Energy resolution and non-proportionality of the light yield of pure CsI at liquid nitrogen temperatures

The energy resolution and non-proportionality of the light yield versus γ-ray energy of pure CsI scintillators directly coupled to Large Area Avalanche Photodiodes (LAAPDs) and cooled down to the liquid nitrogen temperatures have been studied. A very high light output above 1 00 000 ph/MeV was measured. One of the samples showed nearly proportional light yield response versus energy of γ-rays yielding energy resolution of 4.3±0.2% for 662 keV γ-rays from a 137Cs source. The intrinsic resolution of the crystals versus energy of γ-rays has been estimated by measurements of the number of primary electron-hole pairs generated in LAAPD by scintillation light. Inspection of the γ-ray-induced emission spectra of tested samples allows discussing different shapes of non-proportionality curves observed with various samples of CsI.