Compact inexpensive gamma spectrometer based on silicon photomultipliers

The aim of this study is to develop and test a prototype miniature gamma spectrometer based on silicon photomultipliers (SiPMs). Such a device could potentially be made small and inexpensive enough to be essentially disposable, allowing the deployment of thousands of radiation detection units in remote areas where manned surveillance is unfeasible. In this work we investigate only the spectroscopy performance of silicon photomultipliers at room temperature, and do not consider issues of data transmission, protection from the elements, etc. Two such devices have been built and tested. The first consists of two 2 × 2 arrays of 3 mm × 3 mm SiPMs from Photonique, mounted on opposite faces of a 1 cm × 1 cm × 1 cm CsI(Tl) crystal. Using 8 SiPMs is intended to improve light collection from the scintillator as well as to expand the dynamic range by increasing the number of microcells. The four signals from each side are summed and acquired in coincidence mode - while multiplying the number of SiPMs increases the total electronic noise, we investigate whether using coincidence gating could ultimately reduce noise and allow detection of low energy photons. The second spectrometer consists of two 3 mm × 3 mm SiPMs from Hamamatsu coupled to opposite faces of a 4 mm × 4 mm × 10 mm LYSO crystal. The two signals are also acquired in coincidence. The gated spectra are compared to non-gated, background-subtracted summed spectra to evaluate the usefulness of coincidence for noise reduction. For both setups, we obtain gamma spectra for five different isotopes (Na-22, Cs-137, U-238 (as depleted uranium, or DU), Co-57, Ba-133, and also F-18 and Tc-99m for the Hamamatsu devices). For comparison, spectra for these sources are also acquired using the same scintillators on a PMT. Again, all spectra are acquired at room temperature.