Abstract
After a summary description of the theory of elastic collisions of nucleons with atoms, we present the calculation of a generic database of differential and integrated cross sections for the simulation of multiple elastic collisions of protons and neutrons with kinetic energies larger than 100 keV. The relativistic plane-wave Born approximation, with binding and Coulomb-deflection corrections, has been used to calculate a database of proton-impact ionization of K-shell and L-, M-, and N-subshells of neutral atoms These databases cover the whole energy range of interest for all the elements in the periodic system, from hydrogen to einsteinium (Z = 1–99); they are provided as part of the penh distribution package. The Monte Carlo code system penh for the simulation of coupled electron-photon-proton transport is extended to account for the effect of the transport of neutrons (released in proton-induced nuclear reactions) in calculations of dose distributions from proton beams. A simplified description of neutron transport, in which neutron-induced nuclear reactions are described as a fractionally absorbing process, is shown to give simulated depth-dose distributions in good agreement with those generated by the Geant4 code. The proton-impact ionization database, combined with the description of atomic relaxation data and electron transport in penelope, allows the simulation of proton-induced x-ray emission spectra from targets with complex geometries.
Highlights
Motivated by the specific needs of protontherapy and proton-induced x-ray emission, we have recently extended the PENELOPE code system [1] to introduce the simulation of interactions and transport of protons [2, 3]
Elastic collisions of protons with nuclei are described by Collisions of Nucleons with Atoms means of numerical differential cross sections (DCSs) obtained as the product of the DCS for scattering by the bare nucleus, which was computed by the method of partial-waves with the global optical-model potential of Koning and Delaroche [4], and a screening factor accounting for the effect of the screening of the Coulomb field of the nucleus by the atomic electrons, which was calculated from the eikonal approximation for the Dirac-Hartree-Fock-Slater potential of neutral atoms [2, 3, 5]
Proton-induced electronic excitations are simulated by means of DCSs obtained from the Born approximation with the Sternheimer-Liljequist model of the generalized oscillator strength (GOS) [1], which is modified by rescaling the relative contributions of the various electron subshells to give cross sections for the impact ionization of inner subshells equal to unpublished results obtained from accurate atomic GOSs [2]
Summary
Motivated by the specific needs of protontherapy and proton-induced x-ray emission, we have recently extended the PENELOPE code system [1] to introduce the simulation of interactions and transport of protons [2, 3]. We present the theory and computational aspects of the calculation of the DCSs for elastic collisions of neutrons and protons, and of the cross sections for ionization of inner electron subshells of atoms by proton impact. We present a simplified algorithm for the simulation of the effect of neutron transport in Monte Carlo calculations of dose distributions from proton beams, which only uses the information provided in the calculated elastic-scattering database, that is, the total and DCS for elastic collisions and the reaction cross section, which is one of the basic parameters used to set the nuclear optical-model potential.
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