CHAPTER 2 FIELD DOSAGE DATA 2.1 EARLY DATA One of the first indica» tions of a fallout was visual, when a snow-like material was observed . The reports on the times of cae a * in the air on each of the islands. dow Bie amt baat When the exposures began, no monitoring personnel were in the vicinity of any of the contaminated islands, of the cloud at each island, except at Rongerik (see Chapter 6). 7 vation, although conflicting, serve to establish the time of arrival :°— a the first evidences of a meen field was observed when a low-level garma 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 tine (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 Marshailese from Xongelap, 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 condition was not known at the tine of use, ; - The readings of these instru- ments are given in Table 2.2, and constitute the earliest data on gamma dose rates in any of the areas (Reference 3}, 2.2 EXPOSURE CONDITIONS Se 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 worm to a degree sufficient to shield from most of the deposited beta activity, In addition, much of the fallout skin contanination was removed from some individuals, as a result of their swinming and fishing in the lagoon at the time. On the other hand, the heavy coconut oil hair dressing used by the Marshallese tended to concentrate radioactivity in the hair. The surface contanination on the ground was apparently fairly uniform over the islands, so that the cale culation of average ganma doses from this source appears justified, 5