Scintillation and Spectroscopic Characteristics of 90%Lu LGSO With Variable Decay Times

High lutetium content LGSO [Lu
_1.8
Gd
_0.2
SiO
₅
:Ce] scintillators with decay time constants in the range 30-45 ns were introduced some ten years ago. At first an experimental development, mass production was gradually established and mature 90%Lu LGSO scintillators with stable characteristics have become available. The aim of this work was to assess the scintillation characteristics of recent 90%Lu LGSO production with different decay times using avalanche photodiode (APD) readout. Samples of Fast (~30 ns), Standard (~40 ns) and Slow (~47 ns) 90%Lu LGSO, extracted from top, middle and bottom positions into ingots, have been investigated. The decay time and central emission wavelength were found to be stable for samples from the same ingot, irrespective of the position where the sample was obtained. The photoelectron yields of Slow, Standard and Fast LGSO scintillators generally showed good uniformity. Their average photoelectron yields at 511 keV were respectively 34 000 ± 1 000 phe/MeV, 31 200 ± 500 phe/MeV and 28 000 ± 2 000 phe/MeV without any definite trend or bias with respect to position in ingots. The combination of photon yield and decay time results in high initial emission rate and a subnanosecond time resolution performance of 914 ± 18 ps for the three categories of decay times. The average energy resolution at 511 keV of Slow LGSO was 10 ± 2% whereas Standard and Fast LGSO samples had identical energy resolution of 11 ± 3%. The light yield non-proportionality as a function of irradiation energy was also investigated. At 60 keV, the departure from linearity reached 19 ± 2%.