A light detector working as photon counter.
The knowledge of the diffuse Night Sky Background light (NSB) level in the UltraViolet energy region is a necessary step in the analysis of cosmic rays detected by fluorescence experiments as well as in the case of Cherenkov telescopes. The NSB light depends on the geographic and atmosphere conditions, including humidity, pressure, dusts, airglow, moonlight, stars and planets, and so on. In particular, the environmental conditions influence the atmosphere composition and therefore can induce significant variations in the fluorescence yield, arising in uncertainty in the cosmic ray energy reconstruction.
The measurement of the diffuse NSB in the UV energy region (300-400 nm, roughly) is therefore a complementary and integrating part of the activities of the “cosmic rays and TeV gamma-ray astronomy” group of IASF-Palermo. This activity, started in 1998 with the balloon-born experiment BaBy (Background Bypass), was subsequently performed through ground-based observations, firstly with the so-called “Baby on-ground,” and, since 2003, with the UVscope instrument.
The UVscope instrument is essentially a light detector working as photon counter. Its sensitive unit is a high speed response photomultiplier with efficiency extended to the UV band. A UVscope unit is currently active in the framework of the ASTRI program to monitor the NSB diffuse light of the Serra La Nave site where the ASTRI telescope prototype is installed.