Compton suppression system with asymmetric NaI/BGO guard detectors
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The IAEA introduces safeguards to prevent the diversion of nuclear materials and related facilities, ensuring their peaceful use. Nuclear material control and accountability (NMCA) quantifies nuclear materials and monitors their inventories. Gamma-ray spectroscopy is a widely used non-destructive assay (NDA) technique for NMCA, capable of identifying isotopic compositions and relative intensities. However, measured spectra are often distorted when significant peaks are buried within the Compton continuum. To address this issue, a Compton suppression system (CSS) based on anti-coincidence counting is employed. In this study, low-energy peaks (90–130 keV) from characteristic X-rays of U and Pu, significantly affected by the Compton continuum from Cs- 137 (662 keV gamma-ray emitter), were defined as the region of interest (ROI) for spent nuclear fuel (SNF) assessment. A novel CSS design was developed by integrating NaI and BGO detectors around an HPGe detector. Experimental results and MCNP simulations showed that the asymmetric NaI/BGO CSS achieved a higher Compton suppression factor in low-energy regions compared to conventional BGO detector-only CSS. The results highlight the effectiveness of this design in suppressing the Compton continuum and reveal additional peaks that were previously obscured.
Abstract
The IAEA introduces safeguards to prevent the diversion of nuclear materials and related facilities, ensuring their peaceful use. Nuclear material control and accountability (NMCA) quantifies nuclear materials and monitors their inventories. Gamma-ray spectroscopy is a widely used non-destructive assay (NDA) technique for NMCA, capable of identifying isotopic compositions and relative intensities. However, measured spectra are often distorted when significant peaks are buried within the Compton continuum. To address this issue, a Compton suppression system (CSS) based on anti-coincidence counting is employed. In this study, low-energy peaks (90–130 keV) from characteristic X-rays of U and Pu, significantly affected by the Compton continuum from Cs- 137 (662 keV gamma-ray emitter), were defined as the region of interest (ROI) for spent nuclear fuel (SNF) assessment. A novel CSS design was developed by integrating NaI and BGO detectors around an HPGe detector. Experimental results and MCNP simulations showed that the asymmetric NaI/BGO CSS achieved a higher Compton suppression factor in low-energy regions compared to conventional BGO detector-only CSS. The results highlight the effectiveness of this design in suppressing the Compton continuum and reveal additional peaks that were previously obscured.