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 -