SLIDE 16 Granule fall time. Information regarding granule fall time as a function of granule size was derived from the deposition models which were reviewed by Norment (No66). Four models of fallout settling were presented as a function of granule size 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 complexity of each model varied, however, each investigator accounted for the aerodynamic properties of irregularly shaped fallout granules. The granule fall time result versus granule size was best described by a power function in each case. Tsuzuki indicated the observed fallout arrival time, granule size distribution for Bikini Ash (Ts55). cessation time and This data was used to model a power function relationship which related granule size to granule fall time specifically for BRAVO fallout as follows: where T = 79.5 p09524 T = granule fall time in hours post BRAVO, D = granule size in micrometers. It was assumed that the largest granules in the Bikini Ash fell upon arrival and smallest granules fell upon cessation of fallout. The times of arrival and cessation of fallout were observed at Rongelap and Sifo Islands and at Rongerik Atoll. The above equation was used to estimate granule size at these locations. The times of arrival and cessation at Utirik were based on linear extrapolation of known arrival and cessation times versus distance from detonation site. Thus, granule size at Utirik could be estimated using the ahove equation. BRAVO FALL TIME Fall Time of Size At Median Activity Location Hours 5th Lucky Dragon Rongelap Island — 3.5 5.7 Sifo Island 3.5 Utirik Island 12 21