2.3 On-Site call-out Fall-out on Entwetok and Parry islands was observed only once from devices fired at Eniwetok Atoll. Approximately two hours after detonation of thef_ Mohawk}device on Eberiru Island, an increase in background was noted on Parry fsland. The fall-out, which waa light, continued for approximately one hour, Penk Intensity, reached at the end of the fall-out, was 22 mr/hr. Ruin showers later tn the day effectively removed most of the contamination. The onlv significant fall-out observed on Eniwetok and Parry islands during the operation resulted from the (__ TEWA “device fired on Bikini Atoll, The fall-out on Eniwetok commenced approxffmately nine hours after the device was fired. Two peak Intensities in air concentration were ob- served, ay shown in Fig. 2.11. The increase in the background was quite rapid, with a peak of 100 to 120 mr/hr throughout Parry Island. During the fall-out period, which lasted approximately 17 hr, several rain showers oc- curred; rain samples assayed showed counts in excess of 5,000,000 disintegrations per minute per Hter. The gamma background Ievel fell off quite rapidly once the fall-out ceased. It Is to be noted in Fig. 2.12 that the background decay was much more rapid than that expected from the normal exponential decay until H +48 hr and later. Clean-up operations after the tall-out were conducted around living and recreation areas. As a result of the rain showers, hot spots were found around cach building where rain runoff collected. These hot spots, along with other contamination on the surface, were most effectively reduced by using bulldozers, read scrapers, and hand-grading operations to turn the sand. The decontamination efforts were successful in reducing the level to such that no ons exceeded the 300 mr/weck tolerance level, Most serious effect of the fall-out was delay of the roll-up operations. Initially, personnel from H&N whose dosage records indicated that they were near the Ilmits of 3.9 > were flown out to Bikini to remove them fror. the contaminated area. Generally, people In this category were urgently required for roll-up. Accordingly, the maximum permissible exposure for the operation was raised to 7 r. This allowed roll-up to proceed without further delay. On the average, the dosage received by any one tndividual on Eniwetok or Parry Islands as a result of the fall-out varied from 2 to 3.5 r, depend- ing on the length of stay of the individual and the type of work in which he was engaged, In general, those working in jobs requiring them to remain outdoors during working houra were at the upper end of the dosage spread. During the actual fall-out period, personnel were requested to remain indoors ag much as possible and to take full advantage of shower facllitics. Of interest is the fact that no evidence of grossa personnel contamination was observed as a result of this fall-out. - 26 -