oe - 3 - . . . os ot “-" BALLOUT CHARACTERISTICS eo | - 3.1 EXPERIMENTAL DATA In order to calculate a total gamma dose received by an individual in an area where dose rate was measured at a given time, a value for the rate of change of radiation intensity during the exposure period must be assumed, The latter quantity has often been approxi- mated using the well known Way-Wimer (t7l. ) decay law. In this case however, it was known that large amounts of Npe39 and NpehO were to be expected in the fallout of the 1 March shot, making its early decay , characteristics as well as its energy spectrum somewhat different fron those of previous detonations. It was therefore decided, that the walue of decay rate assuned to exist during the exposures should be based, as far as possible, upon experimental data fram this test. Unfortunately, no decay rates were followed closely in any of the immediate areas where the exposures occurred, and it is known that the radiochenical canposition and decay rate of the fission product mixture usually vary both with place and time, However, early decay rates in the Bikini lagoon itself had been measured in a serias of fallout samples taken at other points nearer the site of the detonation (Reference 5), Since these values were the best data available, they were used in the calculations and were assumed to hold for the fallou on each of the islands, 7 The early samples showed a consistent pattern among various loca~ tions and a decay exponent (n) of between 0,8 and 0.9 in Equation 3.1. kag(t/y2 wheres 4 = activity (d/m) at time t. . Ga) . oe . This decay exponent (n) was found experinentally to fit the data ‘for the period H+ 5S to H +50 hours, in Reference 5, The observed values are given ,