Applied Moving-Temperature-Gradient Technique for CsI(Tl) Crystal Growth

Abstract

A simple high-temperature furnace with two independent heating zones was developed based on the moving-temperature-gradient concept with an operating range of 400 to 1,200 C. Programmable temperature reduction rates of the two heating zones are independently controlled in a closed chamber for better thermal stability throughout the growth zone. In order to eliminate the driving mechanism and reduce subtle vibration, which could adversely affect crystal quality, the charge crucible and furnace are made stationary during the growth process. Measurement results of temperature distributions of gradient drifting rates at various positions along the growth zone are presented. The growth of CsI(Tl) scintillation crystals prepared from a mixture of 99.9% pure CsI powder and Tl powder, using the growth rate of 1 mm/h, temperature gradient of 25.5 C/cm, and temperature gradient drift rate of 2.5 C/h, was achieved with crystal sizes of 10 and 22 mm diameter, both 70 mm in length. Test results of gamma energy resolution at 662 keV of Cs-137 spectrum measurement revealed a resolution of 7-9%.