Development of APD readout for pure-CsI crystals at cryogenic temperatures

To detect 511 keV γ-rays from positron annihilations, a detector with 192 pure-CsI crystals and APD readout was developed to determine the energy and direction of the two back-to-back γ-rays. The working temperature of the detector is ∼140 K. The performance of crystal and APD at cryogenic temperatures are described.