90 KREY AND FRIED component. Activities on the third day of sampling are lower by a factor of 2 or 3 than those on the previous day; the distribution of concentrations approximates that of the first day of sampling. The total gamma activities of the Small Boy mobile-line stations (north to south) corrected to 1130 hr on D +1 but uncorrected for background contribution are shown in Fig. 8. The preshot air filter was counted on D+ 4, whereas the background fallout collector was assayed on D+ 9. The background could have amounted to about one- half the total activities in the postshot samples, particularly in the southerly stations. However, the presence of fresh debris is clear and the relations between Samples should not be seriously hampered. Figure 8 shows a maximum in total gamma activity at the northern extremity of the line for the fallout-collector samples and for each of the three days of air sampling. It is evident that the mobile line was situated too far south to provide for a central interception of the cloud. Furthermore the increase in activity concentrations on consecutive days along the southern sector of the line indicates that sampling in that sector was discontinued too early. Gamma-spectrum Analyses The gamma-spectrum analyses did not uncover any pronounced effects except for the presence of induced '*'W in the Sedanfallout. Particular attention was given to identifying “Na in the Sedan underground-burst debris, but none could be found. The spectra permitted easy identification of fresh debris, and they verified the conclusions drawn from the grosS gamma CUneiderations. & COMparisun of the spectra from the two shots is given in Fig. 9. The spectra ot two air-filter samples collected at about the same time after each shot and assayed at about the same elapsed time after each detonation are normalized to the 1.60-Mev photopeak of 407 4, Weaker energy emitters, possibly associated with '’Te, 17, 1, Mo, Ru, and *Ru, are in slightly greater abundance relative to 14074 in the Small Boy debris than in the Sedan material. However, as was observed, these differences did not bring about any marked variations in the rate of gamma decay of the debris from each shot. Sedan Radiochemical Analyses It was found that the measured pre-Sedan shot levels of “Sr, "Y, %Zr, 1°6Ru, and “4Ce at the mobile line which resulted mainly from stratospheric fallout represented a large fraction of the total activities of these nuclides collected in post-Sedan samples, It is likely that the background levels vary significantly from day to day depending upon local meteorological conditions. Therefore, the background levels determined for a period of time at one location on the sampling line