Reliability of high quantum efficiency MA-PMT for spectrometric quality assurance of scintillation imagers

The outstanding semiconductor photodetectors with high quantum efficiency have interested the scientific community for their potential of assembling a new class of scintillation imagers with very high energy and spatial resolution performances at low cost. Recently we assisted also to a strong technological advance in Photo Multiplier Tube (PMT) by increasing of photocathode Quantum Efficiency (QE) up to 42% peak value. From a pragmatic point of view the aim of this work is to test if this technology is ready for imaging applications and mainly focused on the investigation of energy resolution and pulse height linearity performances. Two Multi Anode PMTs (MA-PMT) were tested: a standard Hamamatsu H8500 and a new modified one, equipped with SuperBiAlkali (SBA) photocathode, with enhanced QE. The PMTs were coupled to a LaBr₃(Ce) continuous crystal dedicated for imaging application. The MA-PMT responses were tested utilizing two electronic chains: one dedicated for spectroscopy, where the 64 PMT outputs were reduced to only one signal, and a second one, utilizing 64 channels readout for imaging. These MA-PMTs have shown very good linearity response, up to 1 MeV photon energy, and high performances in term of energy resolution, demonstrating that this technology is particularly indicated to develop imaging devices with enhanced spectroscopic response.