is assumed. All initial dose rate data is summarized in Table 3.4. The variation tn the time of ‘al peak is probably due to errors in determining true zero time on individual GITR re Tc 48, the initial peak dose rates for Umbrella are plotted without decay correction. "the initial dose rate peaks for Wahooin the average time of the imtial peaks \o.3 Seconds) has been corrected to the average time of the Umbrella peaks (1.6 seconds) using a decay curve recently determined (Section B.2 and Reference 87). Unfortunately, the station density is too low to permit any conclusions; however, the following observations can be made: (1) a period of low radiation intensity definitely follows an initial dose rate peak that appears to be associated with the surfacing of the explosion bubble, and (2) there is the suggestion that this initial radiation was registered at greater distances during Umbrella. The single Wahoo station between radial distances of 4,600 to 6,000 feet did not register an initial dose rate peak, whereas three out of three stations in this same range of distances registered such a peak during Umbrella. The existence of a period of low radiation intensity after the initial dose rate peak poses some difficult questions. The decline in dose rate immediately after the initial peak is too abrupt to be caused solely by decay and therefore implies some sort of shielding between the source and the detector. Rough calculations indicate that the amount of water comprising the plumes and column cannot afford sufficient shielding to produce the observed effects. Therefore some physical action that accomplishes the temporary submergence of the principal radiating source below the ocean surface appears to be required. Further speculation is left to those more familiar with the hydrodynamics of these events. Because of the extremely short duration of the initial radiation, little can be inferred concerning the true initial dose or the shape of the initial dose rate peak. The data obtained from the coracles strongly suggests that the true peak is much sharper than that reconstructed by Project 2.1 (Reference 86); their data is, however, the best available until more precise measurements can be made. The second portion of the early gamma record is the dose due to shine (Appendix F) from the column and approaching base surge. Photographic evidence (Reference 88) indicates that for Wahoo the primary plumes reached maximum height at 15.5 seconds (maximum height of secondary plumes at 30.5 seconds), and the base surge was clearly distinguishable by about 25 seconds; for Umbrella the column reached its average maximum height at 15 seconds,. and the base surge was clearly distinguishable at about 13 seconds. On both shots a steep rise in dose rate occurs before the time of base surge emergence established by photographs. This first steep rise may also be associated with the initial surfacing of the explosion bubble. For Wahoo it is more pronounced ind is usually followed by a short plateau, which is terminated at about the time of base surge emergence by a more gradual increase in dose rate. For Um- brella it is evident only as a change in slope, which again corresponds roughly to base surge emergence. Using the times of arrival (TOA) defined in Section 3.3.4, the cumulative dose from zero time to TOA has been calculated as an estimate of the shine dose. For greater convenience, the cumulative dose due to initial radiation, shine and the total dose to 1 minute are presented in Table 3.5. Because of its short duration, the initial radiation dose must also be regarded as an estimate. This initial dose is considered too uncertain to justify the construc- tion of isodose contours. 3.3. Contours of cumulative dose at 1 minute may be found in Section 3.3.3. GAMMA RADIATION FIELDS RESULTING FROM AIRBORNE RADIOACTIVE MATERIAL As stated in the introduction of this report, radiation from the airborne radioactive material may be divided into radiation from (1) the base surge, (2) the column and transiting cloud, and (3) material deposited from either of these two sources. The deposited material may be further subdivided into that deposited on retentive surfaces and that deposited in the ocean where mixing can occur. Radiation fields resulting from the airborne radioactive material specifically exclude those due to waterborne radioactive material, shine from the column, and secondary fallout, which is improbable in the case of an underwater burst. The two latter sources did not 89 (Text continued on Page 105) Pages 90 through 104 deleted.