Citation:
W. Schmidt, “Testing the Benefits of Using Silicon Photomultipliers on Organic Scintillator Portal Monitors”, M.S. Thesis, Nuclear Engineering, Texas A&M University, College Station, TX (2024).
Abstract:
Rapid and accurate detection of radiation at checkpoints is of vital importance to national security. One proposed method for improving radiation detection capabilities is using Silicon Photomultipliers (SiPMs) on the organic scintillation panels used at checkpoints to detect radiation. Research on SiPMs has been relegated to small detectors with volumes in the cubic millimeter range, but large portal monitors are often used at ports of entry and traffic control points to monitor radiation. This research examined the efficacy of SiPMs placed on larger plastic scintillators with volumes orders of magnitude larger than previous tests have analyzed. For this research two arrays of SiPMs were determined to be the most advantageous due to superior intrinsic efficiency and were tested on plastic scintillators using three different gamma emitting isotopes. Experiments testing a single SiPM to a PMT when placed in geometrically similar configurations gave an average SiPM to PMT total count ratio of 0.0963 ± 0.0006 for the highest-energy gammas, which was within 5% of the expected value based on the ratio of the active areas of the single SiPM and PMT. However, when two arrays of SiPMs were selected based on numerical simulations and tested, the best ratio of SiPM to PMT total count ratio for a single array observing a source was 0.394 ± 0.001, which was within 5% of the active area ratio. SiPM arrays and PMTs were also compared by the ratio of source counts to background counts observed for each isotope, with the best SiPM array observing a ratio of 1.391 ± 0.003 while the PMT’s ratio was 1.584 ± 0.003 for the same isotope. Ultimately, the results of the study do not suggest that SiPMs are an optimal substitute for PMTs on large-volume plastic scintillators, but this result is not concluded decisively by the experiment’s results.