Gamma ray spectroscopy and timing using LSO and PIN photodiodes

The high density, high light output, and short decay time of LSO (lutetium orthosilicate, Lu₂SiO₅:Ce) make it an attractive scintillator for gamma ray spectroscopy. The low cost, small size, high quantum efficiency, and ruggedness of silicon photodiodes make them attractive photodetectors for this same application, although their high noise (compared to a photomultiplier tube) reduces their appeal. In this work we measure the gamma ray energy resolution, timing accuracy, and conversion factor from gamma energy to number of electron-hole pairs produced with a 3×3×22 mm³ LSO scintillator crystal read out with a 3×3 mm² silicon PIN photodiode. When the detector is excited with 511 keV photons, 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^- with 149 keV FWHM is observed and a timing signal with 25 ns FWHM jitter is produced. While these performance measures are inferior to those obtained with photomultiplier tubes, they are acceptable for some applications