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 Ucirik. 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 COCg8). The mean exposure rate at Rongelap was estimated to, peak af 521 x 10°? € kg bh” (22 Rh“). At Utirik phe peak yas 1.5 x 10° C kg h~ (0.59 Rh!) 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. o o O : %r i " 5 = Oe ao> 419.005 Fo Evacuation | =a: Sw S: Q Se 25 | % ew {0aS ft Of S2 0505 UTIRIK ] ae ; =7 i0.001 2° S 4; lu & i _ 30000 8 BE KON \y i | | ONL oc ae 2S of 23 0.00005 Liou 10 . {2 100 HOURS POST DETONATION ON MARCH |, 1954 35