a6 ‘ ‘ : - of . - . - Le . . a . . . . . . “DURATION ANDTIME DISTRIBUTION OF DOSES. 6.1 AVAILABLE DATA In Chapter 2, the only existing field data on dose rates and to- tal dose are summarized, The information does not provide answers to two important questions: (1) what was the time for each island at which the fallout cloud arrived; i.e., when did the radiation level on each of the islands rise above the nornal background and (2) how steep- ly and for how long did the radiation-level rise before it reached its maximum value and decayed away at the rate determined by its own com- position (discussed in Chapter 3); i.e., how heavy was the fallout at any time it was occurring and how long did it last? Since only the times of evacuation were directly known, assumptions on both these questions were basic to an estimate of total dose, It would have been desirable to have had an instrument on at - least one of the islands capable of recording enough data to answer these questions, ds it is, it was fortunate that there was even a low- level monitoring instrument in operation on Rongerik (Table 2.1), although its full scale capacity was soon exceeded by the rapidly increasing dose rate of the fallout, The time at which the fallout began was at least quite definitely established on Rongerik and it coincided with the time at which the snow-like material was first seen, , For the other islands, therefore, the times at which similar material had been seen to commence falling could be taken as the beginning of the radiation exposure times, It only remained to determine what these times had been, Questioning the inhabitants of the other islands resulted in a group of estimates of arrival time which were in fairly good agreement, though the manner of questioning sanetimes appeared to influence the i enantio.nail ie answers, However the times estimated in this fashion were quite close te those resulting from other information; i.e., the wind velocities at the time, the time of beginning fallout on Rongerik, and the relative distances of the other islands from Bikini. Only on Utirik was no actual observation of the fallout made; the estimate of arrival time there was made using only the time of arrival on hongerik and the windeand-distance-factors, The values of fallout and evacuation tines used are summarized in Table 6.1, . oe oe / oo ers oe “30 oe ooe ee e 20 vA Gia ~ _ © ons ee = ae & ote oe 8 8 60 ee le 4 O24 ° Jf