Applications of Silicon Photomultipliers in Personal Radiation Detection and Nuclear Imaging

Sanchez-Fortun Stoker, Jamie
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Faculty of Graduate Studies and Research, University of Regina

Originally developed as the readout for calorimeters in high-energy physics experiments, the silicon photomultiplier (SiPM) has found use in a wide range of fields requiring the detection of low-intensity light. This thesis discusses work on two such applications: in the development of a prototype personal radiation detector (PRD), and in the imaging of a radioactive source. The ability to detect above-background levels of radiation has received increased attention in recent years, not least from the perspective of national security agencies in, for example, tracking the movement of illicit radioactive materials, or in dealing with potential fall-out from nuclear accidents. In such potentially hazardous environments, there has been an increased demand for improved PRDs for use by emergency workers and first-responders. Motivated by an NSERC-funded partnership with Environmental Instruments Canada Inc. (EIC), the first part of this thesis focuses on a project to develop a small, low-cost, easy-to-use prototype gross-counting gamma-radiation detector based upon SiPM technology. Limited by size and cost requirements, measurements suggested the Hamamatsu S12572-050C model (3 3 mm2) as the preferred choice of SiPM, and subsequent work tested several SiPM/lightproducing medium combinations. A PTFE (teflon)-wrapped common plastic scintillator (BC-416), coupled to the SiPM, was identified as the medium providing the most significant sensitivity enhancement with respect to EIC’s existing detection device (incorporating a Geiger-Müller tube as its photosensor), while minimising cost and maintaining the overall physical size of EIC’s detector. An additional project positively assessed the suitability of SiPMs for thermal neutron detection using scintillating fibres coated in successive layers of zinc sulphide and boron carbide. The second part of this thesis (funded through the Sylvia Fedoruk Centre for Nuclear Innovation) presents a preliminary characterisation of two SensL MatrixSM-9 SiPM array modules, in preparation for their use in a “PhytoPET” plant-imaging system to be built at the University of Regina. Such arrays of SiPMs are now available commercially as part of modular, turnkey readout systems designed specifically for use in high-resolution, state-of-the-art medical-imaging applications. However, PET systems designed to image plants – such as the (operational) PhytoPET system based at Duke University – typically utilise multi-anode photomultiplier tubes. Singles measurements are reported for each SiPM array, coupled in turn to a PTFE-wrapped BC-416 plastic scintillator in several configurations. Pixelated images of noise and various laboratory sources are reconstructed from output data files using dedicated codes, and the array-trigger error of each module is mapped over a wide-range of adjustable array and pixel thresholds.

A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Physics, University of Regina. xi, 139p.