Monte Carlo Simulations of Thin Films Loaded With Osl Detectors

Abstract

Abstract. The transport and interactions of gamma-rays in a thin film loaded with optically stimulated luminescence (OSL) nanoparticles (NPs) were studied by Monte Carlo (MC) simulations with the Particle and Heavy Ion Transport code System (PHITS). In the MC input file, the geometry of the thin film was treated as a virtual space using a cubic voxel structure with a lattice of nanoparticles (NPs) of OSL CaF2:Ce. The particles were monodispersed, ranging in size from 50 to 600 nm. The polyvinyl chloride (PVC) film matrix was treated as an array simulating a small sample with an area of 13.8 µm by 13.8 µm and a thickness of 10.2 µm. For the irradiation simulations, we considered a collimated beam of cesium-137 gamma-rays of 662 keV impinging perpendicularly on the piece of thin film (detector). The film was centered on the front face of 30 cm x 30 cm x 15 cm ISO water slab phantom. In the MC simulations, we followed the radiation tracks and calculated the energy deposition from the tracks of electrons produced by the interaction histories of the photons crossing the thin film. The energy deposition in the OSL film is initially fairly constant with grain size and then increases as the CaF2:Ce grains get larger to the point of filling 50% of the voxel volume. For grain sizes up to almost 400 nm, the presence of the grains has minimal impact, i.e., the dose is mainly deposited by secondary electrons generated within the polymer. This allows for the design of tissueequivalent dosimeters even with embedded OSL materials, such as CaF2, that exhibit a higher Z-value than tissue.

New optically stimulated luminescence dosimetry film optimized for energy dependence guided by Monte Carlo simulations

“…By reducing the grain size from 3 μm to 230 nm we were able to reduce the energy dependence by almost 50%. This is in line with the cavity theory and previous study from Mirzajana, et al, demonstrating the advantage of reducing the grain size on the photon energy response (Mirzajani et al 2017). An in-depth study of the energy deposition and energy transfer from electrons generated in and around 50 or 100 nm gold nanoparticles (GNP), irradiated with x-rays, has been recently published (Rabus et al 2021).…”

“…In recent works, TE optimization of OSL films was carried out using three-dimensional MC simulations of films containing dispersed luminescent micro or nanoparticles of CaF 2 :Ce (Mirzajani et al 2017). A voxel phantom model was created for different grain diameters, varying from 50 to 600 nm, and tested with Cs-137 (662 keV), which demonstrated the advantage of reducing the grain sizes on the photon energy response.…”