f- zetector was converted to dose rate, using such a curve specifically determined for C.3 END-WINDOW GAMMA COUNTER RESPONSE The relative response for a point gamma source on the fifth shelf of End-Window Gamma Counter 2 is given in Table C.1 and plotted in Figure C.10. Without a detailed knowledge of the energy spectra of the samples counted and without a complete analysis of distributed source effects, the energy response presented cannot be applied to the measurements obtained for the IC trays with an accuracy greater than + 30 percent. Assuming an average energy of 0.7 Mev at the time of counting, the efficiency of the End-Window Gamma Counter 2 was probably between 0.25 and 0.45 percent. C.4 FILM CALIBRATION All films used in the NBS film holders were recalibrated at EPG, using a 200-curie Co™ source. Control films were exposed over a period extending from H+1 to H+31i for Wahoo and from H—22 to H+8 hours for Umbrella, and the developmentof all film was delayed until at least H+144, to reduce possible errors due to latent image fading. The calibration curves used to interpret Wahoo and Umbrella film densities are given in Figures C.11 through C.14. All film densities were determined with an Eberline FD-2 film densitometer; however, the conversion from density to gamma dose was done manually, using the curves given. The energy response of these films in the NBS holders has been determined in Reference 121, anda summary of the results is presented in Figures C.15 and C.16. The directional response was consistent with data given in Reference 63. C.5 EMPIRICAL CORRELATION BETWEEN STD-GITR AND IC In the event of heavy deposition from the base surge, the free-field dose rate might have to be estimated from the gross gamma dose rate; the relative contribution from material deposited on coracie and detector surfaces being known. Therefore, an empirical relationship was es- tablished between a known distribution of radioactive material per unit area on the coracle surfaces, as indicated by the IC, and the resultant total field measured by the std-GITR. This conversion factor was determined by some preliminary experiments prior to departure for EPG; but, since the relative contribution from deposited material appears to be small, no detailed evaluation of the conversion factor has been attempted. Deposition from base surge was simulated by spraying a La‘ slurry over the upper section of a coracle. The technique of spraying relatively uniform deposits of radioactive material over various surfaces has been previously developed by NRDL (References 122 and 123). The project made use of the facility established at Camp Stoneman, California. The upper section of a coracle, including the instrument well and all instruments, was mounted on roller tracks so that the sensitive volume of the std-GITR detector was exactly 4.06 feet above the concrete floor (the expected distance for the detector above the ocean surface}. The scattering and al- bedo data for concrete (References 124 and 125) indicated that the backscatter from the ocean surface for 1-Mev gammas was closely approximated by the concrete floor at this distance. The coracle with its assemblage of instruments in operation was then drawn through the spray system, which deposited a known amount of La!° slurry over all coracle surfaces. The coracle was then removed from the spray area, and the resultant gammafield was measured first with the GITR in the normal coracle position and then at various distances above the coracle deck. The IC trays that collected the La’? slurry were recovered immediately and counted on Shelf 5 End-Window Gamma Counter 2, the same counter used for all subsequemt IC tray counts in EPG (Section 3.3.1). The IC tray counts, corrected for coincidence loss and decay, were used to determine the ratio between the IC counts and the GITR record (Figure'C.17). This rela-~ tionship was determined to be: Sy So “AY 367