Properties of avalanche photodiodes for applications in high energy physics, astrophysics and medical imaging

Avalanche Photodiodes (APDs) with reverse structure and very good sensitivity to visible light are the first time used in large scale for the readout of PbWO4 crystals in the barrel of the CMS electromagnetic calorimeter. They have to operate in a rather hostile environment, in a magnetic field of 4 T and under unprecedented radiation levels for a minimum of 10 years with a failure rate substantially lower than 1%. After an extensive R&D work the mass production started recently. The properties of the APDs and the possibilities for modifications of some parameters for other applications will be discussed. Particularly interesting is the status of APD arrays and the prospects of their development for PET scanners and for X-ray imaging.