Incorporation of Monte Carlo Electron Interface Studies into Photon General Cavity Theory

Electron Monte Carlo calculations using CYLTRAN and a new PHSECE (Photon-Produced Secondary Electrons) technique were carried out to estimate electron fluences and energy deposition profiles near LiF/Al and LiF/Pb material interfaces undergoing ⁶⁰Co gamma irradiation. Several interesting and new features emerge: (a) although the buildup of the secondary electron fluences at the interfaces of the irradiated media is approximately exponential, the value of the electron mass fluence buildup coefficient, γ, is not equal to the electron mass fluence attenuation coefficient, β;(b) the β value of the attenuation of the gamma generated electron fluences at the cavity/medium interfaces is strongly dependent on the Z of the adjacent material; and (c) for LiF/Pb there is a significant “intrusion” energy deposition mode arising from sidescattering in the wall material (lead). These new features of interface dosimetry (at least items a and b) are incorporated into the photon general cavity expressions of Burlin (as modified by Horowitz, Dubi, and Moscovitch) and Kearsley and compared with experimental data.