fallout arrival and cessation time were reported by many persons at each of these locations (Sh57, Ts55), except Utirik, and were in reasonable agreement with Dunning's values (see Table 3). On the basis of distance vs granule-size extrapolations and meteorological considerations, we also conclude that fallout would not have been visible at Utirik. On Rongerik, a set of film badges was present and exposure results were obtained (S055). Survey instrument readings and the film badge results led Sondhaus to postulate total gamma exposures, from the time fallout began up to the time of evacuation, of 0.027, 0.022, and 0.018 C kg! (106, 86, and 70 R). These values were based on three assumed fallout durations of 8, 12, and 16 hours, respectively. One film badge that remained outdoors at Rongerik gave a reading of 0.025 C kg~! (98 R). This total exposure from the time of fallout to evacuation corresponded to a fallout duration of 9.6 hours, which compares closely to the 9-hour value derived from fitting visual observations of fallout duration with distance from the detonation site (see Section II.D of this report). For whole-body dose estimates, Sondhaus appears to have assumed a 12-hour duration for all locations in order to conform to "constant fallout." The definition of “constant fallout" was not clear. Sondhaus also writes that “fallout probably would not be uniformly heavy throughout, the first portion being the most intense and the balance decreasing with time” (Cr56). 4. Rate-of-Rise of Exposure Rate. The rate at which exposure rate rises to the peak value has an effect on estimates of whole-body dose. A rate-of-rise in exposure rate at Rongerik Atoll was estimated from monitoring instrument read- ings taken for one-half hour (S055). Additional rate-of-rise information was determined from results supplied by Peterson (Pe81). Exposure-rate contours from graphs provided by Peterson were evaluated at different times at the Rongerik location. A best fit of the results yielded an exponential rise in exposure rate. A comparison of the two, measured rise versus predicted rise, indicated a wide discrepancy, the measured rise being much steeper. These results are tabulated in Table 4. It is not clear which exposure-rate measurements Peterson accepted for normalizing his results. It is clear that he accepted at least one measurement at some location because he estimated whole-body dose. If both the Peterson and the Sondhaus whole-body dose results are to converge on the results for the Rongerik exposure-rate survey, which was made 9 days post-detonation (0C68), then Sondhaus's estimate of whole-body dose would have to be greater than Peterson's estimate, not less. This is because Peterson required a much slower rate-of-rise in exposure rate than did Sondhaus. 5. Comparison of Airborne Activity Concentrations. Air activity concentrations at Rongelap and Sifo Island were computed from the meteorological re- sults provided by Peterson for 13ly and 1331 (pe81). For comparison, results for air activity concentrations of 1317 and 133: were estimated from the Bikini ash composition and are tabulated in Table 5. The cumulated activity and the airborne activity concentrations determined by either method do not agree. In summary, the Peterson-based approach towards estimating thyroid dose requires fur- ther refinement in order to achieve correspondence with all available information regarding external exposure, exposure rate and activity concentrations in air.