fishermen and lasted for 5 hours (Ts55). It was then seen at Rongelap Island at 210 km (130 miles) at 5 hours post<-detonation and it lasted for 7 hours (Sh57). Fallout reported by military personnel stationed at Eniwetak Island, 270 km (170 miles) from ground zero, was first observed at about 7 hours post-detonation (Sh57), and it lasted into the night and perhaps into the next day (Sh57). From a linear regression fit of the values for distance versus time of arrival or distance versus time of duration, we extrapolated to arrive at estimates of fallout arrival and cessation times of 17 hours and 36 hours post<detonation, respec‘tively, at Utirik Island. These derived values for fallout arrival and cessation times departed somewhat from the original estimates of Sondhaus. On the basis of Eq. (2) and the new estimates of fallout: arrival and cessation time, we determined a granule size distribution for the Utirik Island location. Based on Lavrenchik'’s summary (La56) we assumed that activity of a granule was proportional to the 3.5 power of the size, and used Eq. (2) to pro- duce an activityversus granule size distribution (see Figure 8). The relative number of granules in each size class was based on the Bikini ash distribution (Su56). The granule size corresponding to the median activity at Utirik Island was about 14.5 um (6 x 1074 in.). The granule size distribution estimated by us was in agreement with the fact that fallout was not visible to the eye at Utirik. The cumulative percent of total activity deposited on the surface of Utirik Island (see Figure 9) was also estimated. An adjustment for radioactive decay, for the period of time when fallout began to the time it reached the surface, was not accounted for by us when Figures 5, CUMULATIVE % OF ACTIVITY DEPOSITED To 1 7, and 9 were drawn. q ¢ The activity referred to in these figures q 507 | OOF E | 80 7 O20 : 20 Y 5. aoe Oo 14 wz l 167 j 193 | 22 J 247 ! 273 30 YY (Or O 0 4 poe ~ s peer? YY 8 12 — 16 20 AVERAGE PARTICLE SIZE, um Figure 8. Activity vs granule } | Uy HOURS POST BRAVO size for Utirik 4 Figure 9. Cumulative % of activity deposited on Utirik Island vs time Island fallout. ,-27- NN poss BRAVO detonation. KX Cay non 3 a és