Readout of a LaCl3(Ce3+) scintillation crystal with a large area avalanche photodiode

Large area avalanche photodiodes (APD) with high quantum efficiency and low noise figures have recently become available. In the observation of scintillation light they may replace the photo-multiplier tubes in several applications. In this paper we describe a very high resolution gamma-ray detector consisting of an 8 mm diameter and 5 mm thick LaCl₃(Ce³⁺) scintillation crystal coupled to a 16 mm diameter APD from Advanced Photonix Inc. We have measured an energy resolution of ~3.65% full-width at half maximum at the 662 keV peak of ¹³⁷Cs at room temperature. This is to our knowledge the best result obtained with a scintillation crystal coupled to a silicon detector. This was achieved taking advantage of the very low intrinsic resolution of the crystal which is assumed to be around 2%. Also the high light yield of the crystal (about 46000 photons/MeV) and the high quantum efficiency of the diode are very important