Single photon Si detectors were fabricated by STMicroelectronics and fully characterized in standard operation conditions and after irradiations. Both single cells and arrays, of dimensions ranging from 5x5 up to 64x64, were electrically tested. The devices operation was studied as a function of the temperature from -25°C to 65°C varying the voltage over breakdown, from 5% up to 20% of the breakdown voltage before and after irradiation using both light ions, 10 MeV B ions to doses in the range 3×107 - 5×1010 cm-2, and X-rays irradiations in the range 0.5 - 20 krad(Si). Optical characterization was performed using a laser at 659 nm and opportunely chosen filters to vary the optical power. A strong difference in the radiation damage effect is observed for the two different irradiation sources. Ion irradiation, or better implantation, produces a damage preferentially sitting in the active device region, hence even at the …