Seem em em ret oe Fem lens Rte et eats ey TABLE 2.5 DISTRIBUTION OF ACTIVE PARTICLES Muzin Nautical miles from zero Bearing (degrees) Maximum mr/hr H+hours at maximum Hours to 50% fall-out Velocity (1000 ft/hr): From distance From time Compromise Mr/hr at 100 hr Particle diameter (microns) Initial % in cloud La 135 1,000 0.85 0.85— 45 47+ 47 6.2 240 14 2.6.7 Air Sampling on Destroyer, Easy Day In an attempt to secure further data on the nature of the fall-out material, a study was made on the USS Walker during the hours following Easy shot. Commencing at H-hour and during the next 12 hr, the ship pursued a course due east of Engebi, running from 10 miles east to 15 miles east and then returning on the same course. On the night of E~1 the background level on the deck was 0.1 mr/hr. This same level prevailed prior to the shot on E-day and until 1130 hr when it began to rise rapidly, reaching a maximum of 6 mr/hr 63 hr after H-hour and then declining slowly. Immediately after the shot, air sampling was begun by drawingair through filter paper wrapped around a Geiger tube probe. This showed no increase in activity on the filter paper until the general rise in the background at 1130. Immediately after this the filter paper activity showed a rapid rise. A cascade impactor sample (CI-1) was taken from 0950 until 1125. At 1225 a second cascade impactor sample (CI-2) was started and ran for lhr. At 1350 p.m., sampling was started with the molecular filter (MF-1), and this was run for 75 min. Since by this time the background was decreasing, no further samples were col- lected. The air samples obtained were counted on E+1 day in the morning. No activity greater than background was found on any of the five. ce we ‘-* ce te mR te nM EN ER ew a aneTa Map Ma ~ nn nape ae Kirinian 1.6 130 1,100 0.9 0.9- 31 44+ 40 9.4 210 21 Bokon Biijiri 2.8 6.0 125 2,000 120 180 1.0 1- 8 6 18 40+ 30 16 180 7.2 125 40 10 14 8 7 8 6.6 95 36 Piiraai 15 7 3 5 5.0 15 11 Runit 10.5 130 4 27 23 5 2 3 0.95 60 2 Stages of CI-1. In CI-2, taken during the background rise period, there was no activity appre - ciably above background on stages 3, 4, or 5. Stages 1 and 2, however, contained too much activity to count the first day. However, on E+2 day, counts of 35,800 c/m and 16,800 c/m were obtained on stages 1 and 2, respectively. The counter efficiency was approximately 7.6 per cent. The molecular filter sample taken from 1350 to 1505 showed a level of activity on E+1 day which was not significantly greater than background. Since essentially 100 per cent of the activity on CI-2 was located on the first two stages, a search was made for particles. Portions of the slides were blocked off by means of glass slides, and the activity was checked with a survey meter. On both slides the activity was found to be highly localized. The active areas were then searched under the microscope. On slide No, 1 two particles were found in the active area which were similar in appearance to those previously isolated from soil samples in fall-out areas after Dog shot. One such particle was found on slide No. 2. Removal of each of these particles by means of a needle point showed them to be highly active. Recounts of activity remaining on the slides showed that the levels had dropped to less than 1 per centof the level obtained before removal of those three particles, Size measurements with the eye-piece mi» &kometer showed the active particles to be 200 we eee te —_ - -