48 THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD THEORETICAL CALCULATIONS OF THE GAMMA RADIATION SPECTRUM, ETC. 49 Decay Scheme of wl? ' ‘ Energy Relative 1) 2) 10.816 9.156 1.0 0.09 5 Jol Photon B,(Mev) Number n, Te 8.278 3) (6) (8) (9) = 15 ; \ eg 0.90 o| @ 5.287 iy 485 2.3 0.8 tit To mmBy = 468.46 Mev Ein, . -—— 6.318 5.554 (7) 0.19 1.5 En, = 7.53 4 4 5.2%, excluding cascade photons (6) and (8). + - ft 4 ct q 4 | i | 4 Figure 9.-Decay scheme of excited N*. E(Mee) Fraure 11.—Initial gamma differential dose spectrum at 1,500 yards, 2. The second point of interest is that the spectrum at 1,500 yards is harder than the spectrum at 1,000 yards: That is, its most energetic components are relatively more prominent. Previously it was shown that with moenoenergetic gamma point sources, spectra become “‘softer’’ or less energetic with increasing distance, due to the generation of secondary scattered photons of lower energy than the unattenuated source photons. Consequently, one must. conclude that with the polyencrgetic bomb source spectrum, filtration of low energy components occurs more rapidly with increasing distance in this range than does degradation of the more energetic source photons. This would give rise to a net “hardening” of the spectrum with increasing distance. At 3,000 yards the “hardening” effect of Fravre 10,—Initial gamma differential dose spectrum at 1,000 yards, increasing distance is even more apparent, ag is seen in Figure 12. In this spectrum thesingle most prominent dose contribution is made by the very most energetic constituent; namely, the 10.8 Mev gammaphotons from the nitrogen radioactive capture sources. The filtering effect of distance on the very energetic gamma spectra resulting from initial bomb gammaradiation is emphasized in Figure 13. Here there are presented simultaneously the integral dose spectra corresponding to the differential dose spectra just reviewed. [tf is seen thal with increasing distance there is a decreasing fraction of total dose contributed by photons less than-any one given energy. For example: at 1,000 yards about 73 percent of the total dose is delivered by photons of 5 Mev or less, but at 3,000 yards such photons contribute less than one-half of the total dose. In summary, this theoretical calculation of extremely hard initial gamma radiations is of