Interface dosimetry: measurements and Monte Carlo simulations of low-energy photon beams

A comparison of measured and simulated dose perturbations at high-Z interfaces with Monte Carlo (MC) codes, EGS4, MCNP4B, and PENELOPE, having varied algorithms is presented. The measured dose perturbations strongly depend on the chamber design and are always lower than the MC data. The EGS4 data are closer to the ion chamber values. The other two codes, MCNP4B and PENELOPE, predict relatively higher magnitude. The simulated secondary electron spectra from high-Z interfaces are different but cannot explain the differences in magnitude. It is concluded that MC codes capable of handling low-energy transport and better boundary crossing algorithms are needed for interface effects. (C) 2001 Elsevier Science Ltd. All rights reserved.