Scintillator geometry and surface treatment for readout by a small area silicon photomultiplier

New solid state photomultipliers (SSPM) allow small radiation detectors to be more easily realized. Their compact, rugged, and simple operation are inherent advantages over the traditional photomultiplier tube. Because the cost and dark counts of SSPMs scale with area, we are investigating scintillation light read out from a fraction of one face of a scintillating crystal. The Monte Carlo optical transport code DETECT2000 [1,2] was used to track optical photons within the scintillator volume. A MATLAB interface was developed for DETECT2000 to facilitate parametric simulations of complex geometries. We examined the reflectivity of a 3 M mirror film and found it to be comparable to Teflon tape for certain wavelengths. Large crystals can be read out by small photodetectors with some degradation in the light collected. For small changes in size, light is lost approximately in proportion to the crystal-to-SSPM length ratio. For dosimetry applications, an effective brightness parameter was proposed which integrates the collected light yield for a uniform distribution of incident energies. A crystal twice the length of a 3 times 3 mm² SSPM was determined to be optimal for a 50 to 1500 keV radiation field normally incident on a Teflon-wrapped cubic LYSO crystal. By maximizing the photofraction and minimizing the photostatistical energy resolution, the optimal crystal-to- SSPM ratio was determined to vary with the energy of interest for spectroscopic applications.