cS~ ” ue ae PPaBntet pm ee A F __ = swcbet=! 0! bi £ CORI DIN RS * egy * 4 Feat, ile: ondzes were -wornrnywrelativelylarge “ities of cesual visitors to the contaminated x, second, the limitations of photoiim dosimetry preclude the measurex doses below 50 mr. If the lowest dos- age group is excluded from the data in an at- tempt to obtain a better estimate of the average dose received by those actively associated with the tests, a value of 473 mr is obtained. The members of TU 3.1.5 received an average radiation dose of 1,320 mr. This average was derived by considering all personnel of the unit, but, since some were laboratory personnel who received practically no exposure, the average dose received by the monitor group was somewhat higher. The three films mentioned in Sec. 2.3 were from members of an LCM boat crew who, on E+2 days, made a trip from Parry to Engebi, Muzin, Bokon, and Teiteir. Three of the crew of four had film badges and pocket dosimeters. One man had an ionization chamber survey meter and acted as monitor for the party. He states that at no time did the meter read more than 40 mr/hr but that all 200-mr dosimeters were off scale at the end of the trip. Two civilian scientists making the trip had film badges which showed 170 and 185 mr. The clothing worn by the men with the high film badge readings showed only 3 mr at the end of the trip. A series of tests was conducted to determine the accuracy, with fission product exposure, of film badge data compared with readings of quartz fiber pocket dosimeters. A Victoreen thimble ionization chamber, known to be rea- sonably energy independent, was used as a standard of comparison. It was found that a film badge reading of 100 to 200 mr had a low significance, owing primarily to the variable exposures received by all unused film badges during the Dog day fall-out. Readings above 400 mr agreed with the standard chamber within about 10 per cent and were considered to be reliable for doses equal to or greater than 400 mr. 2.7.4 External Radiation Doses to 15 May 1951 An analysis of all radiation exposures as shown by photographic film badges was made as of 15 May 1951. The exposure data presented represent only that received during various missions connected with shots Dog, Easy, and eee “im, Agee NAad ST as = nent re CeET “Géorge. The tetal radixtion exposur~3 were higher than the figures shown vy about 1,850 mr, which is the estimated average integrated exposure received from the Dog shot fall-out. Film badge data available from 3,180 individuals show an average dose of 422 mr. Figure 2.10 shows the distribution of doses. If casual visitors are eliminated from the list, the average dose received by 2,235 persons is 600 mr. The members of TU 3.1.5 had received an average dose of 2,060 mr. 2.7.5 External Radiation from Fall-out following Item Shot At approximately 43 hr 20 min the gamma intensity recorder at the radiological safety building, Parry, showed a sharp rise followed by a drop to nearly the original reading. This “spike” was interpreted as the result of the passage overhead of an active cloud from which little material fell out. Several other spikes of activity appeared during the next few minutes, followed by a steady rise in activity due to fall-out, until about 14 hr 45 min. Fall-out started again at I+8 hr and continued until 1+13 hr 45 min. From 1+16 hr the activity decayed according to a t~? law. A continuous record of gamma ray intensities was maintained. Figure 2.11 shows the increase and decline of gammaintensity outside the radi- ological safety building as a result of the Item shot fall-out. Starting at I+12 hr, the integrated dose out-of-doors was determined by using pocket ion chambers and photographic film badges. These were placed at locations representative of conditions on Parry. The integrated dose was determined by numerical integration of the intensity curve in the early stages of the fall-out and from direct dose measurementsin the later phases. Figure 2.12 shows the cumulative dose curve. An incomplete but reasonably representative survey of Eniwetok Island indicated that the fall-out situation there was almost identical with that on Parry. No data were available from Japtan. Assuming that decay continued according to tt? it was possible to predict total doses for future times. For 115 days the total expected dose out-of-doors was 7,370 mr, and for #30 days it was 9,520 mr. It should be emphasized that these doses would result from the Item WELBte. = eresee or We a oe