Study of pure NaI at room and liquid nitrogen temperatures

Abstract

Three pure NaI crystals grown in different batches by Scionix (Holland) were studied at room and liquid nitrogen temperatures. The room temperature studies performed with photomultiplier readout covered measurements of emission spectra, photoelectrons yield and energy resolution. Moreover, the scintillation light pulses were measured by single photon method. Two crystals showed the photoelectron yield of about 1000 phe/MeV measured at room temperature with an XP2020Q photomultiplier. The energy resolution of the 662 keV photopeak was measured to be about 16% and was limited mainly by a low number of photoelectrons and a large non-proportionality of the light yield. The fast light pulse had the main decay time components of 1 ns and 5 ns. The high initial photon intensity of the tested NaI crystals revealed in the good timing resolution of about 140 ps obtained for 60 Co γ γ γ γ-rays. At liquid nitrogen temperatures the measurements of light yield and energy resolution were performed using Advanced Photonix, Inc. avalanche photodiode readout. A high light output above 80000 ph/MeV was measured for the best of the tested crystals. The energy resolutions of the 662 keV photopeak of the three crystals differ a lot, varying from an excellent value of 3.8 % to 6.2 %. This suggests that the measured energy resolutions depend on the purity of the scintillator samples reflected in the emission spectra. The studies that were performed demonstrate the attractive properties of pure NaI at both room and LN 2 temperature.

Measurements of NaI(Tl) Electron Response: Comparison of Different Samples

“…Fig. 4 also shows the undoped NaI emission spectrum measured by Moszynski et al [18], showing a pure exciton band; The comparison with this spectrum clearly indicates that the satellite peaks observed in the spectra acquired in this work are not due to the exciton band typical of undoped NaI that appears at 310 nm. Fig.…”

“…The emission spectrum for pure NaI as measured by Moszynski et al (ref. [18]) is reported for comparison. In the insert the Gaussian fit for the Saint-Gobain crystal #568 is presented, as an example.…”

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

“…This allowed use of the 5.9 keV X-ray peak from a 55 Fe source as the reference to measure a number of e-h pairs produced by scintillation light [1]. It is worth to stress a very good energy resolution of 4.370.1%, however, somewhat poorer than that observed with the best pure NaI [2,3].…”

“…In the previous papers we have shown excellent properties of pure NaI scintillator at liquid nitrogen (LN 2 ) temperature [1][2][3]. A high light output above 80 000 ph/MeV and the energy resolution for the 662 keV photopeak of 3.8% were measured for the best crystals.…”

“…The problem was solved by the application of Large Area Avalanche Photodiodes (LAAPD) operating at LN 2 temperatures [7,8] showing excellent properties, particularly in the study of scintillators at LN 2 temperatures [1][2][3]7,8].…”