Multi-Pixel Photon Counter (MPPC) is a Geigermode APD developed by Hamamatsu Corp. We proposed that it could be a suitable photo-sensor for next-generation time-offlight PET detectors due to mainly its high photon detection efficiency. Therefore, we concentrated on the measurement of coincidence timing performance of various MPPCs in conjunction with LYSO crystal scintillators. With 3mm x 3mm devices of 50Jlm sub-pixels coupled to 3mm x 3mm x lOmm crystals, we have demonstrated a strong dependence of timing performance on over-voltage and temperature, and analyzed how changes in photon detection efficiency and dark counts would explain the measurements. The best coincidence timing resolution we have achieved between two identical LYSO/MPPC detectors was 240ps in FWHM. This was worse than the timing resolution of 220ps obtained with Hamamatsu H6533 fast PMT, and contradicted the expected improvement from higher photon detection efficiency. The contradiction could be explained by slow rise-time of MPPC pulse shape, transit time spread, dark counts and electronics noise from large capacitance of MPPC. In particular, the slow rise-time of MPPC pulse suggested that the need for a very low trigger threshold on the timing circuit. Since it in turn makes the detector system more sensitive to noise, this poses additional challenges for ganging multiple devices together into a commercially viable time-of-flight PET block detector. We will discuss it in detail including other challenge imposed by MPPC characteristics.
The Multi-Pixel Photon Counter (MPPC) is a Geiger-mode avalanche photo-diode (APD) developed by Hamamatsu Corp. We propose that it could be a suitable photo-sensor for next-generation time-of-flight PET detectors due to its high photon detection efficiency. We concentrate on the measurement of coincidence timing performance of various MPPCs in conjunction with LYSO crystal scintillators. With 3 mm 3 mm devices of 50 m sub-pixels coupled to 3 mm 3 mm 10 mm LYSO crystals, we have demonstrated a strong dependence of timing performance on over-voltage and temperature, and analyzed how changes in photon detection efficiency and dark counts would explain the measurements. The best coincidence timing resolution we have achieved between two identical LYSO/MPPC detectors was 240 ps in FWHM. This was worse than the timing resolution of 220 ps obtained with a Hamamatsu H6533 fast PMT, and contradicted the expected improvement from higher photon detection efficiency. The contradiction could be explained by the slow rise-time of MPPC pulse shape, transit time spread, dark counts and electronic noise from the large capacitance of the MPPC. In particular, the slow rise-time of the MPPC pulse suggests the need for a very low trigger threshold on the timing circuit. Since this makes the detector system more sensitive to noise, this poses additional challenges for ganging multiple devices together into a commercially viable time-of-flight PET block detector. We will discuss this work in detail including other challenge imposed by MPPC characteristics.
7 Pseudorapidity distributions of the two tagging jets, forward jet jet 1 and backward jet jet 2, as a function of rapidity i n tervals: Solid lines are for no rapidity boost cut and the dotted lines for rapidity boost cut.
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