Vol. 2, 2017

Original research papers

Radiation Measurements


N. Mirzajani, S. O. Souza, F. d’Errico

Pages: 59-63

DOI: 10.21175/RadProc.2017.13

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 tissue-equivalent dosimeters even with embedded OSL materials, such as CaF2, that exhibit a higher Z-value than tissue.
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