Study of NaI(Tl) scintillator cooled down to liquid nitrogen temperature

Since early 50's NaI(Tl) scintillators have been commonly used in many branches of physics and industry due to their relatively low price, high light output and fair energy resolution. Through this period of time, both spectroscopic and luminescence properties of NaI( Tl) were measured at room temperature. In this work, the gamma spectrometry and the luminescence properties of the NaI(Tl) at LN2 temperature were studied. The gamma spectrometry was carried out with the light readout by avalanche photodiodes cooled down together with the crystal in the cryostat. It was observed that non-proportionality measured at LN2 temperature is significantly better than that at room temperature. The energy resolution of the NaI( Tl) at 662 keV measured at LN2 temperature was estimated to be 6.57%, comparable to that measured commonly at RT with photomultipliers. A decay time measurement of the NaI( Tl) at LN2 showed a slower decay of 736 +/- 10 ns.