In the rocket samplers, some breakup!of the fallout particles was thought to be likely during s carried passage through the shock front in the diffuser throat. A series of the experiment tube at the University of out by the Naval Radiological Defense Laboratory (NRDL) in the shock fallout grains were not fractured California Engineering Experiment Station indicated that coral another possible cause of by Mach-2 shock waves (Reference 70). Impact with the filter is is known aboutthis effect. nothing or particle breakup in all the sampling devices, but little 2.3 FIELD OPERATIONS samples to be used for the deter2.3.1 Meteorology. It was indicated in Section 1.3.3 that collect ed from the light and variable minationfalloutpartition by the UCRL method should be layer, if well defined, or from higher locations in the cloud. The cloud heights and wind structure in the upper atmosphere were therefore important characteristics to consider in devising operational plans. It was known from previous work that the clouds rise to a maximum altitude in the first few minutes and then settle back to a stabilized level. Based on height-yield curves derived from photographic data on earlier shots (Reference 22), it was estimated that the stabilized altitudes would be around 72,000 feet for Shots Koa and Walnut and 99,000 feet for Shot Oak (Reference 71). The altitudes observed by project aircraft were considerably lower (Reference 16). A radar record for Shot Koa indicated that the cloud rose to 72,000 feet at 5 min- utes and then settled rapidly (Reference 72). The light and variable layer existed for all the shots, being poasibly best defined for Koa where it circulated over the atoll for at least a day. For Koa and Walnut, the altitude of the layer coincided quite closely with the top of the cloud, whereas for Oak it was some 20,000 feet below the top, which was blown off rapidly by the strong easterly winds. Because the B-5S7D samples were taken from this stratum in each case, the criterion of sampling from a region that would not be receiving fallout from any other source was easily satisfied. Some altitude data taken in part from the wind and temperature tables in Appendix D is given in Table 2.2. The suitability of the wind structures for fallout sampling along height lines can be most readily visualized by reference to the plan view, wind velocity hodographs at shot time (Figures 2.9 through 2.11). The hodograph for Koa shows that the winds were ideal for height line sam- pling, because material falling from the light and variable layer would be clearly isolated from the rest of the fallout. For Walnut, an overlap of particles originating in the cloud at 40,000 feet and at higher levels would be anticipated. For Oak, the samples collected at 1,000 feet would contain material that came from several different elevations in the cloud. 2.3.2 Shot Koa. No rocket samples were collected from Shot Koa. In preshot planningit was intended that a salvo of 18 rockets would be fired into the cloud, 6 each from Sites Wilma, Sally, and Mary. The firing line to Site Wilma failed on the day before the shot and could not be repaired before evacuation. Firing circuits to Sites Sally and Mary were intact at shot time, and a firing signal was transmitted to these sites at H+7 minutes, but no rockets fired. Evidently, the heavy current drain by several launcher orienting motors caused the main power supply voltage to drop to a point where it was insufficient to operate critical relays in the local launch-programing equipment. Thereafter, launching operations were programed go that only a Single launcher motor would be operating at one time. : Five samples were taken from the cloud by B-57D aircraft at 4Y,, 6Y,, 8, 11, and 29 hours postshot time (Table B.1). A flight scheduled for 13 to 14 hours had to be canceled becauseof rain and atmoshperic turbulence. The first four samples were collected in about ¥, hour each, and the last sample required 2, hours. The wing tank samplers functioned on each flight, but there were no gas gamples on the last three runs because of a failure of the compressor pumps on the coincident sampling units. Samples of material falling from the 60,000-foot layer were callected at an altitude of 1,000 feet at 4, 6, 8, 10, and 12 hours after shot time by a WB-50 aircraft. The fallout was encountered. ona bearing of 50° to 60° at 28, 59, 88, 109, and 131 miles from ground zero. A second 24