by a factor e.
We estimate that this translates into a 15% underestimate of the
activity present if one assumes that the exposure rate was due to a smooth flat
plane of activity rather than one distributed depthwise.
Since we normalized activity intake to urine activity
excreted, the effect of this underestimate of activity per unit area was inconsequential on thyroid dose estimates. It would, of course, impact on the relative
amounts entering the body through the ingestion versus inhalation versus skin absorption pathways but not the total amount taken in. Since in our assessment
the ingestion pathway dominated, the impact on thyroid-absorbed dose would be
negligible.
vii.
Integrated Exposure and Whole-Body Absorbed Dose.
The total
integrated exposure from the onset of fallout to evacuation was 7.2 x 1072 ¢
kg“
(280 R) 1 m.above the surface of Rongelap Island.
In order to make this es-
timate, we accounted for the buildup of fallout on the ground as previously
described and accounted for the photons emitted from all nuclides Listed in
Table 13. A plot of the integrated exposure versus time was given as Figure ll.
From the decay exponents derived from Bikini ash decay and the exposure-rate survey results obtained by the radsafe teams of the USS RENSHAW and the USS PHILIP,
exposure rates versus time post-detonation were plotted (Figure 10) and
integrated (Figure 11) for Sifo and Utirik Islands. The total integrated exposure at 1 m above the surface of Sifo Island was 4.4 x 1072 c kg! (170 R) and
at Utirik Island 4.1 x 1072 C kg! (16 R). These exposures were for the period
of time from the onset of fallout to evacuation, March 1-3, 1954.
Although our air exposure estimates at early times postdetonation differ from those of Cronkite et al. (Cr56), they are in agreement
with Cronkite's whole~body and external thyroid absorbed-dose estimates... The
Marshallese reported no significant deviation from routine living patterns (see
interviews recorded by Sharp, Sh57). In a previous document by Greenhouse and .
Miltenberger (Gr77), it was shown that external exposure inhomogeneities due to
various living patterns (such as fishing in the lagoon, standing on the beach,
etc.) could be accounted for by multiplying the mean exposure rate for the island at 1 m above the surface by a factor of 0.73 to obtain whole-body absorbeddose rate. They included in this multiplicative factor a correction for the
electron density difference between air and tissue. We used another
multiplicative factor of 0.95 to convert exposure to whole-body dose. We used
this additional factor to account for attenuation and buildup of the photon flux
as it traversed the body. The energy spectra we assumed was the one given by
Borg (Bo56) for BRAVO fallout at 4 days. Thus, we estimate the external
whole-body dose at Rongelap to have been 1.9 gray (190 rad). This compares to
1.75 gray (175 rad) which was estimated by Cronkite et al.
2.
Radioactivity in Food, Water Supplies, and Air
a.
Activity in Cistern Water.
The main water supplies at Rongelap,
eight cisterns, were reported to each contain 0.23 m of water during the later
part of March and early April 1954 (Sh57). Water was drawn from six of these
cisterns at Rongelap for gross beta analysis on March 2, 1954 (see report of the
tadsafe team USS PHILIP, 0C68), and one other cistern was reported empty.
Each
tyr
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