Scintillation characteristics of 90%Lu LGSO with different decay times

High lutetium content LGSO [Lu
_1.8
Gd
_0.2
SiO
₅
:Ce] with decay time constants in the range 30-45 ns were introduced by Hitachi Chemical Ltd. (Japan) around 2006. At first an experimental development, mass production has now been 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 the current production of 90%Lu LGSO with different decay times using avalanche photodiode (APD) readout. Samples from the most recent production of Fast (~30 ns), Standard (~40 ns) and Slow (~47 ns) 90%Lu LGSO (manufactured in 2013), extracted from top, middle and bottom positions into the ingots, have been studied. The decay time and central emission wavelength results demonstrate good agreement for samples of the same ingot, irrespective of the position where the sample was obtained. The photoelectron yields of the most recent Slow, Standard and Fast LGSO scintillators show good uniformity. Their average photoelectron yields are 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 average energy resolution of Slow is 10 ± 2% whereas Standard and Fast LGSO samples have identical energy resolution of 11 ± 3%. The light yield non-proportionality as a function of irradiation energy was investigated. At 60 keV, the departure from linearity is 16 ± 4% for Slow and Standard LGSO and 15 ± 1% for Fast LGSO.