eee ne 2 EVENT AND eB. DESCRIPTION The estimated durations of fallout which result from the above extrapolation of initial fallout rate for Group I and Iil 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 httle as one-- half of the above indicated time. OF ENPOSED Theaccounts of the visibility of the fallouls, Doses calculated on a long fallout constant rate of increase hvpothesis 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, no dose value was estimated. The ranges are then as follows: f d. For Utirik atoll Group IV, onty a fallout time of about 12 hours or less 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 umiformly heavy throughout, the first portion being the most intense and the balance de- creasing with Gime. although conflicting, do net indiente such late cessation. — GROUPS The total phenomenon _ would thus tend toward shorter fallout. the effect of a This is supported by moni- tor data from other nuclear events, where intially 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 much shorter “effective’’ time. Table 1.2 LOr atiox Faron? Thur de AE Rongelup (Group 1) ol... 39r Afiinginae (Group JI}....)50 72r Rongcrik (Group Pils... . Vtirik (Group IV). 0202. . 1 | 1 TOr | 125 Shr 20 Gr 1W6r War The dose values given in Table 1.1, based on film badee, meter and monitor data, are consistent with a constant fallout hypothesis of about 12 hours effective time.” One exception isinade: Che dose values for GroupIIT are about 79 percent of the 12 hour fallout value, averavwed for 28.4 and 34 hour exposures. This was felt to express most accurately the average air dose On Rongerik (Group IIT) a set of Alm badge readings were obtained which constitute the only direct evidence of (otal 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 u steel refrigerator, read 38 r. These dose values represent a variety of conditions, but. considering the shielding and attenuation fnclors, are consistent with the assumption that the dose outsidg during the first 28.5 hours after the beginning of the fallout corresponded to about 12 hours of constant fallout. 9002 ibs received by personnel who spent roughly half their time inside structures where the dose rate wis liter fonnd to be roughiv half that out- doors. On the otherislands such shielding wag not available. Figure 1.8. illustrates the cumulation of radiation dose asa function of tone after deto- nation. ‘The dose rate varied comtinnuons)y. The major portion of radition was received at the lugher dose rate prevailing in the early por- tion of the expocure period. Tdy che time that "Using 22 hours achially results in vadues which sre hivher than these of Kable 2.) hy 3 te l)or, Tatde 2.1 listine the valves calcultted leefore all speetrum) dicts wis avadhabde. Uncerteinty iu all the infuurmation i+ greuter Chany this difference, which is neglected,