Intrinsic energy resolution of pure NaI studied with large area avalanche photodiodes at liquid nitrogen temperatures

The energy resolution and non-proportionality of the light yield vs γ-ray energy of pure NaI scintillators directly coupled to Large Area Avalanche Photodiodes (LAAPDs) and cooled down to the liquid nitrogen temperatures have been studied. Large improvements of energy resolution and nearly proportional light yield response have been obtained at very long shaping time constants. Energy resolution of 3.8±0.1% for 662 keV γ-rays from a 137Cs source was recorded at 50 μs integration time. The intrinsic resolution of the crystal vs energy of γ-rays has been estimated by measurements of the number of primary electron–hole pairs generated in LAAPD by scintillation light.