amounts of induced C1™ (Reference 107); decontamination studies (Reference 108); and plume . trajectories (Reference 109). 3.5.1 Fractionation. Fractionation is indicated by the pronounced differences in decay curves obtained from the various samples collected by the project. To establish the importance of the radiation due to deposited material relative to the free-field radiation during base surge transit, some systematic means of correcting for possible fractionation of the deposited material was required. Coracle recovery operations prevented the counting of IC collections at times earlier than about 11.5 hours on Wahoo and about 13.5 hours on Umbrella. Since decays could not be rua on each IC tray, there did not appear to be any reliable means of correcting the observed counts back to the time of deposition. A detailed examination of the IC decays Suggests, however, that the observed fractignation has some regular correlation with the history of the radioactive material immediatety prior to collection. It should be emphasized that these analyses of decay characteristics are made upon limited observations. Nevertheless the apparent trends seem at least sufficient for the purposes of this project, especially since conclusions based upon this data are supported by information irom other sources (Section 3.3.1). IC trays that were continuously exposed or that are known to have been altered by coracile overturn have been eliminated from consideration; thus, only 21 decay curves for representative 1-minute IC collections (Table 3.34) are available for comparison. The 37- and 40-minute collections from Station CR 2.7 for Umbrella are also included in this group since, although the coracle is reported as overturned, the IC cannot have operated in an overturned position to expose these trays. Nevertheless, these coilections are probably the result of an arming error and thus represent those of an overturned coracle, in which case they should most resemble the “water’ decay described later. Each IC decay was potted from 0.5 to 60 days on a separate sheet of transparent semilogarithmic paper, using identical scales; smooth curves were then drawn so that they passed through all plotted points. By comparison of these curve shapes on a light table, it was found that the curves could be grouped into two general classes whose characteristic shapes could not be superimposed. No real distinction between collections from the two shots could, however, be made. These decay curves have been assembled into two families and normalized at 22 days (a time which produces the narrowest pencil of lines between 20 and 40 days) and are presented in Fig- ures 3.216 and 3.217. The family of decay curves represented in Figure 3.216 is typical of collections that were probably deposited directly from transiting airborne material; whereas that in Figure 3.217 is typical of collections that could only have resulted from some secondary process, such as radioactive water splashed into the collector. These two characteristic types of decay were, therefore, called the “ base surge” or “early” decay and the “water” or “late” decay, respectively. For ease of comparison, 2 best line has been faired through these two families of curves, and these two lines together with the standard decay curve and the gamma- intensity-decay unit (GIDU) decay curve obtained by Project 2.1 (Section B.2) are presented in Figure 3.218. Note that the early collections approximate the standard decay curve prior to 22 days, whereas the late collections approximate it from this time to 60 days. One Umbrella collection (DL 16.0 at 6 minutes) does not follow any of the decay curves over the entire 60-day interval. The collections from DL 16.0 and D 22.0 for this shot are both so close to background that their decay curves may have been influenced by changes in counter background. Other decay curves obtained from IC trays that jammed in an exposed position or from other collections that were continuous throughout the event are presented in Figure 3.219. These curves possess a variety of shapes, which vary berween the early and late characteristics. In addition to this possible division into two families, there also appears to be characteristic subvariations in the shape of the base surge decay family (Figure 3.216). A more detailed comparison of the carves for Wahoo and Umbrella samples indicates that a further subdivision may be possible (Figures 3.220 and 3.221). The collections corresponding to the plotted.curves are given in Table 3.34. Although the correspondence is not perfect, there is a fairly consistent change in curve shape with time of deposition, particularly for collections widely separated in 320 [@r