detonations. In Some cases where radiation fields of tactical Significance were still being recorded at 15 minutes, the record is extended. All dose rates presented have been corrected for response aS described in Section 3.1.1. No corrections have been made for deposited activity (Section 3.3.1) or for waterborne radioactive sources, Viz, (1) radioactive material remaining suspended after being deposited from the base surge, (2) water directly contaminated bythe device, and (3) radioactive foam generated during eruption and callapse of the column. Since the presence and relative importance of these sources cannot be precisely determined, the unmodified gamma records are presented with a brief discussion of possible errors. The extreme complexity of the gamma records, especially those for Wahoo, fosters the Suspicion that at least the minor variations are generated by the detecting instrumentitself. This suspicion is not sustained by a comparison of standard and secondary GITR records. When the UW-GITR detector failed to drop, a second record, called sec-GITR record, was produced by a completely independent instrument at the same location. Where such dual records were obtained, the two nearly duplicate each other (Figures 3.75, 3.76, 3.81, 3.88, and 3.89). The slight variations between these two records are usually explained by the differences in position and response of the two detectors (Section 3.1.1 and Figure 1.2) or by the fact that the coracle overturned. The following interpretation of the gamma dose rate records is based, therefore, on the assumption that both the variations in the recorded dose rate and all differences between two instruments at the same location de in fact represent actual changes in the radiation field. Before further examination of the gamma dose rate records is attempted, the fact that many of the coracles were drifting after Wahoo and that many were overturned after Umbrella must be considered. Both occurrences could severely modify or even vitiate the gamma records affected; however, a careful evaluation demonstrates that very few records are greatly changed. All coracies that broke free after Wahoo were dragging long lengths of mooring cable, which greatly diminished their rate of drift (Section 2.3.2). In each case the rate of drift has been estimated and coracle movement during surge transit has been calculated (Table 3.11). In.no instance does this distance exceed 200 feet, which is less than the theoretical limits placed on coracle positioning accuracy. Care must, however, be exercised when interpreting the later records, since some coracles drifted with the white water (Appendix F) while others became entangled with various elements of the target array. This information on later behavior is summarized in Table 2.6 and Figure 2.1. Coracle overturn after Umbrella represents a more serious difficulty; however, if the stdGIR was not damaged during overturn, an attenuated record is obtained through the coracle bottom, which is sufficient for an analysis of surge transit if alowance is made for possible masking by white water. This attenuation factor has been evaluated at 0.18, using the known std-GITR response through its own electronics further attenuated by the coracle components (Section A.1). The sec-GITR in the capsized position is prevented from obtaining an accurate record of the radiological event through the bottom of the coracle by a layer of water that var- ies in thickness from 0 to about 5 inches depending on wave action. The time of coracle over- turn is difficult to estimate, since a rapid decrease in dose rate may indicate either a rapidly transiting surge or an overturn. The estimated times of overturn (Table 3.11) are determined by comparing the GITR records of all adjacent stations. Where there is good agreement with neighboring stations, both coracles are assumed to be upright; where the two records do not track, an overturn is assumed. Additional evidence of overturn is also obtained by comparing the std-GITR and sec-GITR records when available. Thus only the latter part of the records from Umbrella coracles U 1.8 and D 2.7 (Figures 3.80 and 3.88) are considered invalid because of std-GITR damage resulting from overturn. The interpretation af any dose rate record is obviously dependent upon some knowledge of visible base surge position relative to the instrument providing the record. These visible boundaries (photo-boundaries) were determined at l-minute intervals after zero time from prints of oblique aerial photographs, which were geometrically corrected for the known dis- tance and altitude of the aircraft (Section 3.3.3). The boundaries obtained cannot be more ~t Ny 119