Study of pure NaI at room and liquid nitrogen temperatures

• Three pure NaI crystals grown in different batches by Scionix (The Netherlands) 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 poises 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 nonproportionality of the light yield. The fast light pulse had the main decay time components of 1 and 5 ns. The high initial photon intensity of the tested NaI crystals revealed a good timing. resolution of about 140 ps obtained for Co-60 gamma-rays. At. liquid nitrogen temperatures the measurements of light yield and energy resolution were performed using An Advanced Photonix, Inc. avalanche photodiode readout A high light output above 80 000 ph/MeV was measured for the best of the tested crystals. The energy resolutions of the 662 kAV photopeak of the three crystals differ a lot, varying from an excellent value of 3.8% to 6.2%. This suggests that the measured, pies energy resolutions depend on the purity of the scintillator samples reflected in the emission spectral The studies that were performed demonstrate the attractive properties of pure NaI at both room and LN2 temperature.

Nyckelord

avalanche photodiodes (APDs)

energy resolution

nonproportionality of light yield

pure NaI scintillators

area avalanche photodiodes

intrinsic energy resolution

scintillation response

non-proportionality

sodium-iodide

decay time

csi

photomultipliers

crystals

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