Development of high performance inorganic scintillator for gamma-ray spectroscopy

Abstract

To develop high performance inorganic scintillators for gamma-ray spectroscopy. In the first part of the experimental work, a dual zone vertical moving-temperature-gradient furnace was developed and applied to the Bridgman method. This technique helps to eliminate a driving mechanism leading to a reduction of vibrations which can adversely affect crystal growth quality. In the second part of the experimental work, charge preparation and equipment for growing process were developed. Crystal growth experiments of CsI:Tl, LaCl[subscript 3] :Ce and Ba[subscript 2] CsI[subscript 5] :Tl were performed. Tested results of the moving-temperature-gradient furnace illustrated that the growth zone exhibited a better thermal stability than the traditional Bridgman system. Only an error of less than 2% in the temperature gradient was found. The furnace was capable of growing simple CsI(Tl) crystal of is an empty set 22 × 22 mm size, starting from powder element of 99.9% purity, using 1 mm/hr growth rate with 25.5°C/cm temperature gradient and 2.5°C/hr temperature gradient drift rate. The analyzed crystal performance using the 662 keV energy of Cs-137 spectrum revealed the energy resolution of 7.53% and the intrinsic peak detection efficiency of 10.35% at 4.58:1 peak to Compton ratio. For LaCl [subscript 3] :Ce and Ba[subscript 2] CsI[subscript 5]:Tl grown crystals, the chemical activity of oxygen and moisture presented problem with charge preparation and affected crystal growth perfection, as grown crystals were foggy and cracked into small pieces. These experimental results were presented in this dissertation.