Evaluation of the energy resolution of a prompt gamma-ray imaging detector using LaBr3(Ce) scintillator and 8 × 8 array MPPC for an animal study of BNCT

To develop boron neutron capture therapy (BNCT), it is desired to measure 10B concentration and obtain a two-dimensional 10B distribution in animal studies. In this research, we develop a prompt gamma-ray imaging detector to measure 10B distribution using a 50 mm × 50 mm x 10 mm LaBr3(Ce) scintillator and a multi-pixel photon counter (MPPC). To measure a two-dimensional 10B distribution, the 478 keV gamma-ray emitted from 10B(n,α)7Li reaction should be measured with the discrimination from 511 keV background gamma rays in each MPPC. Furthermore, as a characteristic of the detector, it is necessary to investigate whether the 478 keV events individually incident on the MPPC can be measured in two dimensions. In this study, we evaluated the energy resolution and performed a two-dimensional distribution measurement using a thermal neutron beam and prompt gamma rays from a boron sample. This system was able to obtain energy resolution as full width at half maximum at 511 keV of 5.0 ± 0.2% in all MPPC pixels, better than the 6.5% energy resolution required to discriminate between 478 and 511 keV gamma rays. When the region of interest (ROI) was set up from -3σ to – σ (first ROI) and -3σ to the median (second ROI) for the Gaussian distribution of a 478 keV gamma-ray peak using a 6.25 ppm sample, the detector count rate of the 478 keV gamma rays was 0.03 and 0.11 cps, respectively, without a collimator. Moreover, the effect due to the overlapping 511 keV gamma ray peak was approximately 2.0% in the first ROI and approximately 3.2% in the second ROI. In addition, the counts of 478 keV gamma rays were visualized in two-dimensional. •A prompt gamma-ray imaging detector was developed with a LaBr3(Ce) scintillator and a multi-pixel photon counter (MPPC).•This system was able to obtain energy resolution as full width at half maximum (FWHM) at 511 keV of 5.0 ± 0.2% .•It was confirmed that this system could discriminate 511 keV gamma rays as background and 478 keV prompt gamma rays.•The two-dimensional counts distribution of 478 keV gamma rays from 50 ppm sample was measured.