Application of Silicon Photomultipliers in Neutron Detectors

Advancement in the development of semiconductor photodetectors have led to substitution of Photomultiplier Tube (PMT) technology by solid state devices in many applications. Silicon Photomultipliers (SiPM) are solid-state photodetectors with a gain similar to PMT and that have several advantages over the PMTs like low operating voltages and insensitivity to magnetic fields. However, concerns of radiation damage induced in Silicon due to neutron radiation required a deeper understanding in order the SiPMs to become a suitable technology for neutron detector systems. This work provides an insight into effects of cold neutron irradiation on the important macroscopic characteristics (dark count rate (DCR), photon detection efficiency (PDE) and timing resolution (TR)) of SiPMs and its quantification for two analog samples manufactured respectively by SensL - ON Semiconductor and Hamamatsu Photonics, and one digital SiPM (Philips Digital Photon Counting, PDPC) from Koninklijke Philips N.V. Further, it describes the development of a large cold/thermal neutron scintillation detector prototype, with an active area of 13.6 cm × 13.6 cm, utilizing the digital SiPM (PDPC) modules and a 6Li glass scintillator. The goal of the development is to have a neutron (5 A ˚ ) detection efficiency of > 75 %, a possible count rate of > 2 kcps/cm2, and a spatial resolution of minimum 1 mm × 1 mm. In order to achieve the targeted spatial resolution a light guide was introduced between the SiPM array and the scintillator glass. Geant4 simulations were performed in advance for optimization of the setup. The simulation results were verified by comparing simulation data with measurement results obtained at the research reactor BER-II of HZB Berlin and FRM-II of TU Munich in Garching. Additionally, the overall performance of the detector prototype is evaluated, which finds the prototype to exceed (neutron detection efficiency > 95 %, 100 kcps/cm2 count rate and 1 mm × 1 mm spatial resolution) the specified goals. Furthermore, customized position reconstruction algorithms were developed, based on comparison of simulation and measurement data, and implemented for the targeted neutron detection resolution with a precision of 1 mm. Subsequently, the efficacy of the algorithms were compared for the given detector prototype.