60 THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD THEORETICAL CALCULATIONS OF THE GAMMA RADIATION SPECTRUM, ETC. 1.00 Lon energy with cum source delivered photons leas than Dy 3,8) = Curve A = Fraction of energy Ey. scattered from source by ive red SOURCE ENERGY &; (Mev) Fiaune 21,—Plane isotropic source, interpolation curves for elevation of $ feet above the plane. not only the intensity of fallout at a given location, but also the fractionation and partition of fission product source activities within the fallout. Moreover, even for a given set of weepon, surface, and meterological conditions—in fact, even after all fallout actually has been deposited Inthis figure the dashed bars represent the original source spectrum analyzed from a4 fallout. sample on the fourth day after the detonation. The histogram spectrum was then constructed following the methods discussed here, This dose spectrum is relatively “hard’’ or energetic compared with most laboratory in @ given instance, the nature of the fission sources, but it is not nearly so energetic as the This will result from both the natural decay gammaradiations. product gamma source will change with time. scheme of fission products and from leaching and weathering processes. Despite these uncertainties in the prediction of fallout gamma sources, some representative picture of fallout gamma spectra may be drawn by applying interpolation curves for plane source geometries to fallout sample sources analyzed in actual field experiences, This has been done by Sondhaus[8] for a fallout sample obtained following the “Bravo” event of Operation CASTLE,as is seen in Figure 23. azo dose spectra previously presented for the initial Although this spectrumis generally compatible with dose spectra actually surveyed in comparable fallout fields, even further support might be given to the analytical method if attempts were made to correlate computer- calculated predicted total gamma dose above analyzed fallout fields with actual measured data. This would be similar to the test employed in the initial gamma case, but to date apparently it has not been attempted. 2 3 4 ENERGY (Mev) Fioure 22.-Sample plane isotropic source, integral dose spectrum, 3 feet above the plane. 61