Simulating gamma-ray energy resolution in scintillators due to electron–hole pair statistics

The best-possible limit to gamma-ray energy resolution in scintillators is given by the statistics of the number of electron–hole pairs produced by an incident gamma-ray, characterized by the Fano factor. The Fano factor is primarily controlled by the inelastic scattering during the electron cascade, which could be modeled by Monte Carlo simulation. Commonly used radiation transport codes do not follow the electrons to low enough energies to calculate electron–hole pair distributions. A Monte Carlo simulation for inelastic electron scattering is introduced based on cross-sections derived from data measured by Electron Energy-Loss Spectroscopy (EELS) for fast electrons. This inelastic scattering model was incorporated into the radiation transport code Penelope so that it could accurately count the number of electron–hole pairs produced by a gamma-ray. The Fano factor was calculated for the scintillators cerium fluoride (CeF3) and lutetium oxyorthosilicate (Lu2SiO5).