SLIDE 33 External exposure rate. Rate of rise in exposure rate at Rongerik Atoll was measured by a monitoring instrument for one~half hour. A best fit of the results yielded an exponential rate of rise in exposure rate. The exposure rate peaked within an hour after the arrival of fallout at Rongelap and Sifo Islands. Arrival time and peak exposure rate were estimated by us based on granule size considerations and the rate of activity deposition. The estimate of rate of rise was in agreement with the rate of rise observed at Rongerik. The exposure rate peaked within 3 hours at Utirik. Decline of exposure rate was based on the decay of 142 nuclides which precursed the Bikini Ash. The exposure rate histories at Rongelap, Utirik and Sifo Islands were normalized to the results of the radsafe survey teams of the USS PHILIP and USS RENSHAW (ocgs). The mean exposure rate at Rongelap was estimated to, peak at 5.7 x 107) C kg) bh” Rh (22 Rh). _,At Utipik the peak yas 1.5 x 10% C kg Wh! (0.59 “) and at Sifo 5.2 x 107 C kg * h~ (20 Rh“). After the cessation of fallout the exposure rate ratio between Rongelap and Sifo Islands was 3.0 to 1.0 and between Rongelap and Utirik Islands, 9.5 to 1.0. Ss -. == r n . a i 0. = we 5 oe r =z “Jo. 4 . | Ge, 10.008 J Evacuation] . | =0.001 25 ww 1b 25: S2 051 >< eT wT, » UTIRIK(A\, ISLAND . == 700008 = & “” wo 5> NN og », 30.0001 >< < 0.00005 ont oto 10 lOO HOURS POST DETONATION ON MARCH |, 1954 35 © 3S us