  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 70keV 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.
