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Stochastic Radiation Transport Methods
Published in Jerry J. Battista, Introduction to Megavoltage X-Ray Dose Computation Algorithms, 2019
User-defined threshold energies for secondary photon and charged particle events force the division of labour between occasional large and routine small energy exchanges. Hard collisions by Möller or Bhabha scattering by electrons and positrons, respectively, produce particles with energies above threshold energy Ethresh = AE (Nelson et al. 1985). These knock-on particles merit follow-up as separate distinct newborn entities. Similarly, bremsstrahlung x-rays produced by inelastic scattering with transfers above the threshold energy Pthresh = AP (Nelson et al. 1985) are treated as newborn photons in analog mode. Softer charged particle collisions and bremsstrahlung x-rays dump their energy locally along the track via restricted stopping powers. This energy is deposited within a sausage-shaped region wrapped around the main particle track, while harder events give rise to energy deposited remotely from this core region. The size of this region is determined by threshold energy values. These values should be set to maintain the spatial resolution required for the problem being studied (Fippel 2013a).
Development of Chinese Female Computational Phantom Rad-Human and Its Application in Radiation Dosimetry Assessment
Published in Nuclear Technology, 2018
Yican Wu, Mengyun Cheng, Wen Wang, Jing Song, Shengpeng Yu, Pengcheng Long, Liqin Hu
Monte Carlo programs such as MCNP, EGS, and Penelope are widely used to simulate complex radiation interactions and energy depositions in the human body. In this study, the dose conversion coefficients for different energies were calculated with SuperMC, which can support neutron/photon/electron and coupled particle transport calculation. For neutrons, elastic scattering, inelastic scattering, and various absorption reaction processes including (n, xn), (n, γ), etc., are considered from 10–11 to 150 MeV. For photons, photoatomic reactions including photoelectric absorption, coherent scattering, incoherent scattering, pair production, and photonuclear reaction (γ, n) are considered. The energy range for photon transport simulation is from 1 keV to 1 GeV. For electrons, bremsstrahlung, Møller and Bhabha scattering, electron impact ionization, positron annihilation, and multiple scattering are included,28,29 and the energy range of transport simulation goes from 1 keV to 10 GeV, with the upper limit mainly determined by cross-section data. Coupled photon-electron transport simulation of SuperMC is based on the class II condensed history method. Plenty of benchmarks such as Quados (Ref. 30) and Eurados (Ref. 31) were used to validate the neutron/photon/electron and coupled particle transport calculation of SuperMC.