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Evaluation of the multi-pixel photon counters with inorganic scintillators

Multi-Pixel Photon Counter (MPPC) is a Hamamatsu's new Si avalanche photodiode. The main features of the MPPC are very high gain (105 to106) and very fast operation. The MPPC offers considerable advantages over widely used photomultiplier tubes (PMT) for scintillation detection, especially due to their high quantum efficiency, low cost, compactness, low operating voltage, mechanical robustness and insensitivity to magnetic fields. One of the most attractive applications of MPPCs is positron emission tomography (PET). In the present study, the MPPCs were coupled to inorganic scintillators including LSO, BGO and YAP in order to evaluate the scintillator/MPPC devices in terms of energy and timing resolutions for PET applications. The scintillation detector consisted of an LSO scintillator (2 mm × 2 mm × 4 mm) coupled to an MPPC exhibited energy resolutions of 196 keV FWHM and 189 keV FWHM for 511 keV and 662 keV gamma-rays, respectively. The MPPC was operated at a bias of 71.4 V and at room temperature. In order to investigate timing properties of the LSO/MPPC device, coincidence timing spectra between a reference scintillation detector which consisted of a BaF2 crystal coupled to a PMT and the LSO/MPPC device were measured with 511 keV positron annihilation gamma-rays from a 22Na source. A coincidence timing resolution of 3.2 ns FWHM was obtained with the LSO/MPPC system.