engleski

Relative efficiency of radiophotoluminescent glass detectors in low energy proton beams

In charged particle dosimetry luminescence efficiency strongly depends on linear energy transfer (LET). Therefore, for correct interpretation of the measurements in hadron radiotherapy or space dosimetry it is important to characterize the detectors efficiency as a function of LET. Unlike for other luminescent detectors, available literature data for the efficiency of radiophotoluminescent (RPL) glass detectors are scarce and especially for low energy range no data was found. The aim of this study is to evaluate relative efficiency of RPL glass detectors in low energy proton beams. RPL glasses of environmental dosimeters (silver activated phosphate glass FD-7/SC- 1 ; AGC Techno Glass Co.) with dimensions 16 x 16 x 1.5 mm2 were used in this study. Measurement of the RPL signals were carried out with the FDG-202 reader. Detectors were exposed to proton beams in a high vacuum chamber at the microprobe experimental line of the RBI accelerator facility. A focused proton beams (1 x 1 mm2) were delivered using two electrostatic tandem accelerators: 1 MV and 6 MV accelerator for up to 2 MeV and 3-5 MeV proton beams, respectively. In all cases protons were stopped in the detectors. The range and LET of protons in water and RPL glass were calculated using SRIM code and used for absorbed dose calculations. Detectors were exposed to protons at the fluence range of 3.3x10^6 to 1.3x10^8 p/mm2 while doses absorbed in the irradiated volume, expressed as dose to water, ranged from 7.6 to 797.8 Gy. Firstly, fluence/dose response was investigated [1]. Secondly, RPL signals from the linear dose response range were used to evaluate efficiency relative to reference gamma radiation. Preliminary results show that in the linear fluence/dose response range the mean RPL signal normalized to the number of incident protons is decreasing exponentially with decrease of the beam energy. The relative efficiency (expressed for dose in water, relative to 60Co) is also decreasing with energy/LET from 0.6 for 5 MeV (8.1 keV/m) and 0.2 for 3 MeV (12.1 keV/m) to approximately 0.1 for 2 MeV and below.

radiophotoluminescent detectors ; relative efficiency ; proton dosimetry

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