The temperature dependence of gamma-ray responses of YAG:Ce ceramic scintillators

The temperature dependence (from -20 to +20 degrees C) of gamma-ray irradiated light outputs, energy resolutions, and decay time profiles of three YAG:Ce poly-ceramic scintillators are studied. The Ce concentrations are 0.5, 0.05, and 0.005 mol%. The relative light yield of the YAG:Ce with 0.5 mol% with a 2 mu s shaping time was measured as 1:1.08:1.14 at +20, 0, and -20 degrees C, respectively, including the temperature dependence of the phototube (-0.2%/degree). The energy resolution stays almost constant at 7.2%, for 662 keV gamma-rays. The ceramic with 0.05 mol% shows the almost same properties, while the light yield of that with 0.005 mol% is 2-4 times lower (hence the energy resolution becomes 14-19%). All the scintillators exhibit good linearities within similar to 1% between the light output and the irradiated gamma-ray energy from 59.5 keV to 662 keV. The decay time constants of the dominant decay components are about 80 ns and 300 ns at +20 degrees C. As the temperature increases from -20 to +20 degrees C, the effective decay of all the ceramics becomes faster, because the decay time constants and fractions of the slower components shorten and decrease, respectively. This result suggests that carriers which are captured in shallow traps before transferring excitation to Ce ions can escape the traps more easily at higher temperatures. Considering the decrease of the total light yield toward higher temperatures, it is thought that thermal quenching starts to dominate the temperature dependence of the ceramic YAG:Ce around the room temperature. The 0.5 mol% scintillator shows a lower quenching energy than the 0.05 mol% one. This can be explained in terms of self absorption of Ce emission.