62 THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD 80. THEORETICAL CALCULATIONS OF THE GAMMA RADIATION SPECTRUM, BIC. 63 30 creme ORIGINAL SOURCE SPECTRUM rr ORIGINAL SOURCE SPECTRUM 0 INFINITE PLANE 3IN ASR L ' , , Le 200 6 ” 3 n ° T 6 6 commen PER CENT OF TOTAL OOSE PER CENT OF TOTAL OOSE comewm INFINITE PLANE, 3IN AIR 4 1 aco 1 600 L 600 1000. ENERGY (KEV) i 1500 600 4, 1 @00 1000 ENERGY [KEV 100 Figure 23.-—-Disiribution of inherent energies of gamma radiation from an actual mixed fission product sample and histogramof degraded energies calculated for 3 feet in air above a uniformly distributed fission products field, COMPARISON OF INITIAL AND FALLOUT GAMMA SPECTRA In conclusion it may be said that the theo- retical calculations of initial and fallout gamma spectra and dose appear reasonably well supported by known data. In this regard it then becomes of interest to review and compare representative spectra calculated for initial and fallout gamma radiations. Figure 24 shows again the fallout spectrum of Figure 23, this time in conjunction with an initial gamma spectrum at 1,500 yards from a typical relatively low yield weapon, which was presented earlier in Figure 11. Noting the different expansions of the energy scales along the abscissnas for the two cases presented here, it is apparent that although the fallout spectrum might be said to be a “hard” one, the initial gemma spectrum is still vastly more energetic, CONCLUSIONS AND SUMMARY 1. A theoretical method for describing the propagation of gamma rays in various media has been developed, and numerical solutions have been carried out to the point where total dose and 4x-volume spectral calculations can be made. Further computer calculations could make available spectral information as a function of angular distribution, and this might be desired for shielding studies. a. The method has been normalized to weapons parameters for the case of initial bomb gammaradiation, and resultant doseversus-distance predictions’ generally fit in well with observed field data. 6. Although application to the fallout case is more empirical, the compatibility of the calculations with what data are available and the general validation of the underlying theory and application in the initial gamma Eftow) Fraure 24.—Comparison of differential gamma dose spectra for initial and fallout radiation (Figs. 11 and 2$).