Chapter 4 DISCUSSION 4.1 SHOT CHEROKEE Because the residual radiation level from Shot Cherokee wastoo low to be of any military significance, the results were omitted from Chapter 3. However, this should not be interpreted to mean that no fallout occurred; the evidence is clear that very light fallout was deposited over a large portion of the predicted area. Partly to obtain background data and provide a full-scale test of instrumentation and procedures, and partly to verify that the fallout was as light as anticipated, all stations were activated for the shot, and all exposed sampling trays were processed according to plan (Section 2.4). Smali amounts of fallout were observed on the YAG 40 and YAG 39; the collectors removed from Skiffs AA, BB, CC, DD, GG, HH, MM, and VV were Slightly active; and low levels of activity were also measured in two water samples collected by the SIO vessel DE 365. Results from all other stations were negative. The approximate position of each station during the collection interval is shown in Figure 4.1; more exact locations for the skiffs and project ships are included in Tables 2.3 and 2.4. The boundaries of the fallout pattern predicted by the methods described in Section 4.3.1 are also given in the figure, and it may be seen that nearly all of the stations falling within the pattern received some fallout. (Skiff PP and the LST 611 probably do not constitute exceptions, because the former was overturned by the initial shock wave and the incremental collectors on the latter were never triggered.) On the YAG 40, an increase in normal background radiation was detected with a survey meter at about H+6 hours, very close to the predicted time of fallout arrival. Although the ionization rate never became high enoughfor significant TIR measurements, open-window survey meter readings were continued until the level began to decrease. The results, plotted in Figure 4.2, Show.a broad peak of about 0.25 mr/hr centered roughly on H+9 hours. In addition, a few active particles were collected in two SIC and two IC trays during the same period; these results, exPressed in counts per minute per minute as before (Section 3.2.1), are given in Figure 4.3. The Spread along the time axis reflects the fact that the SIC trays were exposed for longer intervals than usual. Radioautographs of the tray reagent films showed that all of the activity on each one was accounted for by a single particle, which appeared in every case to be a typical slurry droplet of the type described in Section 3.3.2. Successive gamma-energy spectra and the photon-decay rate of the most active tray (No. 729, ~6,200 counts/min at H+10 hours) were measured and are presented in Figures 4.4 and 4.5. the former appear to be due to Np?*, The prominent peaks appearing at ~ 100 and 220 kevin A slight rise in background radiation was also detected with a hand survey meter on the YAG 39. The open-window level increased from about 0.02 mr/hr at H+10 hours to 0.15 mr/hr at H+12 hours, before beginning to decline. Only one IC tray was found to be active (No. 56 ~9,200 counts/min at H+10 hours), and this was the control tray exposed on top of the collector for 20 hours from 1300 on D-day to 0900 on D+1. Although about 25 small spots appeared on the reagent film, they were arranged in a way that suggested the breakup of one larger slurry Particle on impact; as on the YAG 40 trays, only NaCi crystals were visible under low-power Optics in the active regions. Plots of the gamma-energy spectrum and decay for this sample are included in Figures 4.4 and 4.5; the similarities of form in both cases suggest a minimum of radionuclide fractionation. 113