Detection of antihydrogen annihilations with a cryogenic pure-CsI crystal detector

In the framework of the ATHENA experiment a combined tracking and photon detector, operating close to liquid nitrogen temperatures, was developed to determine simultaneously the vertex of an antiproton annihilation and energy and direction of photons stemming from a positron annihilation. The photon detector consists of 192 pure-CsI scintillation crystals (≈4 cm 3 ) coupled to 5×5 mm 2 avalanche photo-diodes, which are read by electronic chips realised in VLSI CMOS technology. These read out chips are also operational at liquid nitrogen temperature and feature a self-triggering capability.