GAMMA-RAY SPECTROSCOPY AND TIMING USING LSO AND PIN PHOTODIODES

The high density, highlight output, and short decay time of LSO (lutet ium orthosilicate, Lu2SiO5:Ce) make it an attractive scintillator for gamma ray spectroscopy. The low cost, small size, high quantum efficie ncy, and ruggedness of silicon photodiodes make them attractive photod etectors for this same application, although their high noise (compare d to a photomultiplier tube) reduces their appeal. In this work we mea sure the gamma ray energy resolution, timing accuracy, and conversion factor from gamma energy to number of electron-hole pairs produced wit h a 3x3x22 mm(3) LSO scintillator crystal read out with a 3x3 mm(2) si licon PIN photodiode. When the detector is excited with 511 keV photon s, a photopeak centered at 1940 e(-) with 149 keV fwhm is observed and a timing signal with 35 ns fwhm jitter is produced. When the detector is excited with 1275 keV photons, a photopeak centered at 4910 e(-) w ith 149 keV fwhm I is observed acid a timing signal with 25 ns fwhm ji tter is produced. While these performance measures are inferior to tho se obtained with photomultiplier tubes, they are acceptable for some a pplications.