil sample results, although net as consistent with the other data as could be desired due to the problems of obtaining representative samples in a very irhomogenecus distribution, do nevertheless substantiate the fieid spectrometric predictions as tc the relative importance of various emitters in the soil. The importance of the flteid spectrometric measurements in expanding and increasing the information of the survey meter readings again itilustrates the utility of such a system in undertaking an environmental radiation survey. Comparabie data on the composition of the radiation field could only have been cbhtained by analyzing hundreds of carefully obtained soil samples, if at all. The data in this report shculd form a solid basis for estimating external dose to a retyrning population as a -~ 42 - cae TR Re aRE eR gr a re tere cporeeeermetnierrpememe 7° fee eae apmebenhalt nanan San oe function of time after return, assuming with the aid of the survey team's anthropoiogist various realistic models for their living conditions, areas of habitation, and daily habits.