EVENT AND DESCRIPTION OF EXPOSED GROUPS a. The estimated durations of fallout which result from the above extrapolation of initial fallout rate for Group I and III appear too long to have occurred at the distances of these people from the shot island, since the wind velocity in the area was high enough to move the cloud over the islands in a considerably shorter time, as little as onehalf of the above indicated time. b. The accounts of the visibility of the fallouts, although conflicting, do not indicate such late cessation. c. Doses calculated on a long fallout constant rate of increase hypothesis are lower than those due to a short fallout, since a short fallout quickly deposits a large amount of activity. For both a 16 hour and 8 hour fallout assumption, a dose value was estimated. The ranges are then as follows: Table 1.2 7 d. For Utirik atoll Group IV, only a fallout time of about 12 hours orless is consistent with the later dose rates observed, provided the fallout actually began as late as was estimated from wind and distance factors. e. A long fallout probably would not be uniformly heavy throughout, the first portion being the most intense and the balance decreasing with time. The total phenomenon would thus tend toward the effect of a shorter fallout. This is supported by monitor data from other nuclear events, where initially heavy fallout is reported to produce a peak of air-borne radioactivity soon after arrival, with the airborne activity level then decreasing. The latter part of the fallout, though still detectable as dust, may then produce only a small fraction of the total dose from material on the ground. Hence the total dose may be estimated fairly accurately by assuming a constant fallout to have been complete in a muchshorter “effective” time. On Rongerik (Group ITI) a set of film badge readings were obtained which constitute the only direct evidence of total dose. Several badges worn both outdoors and inside lightly constructed buildings on the island read about 50 to 65 r, and one badge which remained outdoors over the 28.5 hour period read 98 r. Another group of badges, kept indoors inside a steel refrigerator, read 38 r. These dose values represent a variety of conditions, but, considering the shielding The dose values given in Table 1.1, based on film badge, meter and monitor data, are consistent with a constant fallout hypothesis of about 12 hours effective time.* One exception is made; the dose values for Group ITT are about 75 percent of the 12 hour fallout value, averaged for 28.5 and 34 hour exposures. This was felt to express most accurately the average air dose received by personnel who spent roughly half their time inside structures where the dose rate was later found to be roughly half that outdoors. On the otherislands such shielding was not available. Figure 1.8, illustrates the cumulation of radiation dose as a function of time after detonation. The dose rate varied continuously. The major portion of radiation was received at the higher dose rate prevailing in the early portion of the exposure period. By the timethat the assumption that the dose outside during the first 28.5 hours after the beginning of the fallout corresponded to about 12 hours of constant fallout. *Using 12 hours actually results in values which are higher than those of Table 1.1 by 3 to 11 r, Table 1.1 listing the values calculated before ali spectrum data was available, Uncertainty in all the information is greater than this difference, which is neglected. Location FArLoUTTIME i6hr Shr Rongelap (Group I)_-._._| Ailinginae (Group IT) __.. 159 r 727 209 r 92 r Rongerik (Group JII)___. Utirik (Group IV)___._-- 70r i2r 106 r l5r and attenuation factors, are consistent with iu U