LONG-RANGE FALLOUT FROM SEDAN AND SMALL BOY minimize been 87 redispersion by the wind of the debris which had already collected. Each collector was exposed for a 72~-hr sampling period. After postshot notification from the Nevada Test Site as to the expected arrival of the clouds at each of the three samplinglines, sampling was begun about 12 hr before the estimated arrival time. These time estimates were based upon the latest meteorological and survey data available. Figure 4 shows the Weather Bureau’s trajectory of the Sedan cloud. There was a wind sheer of the original cloud at 10,000 and 16,800 ft; the higher level of the cloud traveled slightly north of the lower level and at a faster velocity. Both levels of the cloud were intercepted by the mobile line. For the Small Boy shot (see Fig. 5), a wind sheer occurred at 10,000 and 16,000 ft with the 16,000-ft level traveling at a faster velocity than the 10,000-ft level. The two levels crossed at the northern end of the mobile line although the higher level arrived at the stations about 12 hr before the lower level. MEASUREMENTS All samples collected from both shots were radioassayed on a 3by 3-in. Nal(Tl) crystal in conjunction with a 400-channel pulse-height analyzer. The fallout collectors were scrubbed with chloroform and a rubber squeegee to remove all debris from the collection surfaces. The resultant mixtures were evaporated to dryness in 500-ml nickel crucibles and ashed over a Meeker burner. Any rain or other contents of the 5-gal drum associated with each collector was combined with the material in the crucible. The mixture in the crucible wasfinally evaporated to dryness and assayed on the 3- by 3-in. crystal. The total gamma spectrum of each sample, including preshot background samples, was obtained by these measurements. The inte- gration of the activity beneath the spectrum after subtraction of detector background represented the total gamma activity of each sample. Selected filter papers were dry-ashed at 440°C, refluxed in nitric and hydrofluoric acids, and dissolved in nitric acid. Specific falloutcollector residues were fused with sodium carbonate and dissolved. These solutions were then analyzed radiochemically for a number of radionuclides. In the interest of brevity, only the results from the mobile lines are discussed in this paper. Although debris from the shots was recognizable at the fixed stations, it was much less pronounced, and measurements of it were greatly complicated by back- ground levels.