Performance of CsI(Na) scintillators in γ-Ray spectrometry

An optimization of the performance of CsI(Na) scintillators coupled to a photomultiplier and irradiated by γ rays is presented. Earlier studies showed that scintillators exhibiting two or more light pulse components in the deexcitation process (e.g. CsI(Tl), Nal(Tl) in reduced temperatures) perform better when longer integration time is set in the amplifier. Such properties like energy resolution and non-proportional response improve while lengthening shaping time in the amplifier. At 12 μs shaping time constant the measured energy resolution for a special grade ?1"? 1" CsI(Na) sample was as good as 5.8±0.1%. Light pulse shape measurements showed that CsI(Na) scintillators irradiated by spl gamma/ rays deexcite mostly in the microsecond range and the light pulse consists of three components: ˜470 ns (fast), ˜1.8 μs (slow) and ˜8 μs (tail) with the relative intensities about 41%, 28% and 31%, respectively. From the point of view of a potential use of CsI(Na) in homeland security applications the crystal was compared to commonly used Nal(Tl) with taking into account such parameters as: energy resolution, non-proportionality, photopeak efficiency and others.