——= “= = SSSA TION Neer eee ” equipment abort ne Gestru.s> . *Ses324 -ptanaity of Radiation from Dog Shot ” ~~"“FsT-out on Parry and Japtan and an aerial a eT TE BB aR ae : 5 eas Sem ts fe. a, ‘s nLy, How, a stand-by kos mnared 2a 4t 6550 D-day the background count, on reFor George ahr-: only the Re P 3 tes.ee cording rate meters operating with gamma ray each case the 2-17 carries the fdlh aapoment counters in the radiological safety building, of cloud sampling equipment except ctx. snap Parry Island, rose precipitously. These sampler. On the first missicn, becaure of counters were set at a relatively high sensisome difficulties associated with the change tivity and went off scale so that the first phase from automatic te manual operation, =li the of the fall-out was lost, but the rate of rise was equipment wasnot utilized to the fullest advanobviously very rapid. The recorders were tage. All the activity collected after Rasy shot brought on scale at 0915, and one was operated by the air sampling equipment on the destroyer until the activity due to fall-out had dropped to was contained in three large particles (80, 100, a relatively low value. Fall-out continued until and 200 microns in diameter). Details are given about 1400 D-day. Figure 2.1 shows the build-up in Sec. 2.6.7. of the fall-out. With neither the destroyer nor the B-17 were At about 1000 a survey of Parry Island was intensities found comparable to those of Dog made with an ionization chamber survey instrushot. The B-17 found an irregular distribution ment. Although there were some smal! areas of of low activity averaging about 2 mr/hr. The Project 1.7 (wing) filter contained many active particles, but only a few could be isolated on account of difficulties in extraction from the paper. Those isolated were 50 to 100 microns ‘in size. Flight statistics are given in Sec. 2.6.8. The results of the gammaintensity survey conducted for George shot were eminently satisfactory. Fall-out was detected at the predicted time and location. The time and intensities were nearly the same as those observed on Parry after Dog shot. The area of search was limited by rain squalls. There is no assurance, therefore, that the observed maximum of 150 mr/hr was the maximum existing in the vicinity. However, even a maximum as low as 150 mr/hr at 60 miles, 24 hr after the shot, has important implications. Both theory and observations indicate that intensities several times greater would exist at ground level after the material had settled on the ground. For Easy shot, the intensity observed on the deck of the destroyer was much greater than anything observed with the B-17. In the cascade impactor on the B-17, almost all the activity was collected on the first stage. The active particles could not be isolated because of a prior agreement not to disturb the material before it was shipped back to the owners, However, the active region of the plate was localized, and it was observed under the microscope to be occupied mainly by a few particles of 50 to 100 microns in diameter. Sates eae ee ee rireaot eter epmpanseine) ORs > ime irenanee eae prwoveein ami re NI er marge me pe ~ relatively high activity (up to 1,000 mr/hr), the island as a whole showed a rather uniform level of contamination. Decay curves indicated a possible component with a 7.7-hr half life followed by a decay fol- lowing a t™'-? law (see Fig. 2.2). The maximum intensity for Japtan was estimated from survey meter readings to be about 10 per cent greater than that on Parry Island. No comparable data are available from Eniwetok Island, but survey meter readings made early in the fall-out showed intensities about two thirds of those on Parry Island. 2.6.5 Particles from Dog Shot Fall-out on Atoll The method of studying the particulate size of the fall-out on Dog shot, as finally decided upon by the radiological safety laboratory, was one of mechanical separation. Samples were collected from spots showing activity higher than the average of the surrounding area. The sample was then divided and subdivided many times until it was indicated by the use of a portable Geiger counter, beta window open, that one portion of the material contained moreactivity than the eorresponding portion. Further division was required, following the activity closely, until the last separation was made onto a microscope slide by the aid of a 2-mil wire. Approximately one hundred such separations and isolations of active particles were made. The size of the particles could only be estimated at first because no micrometer was