CHAPTER 2
FIELD DOSAGE DATA
2.1
EARLY DATA
When the exposures began, no monitoring personnel were in the
vicinity of any of the contaminated islands, One of the first indica
tions of a fallout was visual, when
in the air on each of the islands,
vation, although conflicting, serve
of the cloud at each island, except
a snow-like material was
The reports on the times
to establish the time of
at Rongerik (see Chapter
observed
of obserarrival
6), Here
the first evidence of a radiation field was observed when a low-level
gamma background monitoring instrument at the weather station began to
register and then went off scale at 100 mr/hr at approximately H + 7.4
hours, Table 2,1 lists the readings of this instrument during the
half hour preceding this time (Reference 2), These data are the only
information available on the initial rate of increase of gamma dose
rate on any of the islands,
At the time of evacuation of the military personnel from Rongerik
on 2 March and the Marshallese from Rongelap, Ailinginae, and Utirik
on 3 March, dose rate readings were made on each island,
This was done
with AN/PDR-39 radiation survey meters which were available at the time
and which had not been calibrated beforehand. Their operating condi-
tion was not known at the time of use, The readings of these instruments are given in Table 2.2, and constitute the earliest data on gamna
dose rates in any of the areas (Reference 3).
2.2
EXPOSURE CONDITIONS
So far as is known, the individuals exposed on Rongelap and
Ailinginae remained outdoors and had no access to shelter of any kind
on the islands, No measures were intentionally taken to protect the
skin, but clothing was worn to a degree sufficient to shield from most
of the deposited beta activity. In addition, much of the fallout skin
contamination was removed from some individuals, as a result of their
swimming and fishing in the lagoon at the time. On the other hand, the
heavy coconut oil hair dressing used by the Marshallese tended to con=
centrate radioactivity in the hair,
The surface contamination on the
ground was apparently fairly uniform over the islands, so that the calculation of average gamma doses from this source appears justified,
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