Project 2.1 (Reference 9). However, there is still some uncertainty on this point, and the curves presented may be off in absolute magnitude, although the shape of the curves as a function of time is probably correct. The initial-gamma values given represent those observed at the detector and should be multiplied by a factor of approximately 1.2 to correct for station shielding. This factor of 1.2 is a measured value of the attenuation of the blast shield for Co® radiation; the attenuation is a function of the energy of the incident radiation. Time is a factor only in that after one minute there is litthe gamma radiation in this energy range (>1 Mev). Figures 3.23 through 3.28 should be multiplied by 1.2 to give free-field values. The data in Figure 3.26 is in reasonable agreement with similar cata in Reference 9, especially after the data of Figure 3.26 has been extrapolated to a time equivalent to that reported by Operation Redwing Project 2.1. Figures 3.27 and 3.28 show that approximately "h; ot the total-initial exposure for Shot Flathead 221.04 and Shot Navajo 221.05 was delivered after the arrival of the shock front. Most of this exposure was due to the ewhancement caused by the hydrodynamic effect because the exposure rate was decuying rapidly before the arrival] of the shock front. Reference 9 compares measured-initial-zanima exposure -versus-distance curves with curves computed from TM 23-200. For the purpcse of comparison with published data, integrated-initial-gamma-rate datu from Figures 3.26, 3.27, and 3.28 of this report have been plotted cn the corresponding curves trom Keference 9. In addition, extrapolation of Project 2.2 measuved data (integrated-initial-gamma rate) to include initial-gamma dose delivered ufter the end of project records has been made using information and methods in Reference 10. Exposure received prior to stari of project records has been neglected, since the e.posure vas relatively insignificant. The abovementioned plots for Shot Zuni are vncwn in Figure 3.29 und for Shots Flathead and Navajo in Figure 3.30. 3.3 BEACH-BALL MEASUREMENTS The objective of measuring the exposure rute at the lip of the crater from Shot Zuni was assumed by Project 2.2 at a late stuye on the preparations for Operation Redwing. The beach-ball instrument was dropped ontu the Shot Zuni cra'ter lip at H + 6 hours. The fall apparently caused a change in the calibration of the system, because the received data indicated an exposure rate as high as 40,Cu0 r/hr at this late time. Further- “more, rotor interference mace reception of the transmitted signal aifficult. 3.4 THERMAL-RADIATION DETECTOR The thermal-radiation detectur @us installed on S'te Nan for Shot Tewa at a range of approximately 20 miles, and the detonation was satisfactorily detected. 49