Se = = ~ é EUSENEORMAT wes, ' Oo al oe Le o F ntlitnatiatnaidl AL os tee alge. ard 190 w.cron: onange the Na. 1 side ay Bd aE onaneaeas aerialPurves We one ANE? armament ductedfromH+2 toH+3 hr. P52 2 . cong ox tie No, 2 slide. Agsu:.2ang|th® asual cray curve these gartic‘es mit’ have had an 500 ft in the area shownin zug. 3. fans. US observed are shown in Figs. 2.5 and 4.4 activity of approximately 1 pc each. The volume of the air sampled was 1.05 cubic meters, From the rather close agreement between the These particles were distinctive in shape and locations of the predicted and observed fali-out, general surface appearance. Despite the presthe following rough estimates can be made con- ence of other dust particles on the impactor slides, the active particles could be immediately singled out on a basis of appearance alone once the general active area was located. Since these particles were obtained from the air, the activity was already attached to the particle before it reached the ground. Since the size, shape, and appearance of these particles were similar to those previously isolated, this would seem to confirm the assumption that the previously isolated particles were airborne also. 2.6.8 Aerial Search for Heavy-particle Fallout On Easy day an aerial survey was conducted from H+34 hr to H+53 hr. The B-17 flew at cerning the altitude of origin of the fail-out, the particle size, and the relative amounts of active material. The two smal! peaks in the southeastern part of the area of search are excluded as too close to the border of the predicted fallout to be reliable. The counts obtained by the cascade impactor before the slides were returned to Project 6.1 for shipment to the Zone of Interior on G+1 day appear in Table 2.6. 2.6.9 Number of Active Heavy Particles Needed for Dog Shot Fall-out Can large particles, of a kind needed to account for Dog shot fall-out on Parry, exist without having been observed in previous cloud- 500 ft in an area 20 miles east-west by 15 miles sample studies? east of Rojoa. Intensities observed were: minimum 0.7 mr/hr, maximum 5.0 mr/hr, and aver- OM means“of the order of magnitude of.” As one starting point in the discussion, it is north-south with the center of the area 10 miles | age 1.85 mr/hr. Within 2 miles of the destroyer Walker’s course from H+32 hr to H+4 hr, in- tensities observed were: minimum 0.9 mr/hr, maximum 3.5 mr/hr, and average 1.85 mr/hr. TABLE 2.6 NET COUNTS PER MINUTE WITH A COUNTING EFFICIENCY FOR UX, BETA OF 8.8 PER CENT To abbreviate, in the ensuing calculations, taken that previous cloud-sample observations indicate a typical particle size, OM 5 microns, and that the characteristics of these particles are consistent with the assumption that they are produced by the scavenging of most of the fission atoms by DM 100 tons of vaporized tower and bomb material. Under these condi- tions, the numberof small particles is OM 10°. The activity associated with particles of typical size, a few hours after shot time, is H-hours Stage 64 114 244 26 1 2 3 4 5 7,464* 642 196 42 52 8,538* 353 107 17 42 4,538* 228 54 39 72 4,305 150 63 15 19 *These counts were made before the active area of the slide had been localized and are very unreliable. The area of impaction was visible on the other slides, which could therefore be properly positioned under the counter window. Background counting rate, 37 c/m. taken as OM 10° yc/10" particles, which equals 107° tc/particle. As anotherstarting point, it has been found that the observed variations in surface intensity cannot be accounted for if the surface con- centration of Dog shot fall-out particles on Parry and neighboring islands was substantially in excess of 1 particle/sq cm, or 1,000 parti- cles/sq ft, or OM 10" particles/sq mi. Also the intensity observed on Parry following Dog shot was such as to require a surface activity OM 10!yc/sq mi, or 1 pc/particle/sq cm (ob- served activities of isolated particles agreed with this value).