THEORETICAL CALCULATIONS OF THE GAMMA RADIATION SPECTRUM FROMINITIAL AND FALLOUT RADIATIONS OF NUCLEAR WEAPONS By D. C. Borq Brookhaven National Laboratory INTRODUCTORY REMARKS In another paper to be presented by Dr. Bond later at this conference emphasis will be given to the dependence of whole-body radiation effects upon depth dose factors. Since penetration of ionizing radiations into targets depends upon the energy of the incident photons as well as upon the geometry of exposure, development of spectral information concerning fallout gam- ma radiations becomes highly pertinent to the calculation of biological responses ta be expected from fallout gammafields. However, questions may well be raised as to the pertinence of discussing initial gammaradiation spectra at a conference on fallout. In answer to this several considerations may be cited, to wit: The same theoretical treatments apply to both initial and fallout geometries, so support for the former case by relatively good data increases the validity of conclusions and in- sights derived from the application of a com~panion approach to the latter geometry. In actual fact the constancy and certainty of the input data for the initial gamma radiation case are far superior to those for the fallout gamma case. Furthermore, actual field meas- urements of garoma air dose correlated with weapon parameters are vastly more accurate and more numerous for initial bomb gamme radiations than for fallout gammas. In short, the theoretical treatment that can give insight into aspects of fallout gammeradia- tions can best be checked experimentally for theinitial bomb gammaradiation case. Moreover, a parallel situation exists with respect to radiation damage criteria for man: namely, that the data correlated with initial bombradiations and their laboratory counterparts are far more numerous and better documented than are those for fallout radiations. Thus, there is practical radiobiological significance in understanding the mechanismsof initial bomb radiations: so that the radiobiclogical dose-response criteria derived from them will be properly adjusted for application to fallout radiations or to other conditions. This concept is generalized and developed more corpletely in Dr. Bond’s companion paper. THEORETICAL METHOD The general nature of the theoretica] method applied to bomb gamme. radiations in this paper may be summarized briefly. Gemma ray propagation in an infinite medium can be defined by 8 partial linear integrodifferential equation—thatis, a so-called “transport equation,” [1, 2, 3]. This equation considers all the major interaction processes be- tween gamma, photons and the medium: namely, photoelectric absorption, Compton interactions with associated generation of secondary photons with their altered angular distributions, and positron-electron pair production, The equetion that represents this can account for the 89