Development of an 8x8 array of LaBr3(Ce) scintillator pixels for a gaseous Compton gamma-ray camera

We have developed LaBr3(Ce) pixel scintillator arrays for an electron-tracking Compton camera (ETCC) that consists of a gaseous time projection chamber (TPC) and the scintillators. The TPC measures the three-dimensional track and energy of a Compton recoil electron, while the scintillators measure the energy and position of the scattered gamma ray. Therefore, the ETCC is able to reconstruct Compton scattering event by event. We adopted LaBr3(Ce) scintillators because the angular resolution of the ETCC depends on the energy resolution of the scintillators, and LaBr3(Ce) has an FWHM energy resolution of about 3% at 662 keV using a single-anode photomultiplier tube (PMT). We have developed an 8x8 array of LaBr3(Ce) scintillator pixels with a pixel size of 5.8x5.8x15.0 mm3, which has an FWHM energy resolution of 5.8±0.9% at 662 keV when coupled to a multi-anode PMT (Hamamatsu H8500). The ETCC with the LaBr3(Ce) arrays has an FWHM angular resolution of 4.2±0.30 at 662 keV.