Development of a gamma camera based on an 8×8 array of LaBr3(Ce) scintillator pixels coupled to a 64-channel multi-anode PMT

We have developed a gamma camera based on an array of LaBr₃(Ce) scintillator pixels coupled to a multi-anode photomultiplier tube (MAPMT). It consisted of an 8times8 array of LaBr₃(Ce) pixels with a size of 5.8times5.8times15 mm3 and a 64-channel MAPMT (Hamamatsu flat-panel H8500) with an effective area of 49times49 mm². The pixels of the LaBr3(Ce) array were made from two LaBr₃(Ce) monolithic crystals with a diameter of 38 mm and a height of 38 mm, which had energy resolutions of 4.33plusmn0.02% at 356 keV and 3.25plusmn0.01% at 662 keV. They were assembled into the array with a reflector between pixels, and sealed hermetically by our own technique. The pitch of the LaBr₃(Ce) pixels, 6.1 mm, was determined to be the same as that of the anodes. The thickness of pixels was 15 mm to have moderate detection efficiency for sub-MeV/MeV gamma rays. We evaluated the performance as follows. At first, in order to remove the effect of the gain variance among anodes of the MAPMT, the array was coupled to a single-anode PMT, and collimated gamma rays from isotopes were irradiated to one pixel in the array. The energy resolutions (FWHM) were 5.4 (average) plusmn1.0 (RMS) % at 356 keV and 4.5plusmn1.0 % at 662 keV. Next, in order to obtain a gamma-ray image of 64 pixels by readout of only four channels, we used a resistor-chain readout system in the charge division method. In flood field irradiation of gamma rays, each pixel was clearly resolved. The energy resolutions (FWHM) of 64 pixels were 8.6plusmn1.0% at 356 keV and 5.8plusmn0.9 % at 662 keV. The averages were represented by (5.8plusmn0.7) (E/662 keV)^{-052 plusmn 0.02} % at energies from 122 keV to 835 keV.