Online program Overview Session: NSS-18

Abstract

Advancements in Silicon Photomultiplier (SiPM) performance in recent years have demonstrated success across a broad range of fields, including particle and nuclear physics, Positron Emission Tomography, Light Detection and Ranging technology, Fusion diagnostics, among others. This work develops a time-of-flight (ToF)–based neutron spectrometer using SiPMs coupled to plastic scintillators as a plasma fusion diagnostic tool. A Deuterium-fueled plasma fusion emits 2.45MeV neutrons with an energy spectrum broadened by ion kinematics. The achievable neutron energy resolution of the spectrometer is correlated to the relative uncertainty on the inferred plasma ion temperature, a critical parameter for evaluating plasma performance and viability of the fusion approach. The target relative uncertainty on temperature is below 20%, therefore constraining the neutron interaction time and position resolution within the spectrometer. A two-layer (L1–L2) detector array is in development at TRIUMF. The detector coupled with fast data acquisition is expected to successfully detect neutrons at GHz rate. Timing-Position resolution of the chosen scintillators (Eljen L1: EJ232Q 0.5% Benzophenone doped; L2: EJ230) paired with Broadcom series AFBR-S4N SiPMs is presented as proof of concept in the neutron energy range of interest. A 511keV-gamma source is used to characterize the timing and position response of a single scintillator–SiPM assembly, incorporating the light yield differences between gamma and neutron interactions accounted for via Birks' law. Techniques and results demonstrating time resolution ranging 60 to 120ps with energy in Layer 1 and preliminary work on Layer 2 will be presented.

Abstract

X-ray dark-field (DF) imaging enables detection of low-Z scattering materials such as powdered explosives and narcotics, which are indistinguishable in conventional absorption imaging, making it a transformative technology for security screening. However, industrial baggage scanners face an inherent trade-off: high-throughput operation requires large-pixel detectors to capture sufficient photon flux at 160 kV operating voltages, but this causes severe Moiré fringe blurring that fundamentally limits DF sensitivity. In our previous work, we developed a 160 kV dark-field baggage scanner prototype, but found that the 2.7 mm × 3.0 mm large-pixel detectors we used only achieved a fringe visibility of ~7.3% under practical operating conditions, severely limiting DF sensitivity. To address this bottleneck, this study quantitatively investigates pixel size-induced visibility degradation through physics-informed simulations and experimental validation on a benchtop grating interferometry platform. Results confirm the visibility decay trend predicted by the sinc model, and show that a 0.5 mm small-pixel detector achieves ~30% improvement in DF sensitivity for high-energy X-ray dark-field baggage scanners. This work provides critical quantitative guidance for optimizing these systems to improve hazardous material detection.

Abstract

Nuclear material safeguards demand portable, isotope specific verification methods capable of operating across diverse deployment contexts. Neutron Resonance Transmission Analysis (NRTA) exploits isotope-specific resonances in neutron cross sections to provide definitive material identification, but portable implementations have been constrained to one-dimensional areal density measurements. Here we present a compact pixelated NRTA system that achieves three-dimensional isotopic imaging through a deuterium-tritium neutron generator, a multi-element GS20 $^6$Li scintillator array, and Algebraic Reconstruction Technique (ART) algorithms. Systematic benchmarking establishes operational limits: maximum target dimensions of 17.5 × 17.5 × 17.5 cm, stand-off distances up to 17.5 cm, spatial resolution of 2.5 cm, and complete three-dimensional reconstruction within four hours using eight measurement angles at 30 minutes per angle. Three-dimensional reconstruction of both homogeneous and non-homogeneous tungsten and silver targets is demonstrated experimentally. This system extends portable NRTA beyond one-dimensional assay, enabling field-deployable isotopic imaging previously available only at large centralized neutron facilities.

Abstract

Diffraction contrast tomography is used extensively on x-ray scattering instruments, however, its neutron counterpart has up till now been elusive, in part due to detector limitations. Scintillator-coupled Timepix detectors offer high spatial resolution, event-mode readout, and improved rate capability, making them attractive for neutron scattering and imaging applications. Here we evaluate a LumaCam detector equipped with a TPX3Cam and a ZnO:Zn:6LiF scintillator in a near-field diffraction setup. Scintillation light was focused in a lens onto a 25mm-diameter MCP-based image intensifier. Intensified light was refocused onto a 0.3mm-thick Si sensor with a thin window bonded to a Timepix3 ASIC. Hits were collected in and clusterie to increase position resolution beyond the native pixelation of the ASIC. The detector was placed 10 cm from the sample at 90 degrees to the beam and calibrated using a silicon powder sample. A refractory alloy sample with grains up to 1mm was measured over 180 degrees of rotation. Diffraction spots were assigned to reflections from several crystallographic orientations. By correlating angular separations and relative intensities, 75 grains were identified. Results demonstrate the feasibility of compact grain-resolved neutron diffraction using Timepix camera technology. Irregular spot shapes indicate sensitivity to grain morphology, however, resolution is smeared by beam divergence. Thus, to fully exploit available detector resolution, shorter sample-to-detector distances are currently being explored. Ongoing work combines near-field diffraction with simultaneous transmission imaging to achieve neutron diffraction contrast tomography by relating diffraction spots to grain locations.

Abstract

γ-triggered neutron time-of-flight technique was used to measure fast-neutron spectra from spontaneous fission sources using two EJ-309 liquid scintillator detectors operated in coincidence. Prompt γ-ray detection provided the timing reference for neutron energy reconstruction. Measurements were performed using bare ²⁴⁴Cm and ²⁵²Cf sources, together with a moderated ²⁵²Cf configuration to investigate scattering effects. Time-of-flight spectra were reconstructed into neutron energy distributions with corrections for detector efficiency and the non-linear time–energy relationship, supported by GEANT4 detector-response simulations. The reconstructed spectra were fitted using Maxwellian and Watt functions. Extracted Maxwellian temperatures were 1.89 MeV for bare ²⁵²Cf, 1.41–1.51 MeV for moderated ²⁵²Cf, and 1.48 MeV for ²⁴⁴Cm, demonstrating the expected spectral softening caused by moderation. Although systematic deviations from literature values were observed due to detector threshold and efficiency limitations, the method successfully resolved relative differences between source configurations. The results demonstrate the suitability of γ-triggered nToF spectrometry for comparative neutron spectral characterisation.

Abstract

Quantitative evaluation of radioactive contamination is essential for nuclear decommissioning; however, conventional survey methods provide limited spatial information, and conventional Compton cameras lack quantitative imaging capability due to their non-unique source reconstruction, in which the source position spreads into a cone. In this work, we investigate the applicability of an Electron-Tracking Compton Camera (ETCC) [1] to quantitative gamma-ray imaging in a decommissioning environment. The ETCC consists of a gaseous Time Projection Chamber (TPC) as the scatterer and a pixel scintillator array as the absorber. By reconstructing recoil electron tracks in the TPC, the ETCC uniquely solves the Compton kinematics, enabling a one-to-one correspondence between the source direction and the reconstructed image, in contrast to conventional Compton cameras. Measurements were conducted at the Prototype Advanced Thermal Reactor "FUGEN," currently under decommissioning. A ⁶⁰Co hot spot with a dose rate of approximately 1 μSv/h was successfully identified and imaged, and the dose rate estimated from the ETCC data was consistent with that obtained from a survey meter. In addition, weak ⁶⁰Co contamination at approximately 0.08 μSv/h, close to the background level and below the sensitivity limit of conventional survey meters, was visualized through direction-resolved analysis. These results demonstrate that the ETCC enables quantitative and sensitive imaging of radioactive contamination and can complement conventional survey methods, with potential to improve the efficiency of contamination assessment and clearance verification in nuclear decommissioning.