Online program Overview Session: NSS-09

Abstract

A system comprising sixteen polyvinyl toluene (PVT) scintillators is under development at the Nuclear Measurements Laboratory (CEA IRESNE) for the passive nondestructive assay of alpha-contaminated waste drums. Although PVT scintillators offer a low-cost alternative to ³He counters, their sensitivity to gamma rays and scattering cross-talk restricts the use of traditional multiplicity equations for determining spontaneous fission rates. Machine learning methods provide a viable solution to this inverse problem but require extensive training datasets, necessitating a reliable, experimentally validated numerical model. Therefore, a novel calculation scheme utilizing the FIFRELIN and PHITS Monte Carlo codes is introduced. This framework generates and transports prompt fission particles, extracting raw time-of-flight and energy deposition data. The resulting files are subsequently processed using ROOT scripts to model the detectors’ response. Specifically, the energy resolution function implemented in the simulation is derived from a ⁶⁰Co source measurement, utilizing parameters adjusted to align the simulated and experimental spectra. The full framework demonstrates good agreement with the measurement of ²⁵²Cf doubles and triples counts, enabling the generation of training data for regression models capable of accurately predicting spontaneous fission rates across various measured mock drum configurations.

Abstract

The ⁶Li-glass (GS20) Scintillator-based Anger cameras have been used for single-crystal neutron diffractometry. To expand their applications for more neutron-scattering instruments and Boron Neutron Capture Therapy (BNCT) with a neutron flux~10⁹ n/s/cm², there are urgent needs to improve the neutron detection efficiency, light yield, and neutron-gamma discrimination ratio (NGD ratio, or efficiency ratio), and to reduce the light decay lifetime of the neutron scintillator. We have developed Eu²⁺:CaF₂/⁶LiF eutectic scintillators to potentially replace the GS20 in neutron Anger cameras. In this work, we show our further endeavors in i). enhancing light yield of the eutectics in casting method; ii). improving transparency and uniformity of the eutectics in oriented growth; iii). reducing the light decay lifetime to about 4 ns via Pr³⁺ doping; iv). the enhancement in the NGD ratio using an optimized multi-layer graph filter under a self-supervised learning framework. Therefore, future Eu:CaF₂/⁶LiF eutectic neutron scintillators are expected to find wider applications not only in neutron scattering and BNCT, but also in nuclear power plants and homeland security.

Abstract

Accurate assessment of plutonium content during pyroprocessing is needed to enhance the proliferation resistance. Matrix isotopic heterogeneity, source non-uniformity, and high gamma-ray emission rate prevent the application of traditional non-destructive assay (NDA) systems and methods. We aim to develop a novel NDA system that can withstand pyroprocessing harsh environments and have consistent sensitivity and accuracy despite different fuel form factors. The proposed NDA system encompasses two system modules, a boron-coated-straw (BCS) multiplicity module and a 3D boron-coated-straw detector array (3D-BCSDA) tomography module. The multiplicity module performs multiplicity counting and provides assay observables, whereas the tomographic module reduces systematic biases by enabling geometry-aware corrections. In this work, we report the development of the multiplicity module and the 3D-BCSDA tomography module. The multiplicity module consists of six 64-straw BCS panels, with a measured neutron detection efficiency of 12.4% and die-away time of 42 μs. The tomography module is a moderated array incorporating thirty one-meter-long boron-coated straws with double-sided readout. Time delay lines and charge sharing have been implemented to enable 3D localization of the neutron interaction event. We will begin experimental testing with laboratory sources at UIUC and plutonium sources at INL to assess the system’s accuracy in real-world conditions, supporting the integration of tomographic imaging with neutron multiplicity counting for bulk plutonium assay.

Abstract

The REALPATH detector and readout platform is a pixilated scintillation detector developed for prompt gamma imaging in proton therapy. Prompt gamma imaging aims to provide online verification of proton range via the position-sensitive detection of prompt gamma rays emitted during proton treatment. Due to the high fluence of modern medical proton accelerators, the detector is designed to cope with rates of up to 1 Mcps per pixel across 512 pixels. At the same time, good spectroscopic performance at high energies in the range of 3 MeV to 6 MeV is beneficial for neutron background rejection and prompt-gamma emission analysis. To address these requirements, each LYSO pixel features an independent SiPM readout, implemented with the custom SITH (spectroscopy imaging timing hadrontherapy) ASIC. In this work, we present the experimental characterization of the first 64-channel detector module. Using a ¹³⁷Cs source, we measured an average resolution of 8.5% at 662 keV for all pixels at low rates. The high source activity allowed us to characterize the detector up to 1.9 Mcps input count rate per channel. The high-energy performance was tested with a ²⁴¹Am-Be source that provides gamma rays of 4.44 MeV. By applying a light-sharing correction and combining data from coincident events across multiple pixels, we achieved an energy resolution of 4.8% at the 4.44 MeV full-energy peak. With these characteristics, the detector may also be suited for applications beyond prompt gamma imaging that require position-resolved high-rate gamma spectroscopy.

Abstract

Conventional alpha/gamma instruments often use bulk scintillators coupled to photomultiplier or silicon-photomultiplier pulse processing, or hybrid pixel detectors optimized for timing or deposited-energy readout; compact megapixel imaging with ratiometric particle-type contrast remains less developed. A monolithic alternative is demonstrated by spin-coating a 10-µm film of ligand-stabilized CsPbBr₃ perovskite nanoparticles (PNCs) onto a vertically stacked 4.8-megapixel complementary metal-oxide-semiconductor (CMOS) image sensor containing three photodiodes per pixel. Gamma-ray interactions in the PNC layer generate green scintillation photons that are registered differentially by the top, middle, and bottom photodiodes, whereas alpha particles deposit energy primarily in the top photodiode layer. Comparing these spatially registered photodiode responses with cluster amplitude and event footprint yields ratiometric single-frame alpha/gamma signatures without an external scintillator/photomultiplier timing chain. Radiation-induced events were extracted from full-frame readout as temporally nonpersistent, 8-connected pixel clusters. Relative to the uncoated sensor, the coated detector increased gamma-candidate event yield by 10³-10⁴ in Am-241, Co-57, and Ac-225 measurements. Gamma-candidate clusters exhibited median signal-to-noise ratios of 10.9-11.0 and a median footprint of one pixel. In unfiltered Ac-225 free-path measurements, the coated sensor preserved the direct alpha-particle response while adding gamma sensitivity. These results establish a spin-coated PNC/three-photodiode stacked CMOS architecture for compact, spatially resolved, ratiometric alpha/gamma imaging.

Abstract

Scintillator-based neutron detectors have been developed at ISIS for over three decades, with ongoing research and development focused on enhancing performance and meeting increasingly demanding instrument requirements. The Endeavour programme places new demands on detector technology, particularly in achieving large-area coverage, high spatial resolution, and high counting-rate capability.
Conventional WLSF detectors are built from stacked flat scintillator screens interleaved with fibre planes. Achieving high neutron efficiency (~80% at 1.8 Å) requires four scintillator layers and two fibre planes. This work presents a novel approach to the design and manufacture of ZnS:Ag/⁶LiF wavelength-shifting fibre (WLSF) detectors, with the potential to significantly improve both performance and cost-efficiency for next-generation systems.
This concept instead exploits the increase in neutron path length by tilting the scintillator relative to the incident beam. A V-shaped strip geometry is introduced, where the angle can be tuned to control detection efficiency and fibre spacing. This design also provides optical isolation between strips, enabling parallel signal processing for neutron event identification, which significantly reduces the detector dead time.A first linear position-sensitive detector prototype was developed featuring four regions with varying fibre pitches and tilt angles. This was followed by a 2D position-sensitive detector based on the same principle. The designs and performance results from tests on ISIS instruments are presented, along with a discussion of simplified manufacturing and reduced costs.
Overall, these advancements enhance detector capability and support the continued evolution of the ISIS science programme, enabling future instrument upgrades.