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, 10 ~ ee = see = 8 - _. 08 & a 8a - Oe ° ~_- o a = « « e008 eee 798 o