Abstract
The helium-3 world crisis requires a development of new methods of neutron detection to replace commonly used 3He proportional counters. In the past decades, great effort was made to developed efficient and fast scintillators to detect radiation. The inorganic scintillator may be an alternative. Inorganic scintillators with much higher density should be selected for optimal neutron detection efficiency taking into consideration the relevant reactions leading to light emission. These detectors should, then, be carefully characterized both experimentally and by means of advanced simulation code. Ideally, the detector should have the capability to separate neutron and gamma induced events either by amplitude or through pulse shape differences. As neutron sources also generate gamma radiation, which can interfere with the measurement, it is necessary that the detector be able to discriminate the presence of such radiation. Considerable progress has been achieved to develop new inorganic scintillators, in particular increasing the light output and decreasing the decay time by optimized doping. Crystals may be found to suit neutron detection. In this report, we will present the results of the study of lead doped cesium iodide crystals (CsI:Pb) grown in our laboratory, using the vertical Bridgman technique. The concentration of the lead doping element (Pb) was studied in the range 5х10-4 M to 10-2 M . The crystals grown were subjected to annealing (heat treatment). In this procedure, vacuum of 10-6 mbar and continuous temperature of 350°C, for 24 hours, were employed. In response to neutron radiation, an AmBe source with energy range of 1 MeV to 12 MeV was used. The activity of the AmBe source was 1Ci Am. The fluency was 2.6 х 106 neutrons/second. The operating voltage of the photomultiplier tube was 1700 V; the accumulation time in the counting process was 600 s and 1800 s. The scintillator crystals used were cut with dimensions of 20 mm diameter and 10 mm height.
Highlights
The disappearing inventory and minute natural abundance of 3He gas necessitate the adoption of new technologies for the detection of neutrons
In the role of an activator, the dopant ion may be the luminescence species or may promote luminescence as in the case of defect bound exciton emission. [3,2] Scintillators based on cesium iodide are the leading, among materials available for solid-state detectors
Cesium iodide based scintillators have high luminescence yield accompanied by high energy resolution and radiation stability
Summary
The disappearing inventory and minute natural abundance of 3He gas necessitate the adoption of new technologies for the detection of neutrons. The luminescence may be intrinsic to material and involve electron-hole recombination; free, self trapped, and defecttrapped exciton luminescence; constituent transition group per post transition group ion fluorescence; core-valence band transitions; or charge transfer transitions within a molecular complex. It may be extrinsic, such as luminescence associated with impurities or defects and additive dopant íons. Various impurities have benn incorporated into alkali halides and their effects on optical properties and radiation detection have been investigated Ions such as Tl+, Br-, Li+, Pb2+ has been the theme of pursuit in our laboratory, in the last years. A systematic investigation has been carried out in Pb2+ doped cesium iodide crystal to neutron response and the results are discussed in this article
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