Monte Carlo Calculations of Electron Fluence Attenuation Coefficients for Photon General Cavity Theory

Abstract

Application of photon general cavity theory requires knowledge of the electron mass attenuation coefficient, ß. One approach has been to adopt values of ß derived from the attenuation of beta ray spectra, which are based on a one-to-one correspondence between ß and the maximum energy of the beta ray spectrum. Other approaches are also available, so that, for 60Co generated electrons, for example, six different empirical expressions yield values of ß for LiF from a minimum value of 5.16 cm2.g-1 to a maximum value of 14.26 cm2.g-1. The results are reported of coupled photoelectron Monte Carlo calculations over a wide range of photon energies, 0.1 MeV < E < 1.4 MeV, and wall materials; Al, Cu, Cd and Pb. For the relatively low Z materials and over the energy range 0.3 MeV to 1.4 MeV, ß in LiF is given to within an accuracy of ±10% by the relation ß = 10.5 E-1.82 where E is expressed in MeV. ß is strongly dependent on Z so that for the high Z materials a simple power law relationship does not exist for any extended range of gamma ray energies.