Le i Be eee ee eee ee we ha i ek tle not considered, since fallout activity in the air would have ceased substantially by those times. . At Sifo Island, most of the fallout fell in one midmorning hour be~ tween breakfast and lunch times. Assuming the same food preparation area as at Rongelap Island, but no deposition on plates while eating, values for intake were estimated. We assumed that 60 mg of BRAVO dust was ingested at 5.5 hours post-detonation. These dust particles would have been large, 320 micrometers av- erage size, and visible on food prepamation surfaces. e. Activity Concentrations in Air. Mean air concentration estimates of activity of selected nuclides were based on fallout deposition rates. The percent of activity deposited per minute at various times at Rongelap Island was estimated by us from Eq. (2). Fail velocity corresponding to granule size was taken from Figure 8 of Holland's report (Ho63). We used an estimate of fall velocity because we did not know the height of the column of fallout over each island. Air activity concentrations at various times were assumed by us to be 1) directly proportional to the fraction of total activity deposited per minute, 2) directly proportional to the total activity on the ground at the end of fallout (decay corrected back to various points in time), and 3) inversely proportional to fal! velocity of granules. We applied these same assumptions to surface activity results for Sifo and Utirik Islands as well. Our values for air concentration at all three islands and times post-BRAVO detonation are tabulated in Table 18. The cumulated air activity concentrations for Rongelap Island which we derived from Bikini ash were about one third the cumulated air activity concentration results of Peterson (Pe81). The air activity concentrations for Utirik Island relative to those at Rongelap Island might be expected to be less because of the exposurerate differences that were observed and because of greater dispersion of the fallout cloud. The fall velocity of a granule corresponding to the activity median size was greater by a factor of 95 at Rongelap Island than at Utirik Island, while the exposure rate after deposition differed by only a factor of 9.5. If one hypothesizes that the deposition intervals at both islands were the same, and the air activity concentrations were equal, then 95 times less exposure rate at Utirik [sland would be anticipated, not 9.5. The fallout cloud duration at Utirik was 2 to 3 times longer than at Rongelap based on granule size considerations. However, it was not long enough to account for the measured exposure~ rate results. Therefore, the air concentration at Utirik Island mest have been greater than at Rongelap (see 131y, Table 18). Given that fallout was not visible and exposure-rate measurements were accurate, longer fallout duration and higher air concentrations at Utirik relative to Rongelap were likely. The total fallout activity on the surface of Rongelap Island was still ten times greater than at Utirik Island, largely as a result of the greater rate at which granules fell to the surface of Rongelap. f. Activity Intake By Inhalation. Airborne activity intakes were dependent upon breathing rate of individuals during fallout cloud passage. We assumed breathing rate to be proportional to body mass as derived from reference mo ye fos 1 wehbe kr 4 co + - eesectinete = -~ 52 -