minute at 12 hours, which had been determined by Reference 36 for fission products. and the end-window counter used to determine IC tray activities. This data suggests that the total Wahoo deposition was slightly greater than Umbrella; however, considering the assumptions required for these calculations, the differences between Wahoo and Umbrella shown by the deposit dose versus distance curves (Figures 3.32 through 3.34) are more probably due to the generally ticher backyround of the Walwo collections. 3.3.2 Free-Field Dose Rates. The free field is arbitrarily defined for the purposes of this report aS the gamma radiation field near the water surface resulting from a cloud of airborne radioactive material unmodified by any projections above that surface. The GITR records best describing the free-field dose rates are those obtained from the coracles and presented in this section (Figures 3.66 through 3.96}. Since these records are necessarily the summation of a complex sequence of interrelated phenomena, their interpretation requires considerable discussion. The corrections and modifications of both the gamma records and base surge photography with which they are compared are first described. On the basis of radiological and photographic evidence, a simple base surge model is next proposed together with some specialized terminology required for greater brevity and clarity. The general features of the two underwater detonations can then be summarized and are later substantiated by more detailed discussion. The general discussion is intended to provide an approximate description of the gross base surge phenomena suitable for estimates of tactical hazards. The detailed discussions are presented to suggest hypotheses, which may be later used as guides for a combined analysis of all final Hardtack results. The limitations and justifications for any extended treatment of the data have been stated in the introduction to this chapter (Section 3.1). Each gamma dose rate record is presented with a summary of all pertinent information considered necessary for the complete interpretation of that record. A brief synoptic description of the two underwater detonations is attempted by collecting some of this individual information into a master table (Table 3.11). All general or detailed descriptions of the records and all speculations on surge transport mechanisms are based on this material. Although the postulated base surge models and distinctions in surge structure cannot be conclusively demonstrated, they at least fit all radiological observations. Other models or structures can, of course, be postulated, andthe project places no particular emphasis on those elaborated here. Some of the material presented in this section must be abstracted from other sections of this report, since an intelligent interpretation of the free-field dose rate requires a nearly complete synthesis of all radiological observations. This material is properly abbreviated in this section; however, complete presentation of all such data is found elsewhere, viz, cloud and foam modeis are presented in Sections 1.3.1 and 1.3.2, instrument response in Section 3.1.1, isodose contours in Section 3.3.3, approach velocities and general base surge dynamics in Section 3.3.4, water- borne sources and their movement or sinking in Section 3.3.5, and shipboard records in Section 3.4.1. Reduction of surge photography was performed by the project from preliminaryprints of aerial] photographs supplied by Project 1.3, Naval Ordnance Laboratory (NOL), prior to publi- cation of Reference 91, to which the reader is referred for final reduced data. Some of these NOL radii have been incorporated into this report with the kind permission of Project 1.3 (Fig- ures 3.21 and 4.20 of Reference 91 for Wahoo and Umbrella radii, respectively). Finally, the linear presentations of dose rate which appeared in the preliminary report (ITR-—1621) are presented in Section D.1. To conserve space, only parenthetic reference to sources of additional information is made throughout the remainder of this section. Ali dose rate records obtained aboard coracles are given from zero time to H-15 minutes. a time interval that includes the major radiation phenomena associated with underwater nuclear 113 Pages 114 through 118 daleted. 93