Energy Resolution and Non-proportionality of Scintillation Detectors
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1038-O07-02
Energy Resolution and Non-proportionality of Scintillation Detectors Marek Moszyñski Department of Detectors and Nuclear Electronics, Soltan Institute for Nuclear Studies, Swierk, Otwock, PL 05-400, Poland ABSTRACT The limitation of energy resolution of scintillation detectors are discussed with a special emphasis on non-proportionality response of scintillators to gamma rays and electrons, which is of crucial importance to an intrinsic energy resolution of the crystals. Examples of the study carried out with different crystals and particularly those of tests of undoped NaI and CsI at liquid nitrogen temperature with the light readout by avalanche photodiodes are presented suggesting strongly that the non-proportionality of the halide crystals are not their intrinsic property. Moreover, the influence of slow components of the light pulses on energy resolution and nonproportionality are discussed. INTRODUCTION A γ-ray spectrometry with scintillation detectors belongs to the most important methods in the research and different applications of nuclear science. It covers, for example, a basic study of nuclear physics, environmental study, nuclear medicine and recently homeland security equipment. A great importance of scintillation detectors is associated with their high detection efficiency for nuclear radiation, capability to measure energy spectra, the possibility to work with a very high counting rate up to 107 counts/s and achievable best time resolution in coincidence or time-of-flight experiments. Capability to detect a wide assortment of radiations including γ and X-rays, charged particles and neutrons, the great variety in size and constitution of scintillators make them as the best choice in different applications [1]. For the γ-ray spectrometry the following properties of scintillation materials are essential [2]: • A high density of the material and a high atomic number of the major element assuring high detection efficiency of γ-rays and a high photofraction, • A high light output responsible for the high statistical accuracy of delivered signal, • A fast decay time of the light pulse reflecting decay time of fluorescence components of the crystal, and allowing for a high counting rate measurements, • A low contribution of the scintillator to the measured energy resolution associated mainly with its non-proportionality characteristics. Three first properties are straightforward, as they are described by the basic properties of a scintillator. Energy resolution achievable with different crystals is the most mysterious. It is a function of the light output but it is also affected by internal properties of scintillator. A good energy resolution is of the great importance for most of applications of scintillation detectors. Thus, its limitations are discussed below with a special emphasis on non-proportional response of scintillators to gamma rays and electrons, as it is of crucial importance to an intrinsic energy resolution of the crystals. An important influence of the scattering of secondary el
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