Evaluation of bremsstrahlung contribution to photon transport in coupled photon–electron problems

• Published in: Radiation physics and chemistry (Oxford, England : 1993) Vol. 116; pp. 203 - 207
• Main Authors: Fernández, Jorge E., Scot, Viviana, Di Giulio, Eugenio, Salvat, Francesc
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2015
• Subjects: Bremsstrahlung; Computer simulation; Deterministic transport; Joining; Mathematical models; Monte Carlo methods; Monte Carlo simulation; Photons; Photon–electron transport; Transport; X-ray spectrum; Photon–electron transport; Bremsstrahlung; X-ray spectrum; Monte Carlo simulation; Deterministic transport
• ISSN: 0969-806X; 1879-0895
• DOI: 10.1016/j.radphyschem.2015.05.026

The most accurate description of the radiation field in x-ray spectrometry requires the modeling of coupled photon–electron transport. Compton scattering and the photoelectric effect actually produce electrons as secondary particles which contribute to the photon field through conversion mechanisms like bremsstrahlung (which produces a continuous photon energy spectrum) and inner-shell impact ionization (ISII) (which gives characteristic lines). The solution of the coupled problem is time consuming because the electrons interact continuously and therefore, the number of electron collisions to be considered is always very high. This complex problem is frequently simplified by neglecting the contributions of the secondary electrons. Recent works (Fernández et al., 2013; Fernández et al., 2014) have shown the possibility to include a separately computed coupled photon–electron contribution like ISII in a photon calculation for improving such a crude approximation while preserving the speed of the pure photon transport model. By means of a similar approach and the Monte Carlo code PENELOPE (coupled photon–electron Monte Carlo), the bremsstrahlung contribution is characterized in this work. The angular distribution of the photons due to bremsstrahlung can be safely considered as isotropic, with the point of emission located at the same place of the photon collision. A new photon kernel describing the bremsstrahlung contribution is introduced: it can be included in photon transport codes (deterministic or Monte Carlo) with a minimal effort. A data library to describe the energy dependence of the bremsstrahlung emission has been generated for all elements Z=1–92 in the energy range 1–150keV. The bremsstrahlung energy distribution for an arbitrary energy is obtained by interpolating in the database. A comparison between a PENELOPE direct simulation and the interpolated distribution using the data base shows an almost perfect agreement. The use of the data base increases the calculation speed by several magnitude orders. •The MC code PENELOPE is used to compute the bremsstrahlung from secondary electrons.•A library database comprising the bremsstrahlung energy distribution is built.•It is developed a new photon kernel describing the bremsstrahlung contribution.•The new kernel can be easily used in any photon transport code.•The use of the data library improves the computational speed by 5 magnitude orders.