DNA 1240H-2 (2) Gamma Radiation. Measurements of F.P.C. gamma radiation from water-surface burets were made atOperations Castle®andRedving for Gevices ranging in j ota, Tewa, and 17-5 eld | Analysis of available data from shots Flathead, Navajo permitted construction of the curves of Fig. (F.P.C. Gamma Dose ve Range for 1 MT) and the Dose Multiplying Factor, Fig.17-6. Both Figs. are redrawn from Ref. 28. Use of these two figures permits prediction of free-field F.P.C.-gamma-radiation doses from water-surface bursts of yields from 100 KT to 10 MT. Additional data are needed, however, particularly to verify the values of the dose curves atranges factor for yields greater than 12,000 ft and of the dose-mitiplying-—— ~~ ~~ t For underwater bursts, fragmentary measurements of F.P.C. gamma red- dation were made at Operations Crossroads (Baker)29, 30 and Wigwam 3! However, those measurements are not sufficiently detailed to permit re- liable predictions of gamma dose rate or gamma dose as a function of time and distance. Somewhat better measurements of F.P.C. gamma radiation were obtained at Operation Hardtack, Shots Umbrella and Wahoo 73, X, 33 The GITR data obtained indicate that the stem of the water plume pro- duced an early (less than 15-sec) significant peak gamma dose rate that fell off rapidly with distance. on Fig. 17-7, Data from Refs. 32 and 33 are plotted Several GITR'sw2e usai and the standard-GITR measurements are estimated ~ to be more reliable than those of the ASEL-GITR; how- ever all available data are plotted. It should be noted that within the first minute, significant gamma doses were measured, but the major portions of thase doses were due to transit radiation (discussed in 17.5). The F.P.C. gamma dose, estimated: 33 to have been insignificant, is plotted in Fig. 17-8. The values showm in the figures are, in general, independent of direction from burst, but because of the paucity of data, are considered reliable only within a factor of ten, and apply only to the particular test conditions. 17.4.4 Effect of Geometry on the Interaction of F.P.C. Gamma Radiation with a Target Ship No shipboard measurements have been made of F.P.C. gamma radiation from water-surface bursts. At Operation Hardtack, efforts were made to measure this radiation from underwater bursts at both exposed and shielded locations aboard target destroyers. However, no doses were recorded at the shielded locations within the first minute. The ships 17-26 EE RN meee mmr seme nere ee re ee ee ee nee eee