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 cm3) coupled to 5 x 5 mm2 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.