These distributions were in turn used to determine the rate at which exposure rate and activity increased at these island locations. Information regarding granule fall time as a function of granule diameter was derived from deposition models reviewed by Norment (No66). Four models of fallout settling were presented as a function of granule diameter and initial height (No66). Expressions for granule fall time from various heights were derived by using the model results of Davies, Hedman, Hastings or Ksanda as presented by Norment (No66). The resulting granule fall time versus granule di- ameter equation was in each case best described by a power function. Tsuzuki (Ts55), in his article, indicated the observed fallout arrival time, cessation™ time and granule size for Bikini Ash. This data was used to model a power func- tion relationship which related granule diameter to granule fall time specifi-~ cally for BRAVO fallout as follows: T= 79,5 p0-524 (2) where T = granule fall time in hours post BRAVO, D = granule diameter in micrometers. It was assumed that the largest granules in the Bikini Ash fell upon arrival and the smallest granules fell upon cessation of fallout. Equation 2 was used with the activity versus granule diameter distribution to describe the rate at which activity increased at Rongelap, Utirik and Sifo Islands and on the 5th Lucky Dragon. Equation 2 was a simple model to describe fallout arrival time versus granule diameter. The bulk of the activity of BRAVO was at the base of the cloud at 17 to 29 km above ground ten minutes after the burst (0C68). 10 Granules