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 af 527 x 10 : C kg h (22 Rh o_gAt Utiyik ghe peak yas 15x10" Rh’ ~) and at Sifo 5.2 x 10 C kg”* h'~ (20 Rh’). Ckg h’ (0.59 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. 50.$—_——-- ’ at | a ne mt =a \ Y,Gx 5; wh - 1 = - 6.001 >< 0. | lil c> Sui 2 — 700005 Se J 25 250 SE 05} ; 40.008 aT By tos 10k 40.01 Sr Evacuation| c - 9 UTIRIKA, ISLAND wo 10 No ,| Bs NL»,20.00 $8 0! >< < jo.00008 LN! 100 HOURS POST DETONATION ON MARCH |, 1954 35 wi