New frontiers of radiation detectors using large-area MPPC arrays

MPPC, also known as Silicon Photo-Multiplier (SiPM) is a compact high performance semiconductor photodetector consisting of multiple Geiger-mode APD pixels. The MPPC has many advantages, such as insensitivity to magnetic fields, effective time resolution and compactness. In addition, it is operated in Geiger-mode, meaning its gain may be almost comparable to that of PMTs at up to the 10⁶ level. Recently, various types of large-area monolithic MPPC-arrays are being developed and implemented in the radiation detectors hence replacing traditional PMTs in a number of applications. In this paper, I first review the basic properties of MPPCs against conventional APDs (of a typical gain up to ∼100) to attract its merits as a photodetector. Next, high spatial resolution gamma-ray imagers utilizing MPPC-arrays were fabricated with various sub-millimeter scintillation crystals. I will report on a prototype gantry for future MPPC-PET scanner, including MRI, TOF and DOI technologies. Finally, I will briefly introduce a novel Compton camera weighting only 1.9 kg and measuring just 13 x 14 x 16 cm³ in size. Despite its compactness, the camera realizes a wide 180deg field of vision with a sensitivity ∼1% for 662 keV gamma rays, with an angular resolution Δθ ∼10deg. (author)