title: Identifying key surface parameters for optical photon transport in GEANT4/GATE simulations.
abstract: For a scintillator used for spectrometry, the generation, transport and detection of optical photons have a great impact on the energy spectrum resolution. A complete Monte Carlo model of a scintillator includes a coupled ionizing particle and optical photon transport, which can be simulated with the GEANT4 code. The GEANT4 surface parameters control the physics processes an optical photon undergoes when reaching the surface of a volume. In this work the impact of each surface parameter on the optical transport was studied by looking at the optical spectrum: the number of detected optical photons per ionizing source particle from a large plastic scintillator, i.e. the output signal. All simulations were performed using GATE v6.2 (GEANT4 Application for Tomographic Emission). The surface parameter finish (polished, ground, front-painted or back-painted) showed the greatest impact on the optical spectrum whereas the surface parameter σ(α), which controls the surface roughness, had a relatively small impact. It was also shown how the surface parameters reflectivity and reflectivity types (specular spike, specular lobe, Lambertian and backscatter) changed the optical spectrum depending on the probability for reflection and the combination of reflectivity types. A change in the optical spectrum will ultimately have an impact on a simulated energy spectrum. By studying the optical spectra presented in this work, a GEANT4 user can predict the shift in an optical spectrum caused be the alteration of a specific surface parameter.
authors.affiliation: The Department of Radiation Physics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Gula stråket 2B, 413 45 Göteborg, Sweden. Electronic address: jenny.nilsson@radfys.gu.se.
authors.forename: Jenny
authors.initials: J
authors.lastname: Nilsson
authors.affiliation: Institute of Nuclear Medicine, University College London Hospitals, Euston Road, London, United Kingdom.
authors.forename: Vesna
authors.initials: V
authors.lastname: Cuplov
authors.affiliation: The Department of Radiation Physics, Institute of Clinical Sciences, The Sahlgrenska Academy, University of Gothenburg, Gula stråket 2B, 413 45 Göteborg, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Isaksson
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D008027:Light; D015233:Models, Statistical; D009010:Monte Carlo Method; D017785:Photons; D011829:Radiation Dosage; D011839:Radiation, Ionizing; D011874:Radiometry / Q000379:methods*; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D012984:Software; D013499:Surface Properties
keywords: Energy resolution; GEANT4; Optical transport; Spectrometry; Surface parameters; Whole body counting