C The chips were annealed on the atoll immediately prior to being placed on the islands for the roughly three-month exposure period which ends during September 1975. At that time, the chips will be retrieved for readout at LLL. Calibration and signal fading studies are being carried out by exposing separate sets of chips to a 1376. point source before and after the exposure period. The results of the TLD measurements will appear in a later report on this survey. Results The geographical variability of the gamma exposure rates for Bikini and Eneu Islands are shown in Figs. 2 and 3. These data, expressed in units of microroentgens per hour (uR/hr}, have been normalized to the output from the pressurized ion chamber. Note that the levels for Bikini Island are considerably higher than those for Eneu Island. Also note the complex patterns displayed on Bikini Island. This complexity may possibly be due to the inhomogeneity in the original fallout pattern produced by the Bravo event as well as the extensive earth-moving activities performed over the entire island as part of the agricultural rehabilitation program. The exposure rates near the shores are typically of the order of 10-20 uR/hr, while the elevated interior values vary over a wide range of roughly 30-100 uR/hr. The interior portions of the island may be visualized as having a general background of about 30-40 UR/hr with numerous irregularly shaped areas exhibiting elevated levels superimposed in a random fashion over this general background. Eneu Island, on the other hand, is characterized by low (less than 10 uR/hr) and more or less uniformly distributed gamma radiation levels over the entire island. These exposure rates are expected to be accurate to within approximately 10%, although final confirmation of this must wait until the results of the TLD program become available. No corrections © have been made for the natural background contribution. Based upon our experience at Enewetak Atoll} and the data of Bennett and Beck? collected during the 1967 Bikini survey, we expect the primary contribution to the gamma exposure rates to be due to 13705 and 60 activities in the soil. Trace quantities of 125cy ISSE and 24] other gamma emitters such as Am are expected to contribute at most a few percent to the total exposure rates. The gamma spectral analyses of the several hundred soil samples collected on both islands will reveal the current mix of these radionuclides. ee ermeee ne ntno eee External Dose Estimation In addition to the gamma-ray exposure rates, one needs to consider the expected living patterns of the future inhabitants in order to evaluate the external dose problem. Of course, many uncertainties are inherent in the prediction of future living patterns. However, the following cases, shown in Table 1, have been proposed as a reasonable selection of possible conditions that would cover the range of doses that could be received by any sizable segment of the population.» ~4- This will allow any other reasonable “a