Validation of the Geant4 simulation of bremsstrahlung from thick targets below 3 MeV

Abstract

The bremsstrahlung spectra produced by electrons impinging on thick targets are simulated using the Geant4 Monte Carlo toolkit. Simulations are validated against experimental data available in literature for a range of energy between 0.5 and 2.8 MeV for Al and Fe targets and for a value of energy of 70 keV for Al, Ag, W and Pb targets. All three independent sets of electromagnetic models available in Geant4 to simulate bremsstrahlung are tested. A quantitative analysis is performed reproducing with each model the energy spectrum for the different configurations of emission angles, energies and targets. At higher energies (0.5-2.8 MeV) of the impinging electrons on Al and Fe targets, Geant4 is able to reproduce the spectral shapes and the integral photon emission in the forward direction. The agreement is within 10-30%, depending on energy, emission angle and target material. The physics model based on the Penelope Monte Carlo code is in slightly better agreement with the measured data than the other two. However, all models over-estimate the photon emission in the backward hemisphere. For the lower energy study (70 keV), which includes higher-Z targets, all models systematically under-estimate the total photon yield, while still providing a reasonable agreement between 10 and 50%. The results of this work are of potential interest for medical physics applications, where knowledge of the energy spectra and angular distributions of photons is needed for accurate dose calculations with Monte Carlo and other fluence-based methods.

Predicting the particle-induced background for future x-ray astronomy missions: the importance of experimental validation for GEANT4 simulations

“…Comprehensive validation of fundamental physical processes such as bremsstrahlung production 22 , electron energy deposition 23 , electron backscattering 24 and PIXE 25 have been performed, and GEANT4 itself undergoes an extensive validation procedure after each update 26 . The majority of these validation efforts focus on energy ranges beyond those relevant to the background simulations of this paper, and as such the error introduced by GEANT4 to the background estimates is not well understood.…”

Progress in Geant4 Electromagnetic Physics Modelling and Validation

“…The three bremsstrahlung models available in Geant4 which are applicable in the low-energy range (Standard_Option3, Livermore and Penelope) were recently compared against experimental data below 3 MeV in thick target experiments [14]. Data between 0.5 and 2.8 MeV on Al and Fe targets, which include absolute single and double differential bremsstrahlung yields, were taken from [15].…”

“…At least 10 9 events were generated for each target/energy configuration. A few examples of double-differential distributions of the photon yield (in angle and energy) are displayed in [14].…”

Recent Developments in Geant4

“…A specific EM validation suite [133] runs on a regular basis for each reference version of GEANT4 (see [34,57,73] and references therein). Dedicated validations of cross sections, stopping powers, and atomic transition energies versus evaluated data and theory are done by GEANT4 developers and different user groups (see, for example, [35,134,135] and Fig. 11).…”