detonation site, thus these persons would have received fallout with similar gra-
nule diameters as that given in Fig. 1 for Bikini Ash.
Their location was fur-
ther south than the location reported for the 5th Lucky Dragon (Ts57) thus less
debris fell on Sifo Island.
The fallout encountered by these people was
estimated to be off the centerline of the BRAVO cloud by about 30 kn.
4,
A Simple Model for Exposure Rate History at Rongelap, Sifo and
The exposure rate survey by the crew members of the USS PHILIP
(0C68), the early fallout decay exponents indicated by Miller (0C68) and the
time of arrival of fallout on the surface of Rongelap were combined to estimate
the exposure rate history at Rongelap Island prior to evacuation (see Table 3)
(Cr56).
This exposure rate history would not include the contribution from
non-fission fragment nuclides since it was based on fission product decay expo-
nent given by Miller (0C68).
The total integrated exposure at Rongelap Island
from the onset of fallout until evacuation was 180 R for one meter above the surface.
The maximum exposure rate of about 12 R not was estimated to occur about
5 hours post detonation, however, it was assumed that all the fallout was on the
ground at this time, that is, an instantaneous rise in exposure rate.
of the U.S.S.
The crew
PHILIP also surveyed Sifo Island and the crew of the USS RENSHAW
surveyed Utirik Island during their evacuation efforts (0C68).
The exposure
rate histories for Utirik Island and Sifo Island were given in Table 3.
In sum-
mary, the exposure rates in Table 3 were based on Miller's decay estimates and
do not account for build-up of exposure rate but are in agreement with initial
estimates.
A more refined estimate of external exposure rate history was based
on Bikini Ash as follows.
\s
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