Sider in close differenc ~ften strongly suggest their existence. Usually the ASEL- and std-GITR’s are * since, when properly oriented toward surface zero, there are only small ponSe as a radioactive cloud approaches. A seconc ...erence shown by both the sec- and ASEL-GITR’s with respect te the std-GITR is best illustrated by the records obtained from Umbrella Stations D 4.8 and DRR 3.9 (Figures 3.21 and 3.23). The ASEL- and sec-GITR’s track each other after the peak dose rate but rise above the td-GITR trace. Similar differences are also seen for some records at 0 to 15 minutes and 0 to 6 hours presented in Sections 3.3.2 and 3.3.5. Although changes in detector response as the radiating cloud recedes might be a contributing factor, these differences are most probably due to the combined effect of radioactive materia on coracle surfaces and in the water immediately surrounding the coracle. The center of the sensitive volume for the std-GITR stands 14.7 inches above the coracle deck whereas those for the sec-GITR and the ASEL-GITR are about 3 inches above the deck; thus, the relative effect of deck deposits is greater for the lower detectors. An empirically determined curve (Figure C.18) indicates that the response of the lower detectors should be about three times that of the std-GITR. The ratio between the recorded dose rates for these instruments at Stations D 4.8 and DRR 3.9 does approach this value as the downwind segment of the base surge recedes. Radioactivity in the water can cause an even greater difference between the std- and sec-GITR records and is undoubtedly the principal cause at later times; however, at these early times the visible boundary of white water (Appendix F) has not yet reached these stations. Unfortunately, the combined effects of overturn, washoff at close-in positions, and the relatively light deposition over the more distant array afford insufficient opportunity to check this hypothesis. The remaining differences in the composite records cannot yet be satisfactorily explained. The flat plateau shown by the ASEL-GITR at Station CL 3.1 on Umbrella (Figure 3.16) may have been produced by a radiating cloud that passed off to the right of the station through a region of . low directional response; however, the suggestion raises nearly as many difficulties as it solves. The 15-second dip occurring between 32 and 47 seconds in the sec-GITR record at Station D 2.7 on Umbrella (Figure 3.20) may be due to capsizing, although this possibility seems unlikely, since the std-GITR record appears reasonable until 2.4 minutes. The early gamma records obtained abvard the target ships are not necessarily comparable with those obtained from the coracles, because little is known of the directional response of GITR’s installed in such complex surroundings. The shipboard records are in general agreement with those obtained from the co.acles although most of the Umbrella records are incomplete because of saturation. The maximum dose rates for some saturated records have been estimated from the records of GITR’s installed inside the ships by Project 2.1 (Reference 86) and are presented on the appropriate plots. The initial radiation recorded at stations closer than 6,000 feet during both Wahoo and Um- , brella was a sharp peak in dose rate occurring at about the time the explosion bubble first reached the ocean surface. Usually it was recorded as a Single radiation pulse by both the ASEL- and std-GITR’s. Unfortunately, the first radiation pulse on an ASEL record cannot be considered valid, since any leakage occurring between the warmup signal at minus 5 minutes and the first pulse must be included as an indeterminate part of the initial dose increment. Consequently, the initial dose rate peak has been omitted from the ASEL records except when substantiated by more than one radiation pulse. All initial dose rates obtained from the ASEL records have been included in Table 3.4 and in Figure 3.4 to show the extent of Scatter. Because the std-GITR ion chambers are recharged by the minus-5-second signal, their records are considered reliable. Although a plot of these initial dose rates versus distance exhibits considerable scatter, the std-GITR peaks and some of the ASEL peaks are reasonably approximated by a straight line whose slope is similar to that for the attenuation of gamma radiation with distance from a distributed source of mixed fission products at early time (Figure 3.4). Note that the initial dose rate peaks measured by the ASEL-GITRat Stations CL 4.6 and CR 4.1 during Wahoo (Figures 3.7 and 3.9), both of which are substantiated by more than one radi- ation pulse, show an attenuation with distance that is too great unless a point source of radiation 86 Pages 87 and 88 deleted.