ENERGY RESOLUTION OF SCINTILLATION DETECTORS READOUT WITH LARGE-AREA AVALANCHE PHOTODIODES AND PHOTOMULTIPLIERS

The energy resolution of small NaI(Tl), CsI(Tl), BGO, GSO, YAP and LSO crystals has been studied using 16 mm diameter large area avalanche p hotodiodes (LAAPD) and a 52 mm diameter photomultiplier. The best resu lt of 4.8% for 662 keV gamma-rays from a Cs-137 source was obtained wi th a 9 mm in diameter by 9 mm high CsI(Tl) scintillator coupled to an LAAPD. Measuring the number of primary electron-hole pairs produced in the LAAPD and photoelectrons in the photomultiplier, as well as the n oise contribution of the LAAPD, allowed a quantitative discussion of t he results. The energy resolutions measured with LAAPDs are comparable to, or significantly better (at certain emission wavelengths) than, t hose obtained with the photomultiplier. At energies above 100 keV the energy resolution measured with the majority of crystals and the LAAPD was weakly affected by the photodiode noise contribution. The advanta ges and limitations of LAAPDs in energy spectrometry with scintillatio n detectors are also discussed.