Temperature dependence of CSl(TI) gamma-ray excited scintillation characteristics

The gamma-ray excited, temperature dependent scintillation characteristics of CsI(Tl) are reported over the temperature range of -100 to +50°C. The modified Bollinger-Thomas and shaped square wave methods were used to measure the rise and decay times . Emission spectra were measured using a monochromator and corrected for monochromator and photocathode spectral efficiencies . The shaped square wave method was also used to determine the scintillation yield as was a current mode method . The thermoluminescence emissions of CsI(TI) were measured using the same current mode method . At room temperature, CsI(T1) was found to have two primary decay components with decay time constants of T1=679±10 ns (63.7%) and T z = 3.34±0.14 Ws (36.1%), and to have emission bands at about 400 and 560 rim . The T1 luminescent state was observed to be populated by an exponential process with a resulting rise time constant of 19.6±1 .9 ns at room temperature. An ultra-fast decay component with a < 0.5 ns decay time was found to emit about 0.2% (about 100 photons/MeV) of the total scintillation light . Except for the ultra-fast decay time, the rise and decay time constants were observed to increase exponentially with inverse temperature . At -80°C T1 and TZ were determined to be 2.22±0.33 ws and 18.0±2.59 ws, respectively, while the 400 rim emission band was not observed below -50°C. At +50°C the decay constants were found to be 628 ns (70.5%) and 2.63 ws (29.3%) and both emission bands were present . The scintillation yield of CsI(TI) was observed to be only slightly temperature dependent between -30 and +50°C, peaking at about -30°C (about 6% above the room temperature yield) and monotonically decreasing above and below this temperature . Four different commercially available CsI(TI) crystals were used . Minimal variations in the measured scintillation characteristics were observed among these four crystals . Thermoluminescence emissions were observed to have peak yields at -90, -65, -40, +20, and possibly -55°C. The relative magnitudes and number of thermolummescence peaks were found to vary from crystal to crystal .