Suren Kandasamy Dissertation.pdf - University of Surrey

M.Sc DissertationGas-filled Detectors are based on sensing the direct ionization created by thepassage of the radiation. These detectors can divide into three groups such as,Ionization chambers, proportional counters, and Geiger-Muller counters. TheIonization chambers are used to measure exposure to X-rays and gamma-rays. Oneimportant application of proportional counters has therefore been in the detection andspectroscopy of low-energy X-radiation. Proportional counters are also widely appliedin the detection of neutrons. Since helium-3 and boron have very high detectionefficiency for thermal neutrons, 3 He, BF 3 tubes are used as gas-filled detectors.2.2 ScintillatorsSome materials have the ability to release visible or UV light when de-excitedafter an excitation caused by a photon or charged particle. The emission of photons bythe atom of the materials is only a portion of the total energy deposited in the absorber.The rest of the energy is stored as thermal energy in the absorber. This type of materialsis called a scintillator and is widely used in nuclear medicine.The most widely applied scintillators include the inorganic alkali halide crystal.The inorganics tend to have the best light output and linearity, but with severalexceptions are relatively slow in their response time. Organic scintillators are generallyfaster but yield less light. The high Z-value of the constituents and high density ofinorganic crystal favour their choice of gamma-ray spectroscopy, whereas organics areoften preferred for beta spectroscopy and fast neutron detection [1]. The light yield(light output) of the scintillator is expressed as photons per MeV of absorbed gammarayenergy. The light output is the most important, as it affects both the efficiency andresolution of the detector. Main problems in creating effective scintillator gamma-raydetectors are the need for high energy resolution in order to make precise identificationof any source, and high efficiency in order to minimise the acquiring time needed forthe necessary resolution. This can be achieve with high light output scintillators, such asnew cerium doped lanthanum halide scintillators.K. Suren 4