Silicon photomultipliers in radiation sensing applications

Abstract

The Silicon Photomultiplier (SIPM) is a novel photon sensing device, with potential applications in particle physics, astronomy and general gamma-ray spectroscopy.
Various SiPM designs were evaluated for these roles by coupling them to a range of scintillators, including LSO, NaI(Tl) and CsI(Tl). It was found that a LSO-SiPM gamma-ray detector provide sufficiently good energy resolution (11% at 511keV) in a very compact package to be of interest in PET imaging. SiPMs awere also found to provide competitive spectra to PIN diodes of comparable area (1cm2) when coupled to CsI(Tl), raising interest in gamma-ray astronomy where a CsI(Tl)-SiPM detector could be used as an imaging element.

Good performance with CsI(Tl) encouraged investigation of SiPMs in the gamma-ray spectroscopy role, specifically radioisotope identification with portable instruments. The ScintiSphere concept was exploited to allow a larger, more sensitive detector to be built using SiPMs without sacrificing spectral quality. An 8cc sphere of CsI(Tl) coupled to a 1cm2 SiPM array was found to give a noise floor of 35keV and a resolution of 9% at 662keV, closely comparable to a 0.8cc square crystal, despite the factor of 10 improvement in sensitive volume. Neutron detection with a SiPM array is achieved using LiI(Eu), which was found to resolve thermal neutron captures to 12% FWHM and achieve excellent gamma-ray rejection. In this application, SiPMs are preferable to PIN diodes as they are immune to direct gamma-ray interactions which could degrade gamma-ray rejection. When packaged in a compact moderator of 15mm depth and volume 58cc of HDPE, a compact neutron counter was built and found to be slightly more efficient than a 3” He3 tube packaged in 16mm of HDPE.

Finally, an instrument is proposed that exploits the intrinsic advantages of SiPMs. The use of SiPMs with LaBr(Ce) is explored and simulations are carried out of a directional spectrometer, predicted to locate a Cs137 source of 1mC at 2m to within 15° in 15 seconds. In conclusion, it is found that SiPMs should be of great interest in these fields due to providing comparable performance to existing systems whilst providing additional benefits such as low power electronics, high gain and immunity to direct X-ray interactions.

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Identifiers

ORCID for Anthony J. Bird: orcid.org/0000-0002-6888-8937

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