Monte Carlo Analysis of Dose Profiles near Photon Irradiated Material Interfaces

Dose profiles in silicon and polyethylene next to gold-silicon and gold-polyethylene interfaces, due to x-rays of energies between 10 and 2000 keV, have been calculated using the POEM Monte Carlo electron transport code. By calculating separately the transport of Compton, K-, M-and L-photoelectric, and Auger electrons generated in the gold, each contribution to the total energy fluence profile was obtained and fit to the functional form A exp (Bx+Cx2+Dx3). Differentiating this form and summing over all source contributions led to excellent analytic representations of the dose profile next to gold for energies below 200 keV. Above 200 keV the dose profiles for two directions of photon irradiation were obtained by the method of Chadsey. Curves of relative dose and relative mean dose as a function of x-ray energy for several distances from the interface were calculated for the first time.