Online program Overview Session: N-LT-02

Abstract

This work presents a novel neutron detector concept aiming to provide detection efficiency and background levels equivalent to conventional ³He-based detectors, whilst boosting the maximum counting rate by several orders of magnitude. The detector retains the form-factor of a standard ³He tube and uses the same working gas mixture of ³He with admixture of CF₄ as the stopping gas. The key innovation is a fast optical readout of CF₄ prompt scintillation light using silicon photomultiplier (SiPM) sensors. The target performance is a detection efficiency equivalent to that of a standard ³He tube under identical gas filling conditions, gamma sensitivity below 10⁻⁶, and a maximum counting rate of 2 MHz/pixel, orders of magnitude improvement over existing detectors. The fast emission of CF₄ scintillation light is the enabling factor for achieving ultra-high counting rates. CF₄ exhibits a considerable photon yield, with one scintillation band in the UV and another in the visible region of the spectrum, with several thousands of photons emitted per neutron event. The efficient collection of light by the SiPMs constitutes a critical design parameter, addressed in this study through Monte Carlo optimization. The gas mixture composition is optimised to maximise the scintillation yield, and a gas purification system can be integrated into the detector to ensure long-term stability. The first experimental results of a detector prototype characterisation on a neutron beamline at the Institut Laue-Langevin (ILL) will be presented.

Abstract

Neutron contamination in advanced radiotherapy and other mixed radiation environments has become an increasing concern due to the limitations of conventional neutron detectors under intense gamma background conditions. In this work, ultra-thin 3D silicon neutron detectors specifically designed for operation in mixed radiation fields were experimentally characterized under thermal and high-energy irradiation conditions. The detectors, consisting of 20 µm-thick silicon sensors paired with ⁶LiF neutron conversion layers, were tested at the FANT thermal neutron facility and at the CERN High-Energy Reference Field (CERF). Measurements included reproducibility, angular dependence, bias voltage operation, and discrimination threshold effects using a low-voltage FPGA-based readout system. The results showed stable operation under mixed radiation fields, moderate angular dependence, and strong dependence of the response on detector bias and discrimination threshold. The ultra-thin detector architecture enabled high gamma rejection capability, enabling reliable neutron detection under intense photon background conditions. These results demonstrate the suitability of 3D ultra-thin silicon detectors for compact real-time neutron monitoring in radiation protection and medical applications.

Abstract

Scintillator-on-fiber (SOF) detectors utilizing Liglass scintillators show strong potential for neutron flux monitoring in intense radiation environments due to their high radiation hardness and fast response. Previous studies have typically employed fragmented scintillators in SOF detectors due to the difficulty of μm-scale machining. In this work, Li-glass scintillators with well-defined dimensions (1×1×0.5 to 0.25×0.25×0.5 mm³) were precisely fabricated using laser cutting, enabling a systematic investigation of the effect of scintillator size on neutron response linearity in an acceleratordriven neutron beam. With pulse-shape discrimination (PSD), the results show that neutron signals measured with scintillator sizes larger than 0.5×0.5×0.5 mm³ become blurred in the P_SP -channel scatter plot due to gamma-ray contributions and pulse pile-up at an accelerator current of 250 μA. In contrast, the smallest scintillator (0.25×0.25×0.5 mm³) maintains clear separation between neutron and gamma-ray signals. Analysis of the maximum shift error σ_m of the neutron peak centroid further indicates that this smallest scintillator effectively suppresses pileup, achieving σ_m = 0. In terms of linearity, scintillators with sizes below 0.75×0.75×0.5 mm³ yield coefficients of determination R² > 0.99 when processed using a two-dimensional fiducial cut, satisfying the requirements for neutron flux monitoring in boron neutron capture therapy (BNCT). These results demonstrate the feasibility of optimizing Li-glass scintillator size and volume in SOF detectors to achieve reliable neutron flux monitoring in BNCT applications.

Abstract

The Coded Cube Camera for Gamma-ray (C3G) is a 4π gamma-ray imager designed to estimate gamma-ray source distributions from direction-dependent detector response patterns.  In this study, we developed a 24-detector C3G consisting of 24 HR-GAGG scintillators and applied it to a plant radioisotope (RI) imaging experiment using ¹¹CO₂ gas.  In the plant RI imaging experiment, approximately 300 MBq of ¹¹CO₂ gas was supplied to a plant placed in an experimental chamber to image the transport of ¹¹C-labeled photosynthates within the plant.  During this experiment, the C3G was placed outside the chamber, and the dynamics of ¹¹CO₂ gas were continuously measured with an acquisition time of 1 s per measurement.  As a result, the inflow of the gas into the chamber was clearly visualized.  In addition, the reconstructed image intensity decreased exponentially over time.  The half-life estimated from this intensity change was 20.70 min, which was in good agreement with the known half-life of ¹¹C, 20.34 min.  These results demonstrate that the 24-detector C3G can visualize dynamic gaseous radioactive sources and estimate temporal changes in radioactivity from reconstructed image intensity.  This capability is expected to be useful for applications such as radioactive gas leakage monitoring, environmental monitoring, and nuclear security.

Abstract

Analysis of lithium ore grade is industrially significant for efficient lithium resource development and utilization, enabling improved production efficiency and reduced costs. Lithium has a large neutron absorption cross-section, and changes in lithium grade can affect the neutron lifetime, which is inversely proportional to the macroscopic absorption cross-section of ore. In this paper, a method for determining lithium grade through neutron lifetime measurements based on an e-LINAC driven photoneutron source is applied to the online analysis of lithium ore grade. Since lithium does not emit gamma rays upon neutron absorption, the neutron lifetime is measured from the time distribution of capture gamma rays induced by neutrons in the matrix elements of the medium. The feasibility of this approach has been demonstrated in experiments using various lithium nitrate solutions as simplified media. Meanwhile, the effect of neutron diffusion was investigated by simulations. The potential of neutron-induced prompt gamma analysis for reducing interference caused by variations in matrix composition is discussed. Further simulation studies and system design are in progress.

Abstract

Silicon photomultiplier (SiPM) based thermal neutron detectors have been developed at Oak Ridge National Laboratory for single crystal diffraction instruments. They have potential as good replacements for current 3He detectors on neutron reflectometers due to their high spatial resolution and fast scintillator decay time. The current software-implemented position fitting on these detectors is limited due to the processing required for the recursive least-squares algorithm. In this work, we present a fast method for determining neutron position that can be run on the Field-Programmable Gate Array (FPGA) chip that is already installed on the detector. This method compares the collected event data with pre-determined shapes stored on FPGA memory in parallel, and determines the one with the least linear error. Using this method for neutron positioning takes less time than the hardware defined dead time. Count-rate and spatial resolution results collected at the High-Flux Isotope Reactor are presented, with output count rates > 500 kcps achieved, an order of magnitude greater than the software fitting method.

Abstract

CEA Cadarache currently manages over 6,000 historical 870 L nuclear waste packages. To ensure long-term safety, French regulatory authorities require a precise characterization of each unit, specifically regarding structural integrity, fissile material mass and total activity of alpha emitters. However, the high density and volume of 870 L concrete waste packages result in significant signal attenuation, making standard passive gamma spectrometry or passive and active neutron measurements inefficient to assess the mass of nuclear materials. To maximize the signal-to-noise ratio, a specific Active Photon Interrogation (API) approach is developed inside the CINPHONIE irradiation bunker of CHICADE facility, at CEA IRESNE, Cadarache, France. This method makes use of inorganic BGO scintillators to measure high-energy delayed gamma rays from short-lived photofission products induced with a high-energy bremsstrahlung photon source, i.e., a 18 MeV LINAC. A Bayesian framework is applied to infer both the mass and the position of nuclear materials from angular acquisitions. This article is focused on testing API framework in the case where the source of the signal is located in a homogeneous environment. Based on the promising results presented here, future developments will focus on the heterogenous case.

Abstract

Gamma-ray spectroscopy is a fundamental technique for identifying radioisotopes in safety-critical applications. However, in scenarios such as nuclear accidents, high-temperature and high-radiation environments severely degrade photomultiplier tube performance. Conventional temperature compensation systems face physical voltage limits, and prior deep-learning algorithms fail because they require preserved spectral shapes. To overcome these limitations, this study presents a comprehensive strategy to enhance detector stability. First, an active high-voltage control system mitigates initial temperature-induced gain loss. Because this hardware compensation eventually reaches its physical safety limits, the system integrates a deep learning (DL) technique – bidirectional long short-term memory network – to interpret residual spectral distortions, successfully achieving accurate multi-isotope quantification up to 185 °C. Second, to address radiation-induced damage localized within the photomultiplier tube, a targeted active thermal annealing protocol was applied. Following a 1.55 kGy cumulative gamma irradiation, detector output dropped to 23.5% of its baseline. Subsequent thermal annealing of the photomultiplier tube body at 145 °C successfully restored the output to 89.4%. Ultimately, this integration of hardware, software, and active recovery lays a foundation for robust radionuclide identification under concurrent high-temperature and high-radiation constraints.

Abstract

Large cargo scanning presents a unique challenge for national security. Container size limitations pose challenges to tomographic imaging. This work proposes a new stationary, limited angle tomographic transmission scanner geometry with a unique β/γ source utilizing a pair of fixed flat panel detectors, known as Gamma Tomography (GT). A Gate 10 simulation evaluates the imaging capabilities of the scanner and explores time-of-flight (TOF) and energy discrimination as electronic collimation methods to reduce scattered radiation and improve image quality. A 600 μm thin plastic scintillator sheet encasing 100mCi of ⁶⁰Co as a near detector locally captures nearly all emitted β particles without significant γ interactions, while a far detector panel of 2 cm thick LYSO crystals captures the ~1.25 MeV energy ⁶⁰Co γ photons. Both panels were simulated as 50x80 cm with a thin, 2 cm thick, multi-material test object consisting of water, aluminum, titanium, steel, and uranium in the center of the field of view. The same simulation dataset was reconstructed with/without two separate electronic collimation schemes: valid coincidences with a 100 keV energy window around the ⁶⁰Co photopeaks, and valid coincidences with a 100 ps time resolution. Despite the short acquisition time (18sec), reconstructed images are low noise, with all objects visible above background and distinguishable. The images show attenuation coefficient under-estimation, due to object scatter. TOF and energy discrimination underestimate μ values by 25.8% and 34.3% respectively, but a large dynamic range and very high SNR in μ value is achieved for all reconstructions (SNR-water: 46, SNR-Uranium: 1369). Using time information in lieu of energy allows events scattered in the detector to be used to improve image quality and SNR, but further investigation will include achievable time resolution, panel construction, and source geometry optimization.

Abstract

SANDALS-II is an instrument being developed at the ISIS Neutron and Muon Source as a next generation diffractometer for the study of amorphous and liquid materials. This upgrade will deliver count rates up to 11 times higher than the existing SANDALS instrument and will significantly expand its scientific capabilities. This work focuses on developments of a large area scintillator detector that are essential for achieving enhanced performance. Scintillation detectors for SANDALS-II will cover a solid angle of 0.67Ω, 2.4 times greater detector coverage than the current instrument. These detectors are required to have high efficiency, particularly at higher neutron energies (short wavelengths), which is achieved using a unique design employing tiles made from alternating layers of glass and scintillator. Scintillator and glass options are explored to optimise detector and instrument performance. Different low Li and B content glasses were tested to determine the most suitable option for the instrument that provides good neutron transmission while maintaining affordability. The ratio of ZnS:Ag to ⁶LiF in the scintillator will be altered from 4:1 to 2:1 to enhance neutron absorption and therefore detection efficiency. At 30eV (0.05Å) this offers a 60% improvement in detection efficiency. The applicability of low-afterglow scintillator, ZnO:Zn/⁶LiF, for use in SANDALS-II is also explored. ZnO:Zn/⁶LiF is shown to offer a 2x increase in count rate capability over ZnS:Ag/⁶LiF, but a 6% lower neutron detection efficiency. As the reduction in efficiency using ZnO:Zn/⁶LiF is modest, this alternative scintillator offers a viable solution for the high count rate regions of SANDALS-II. With optimised glass and scintillator selection, the performance required for the upgraded instrument can be delivered. This will enable faster measurements, smaller sample studies, and time resolved experiments, making SANDALS-II a world leading disordered material neutron diffractometer.

Abstract

Silicon photomultipliers (SiPMs) are attractive photosensors for space applications because of their compact size, low cost, low operating voltage, high photon detection efficiency (PDE), and single-photon sensitivity. Their use in space applications, however, is limited by radiation-induced increases in dark count rate (DCR). This work presents the characterization and radiation tolerance study of FBK NUV-HD-MT SiPMs for the focal plane of the Terzina Cherenkov telescope onboard the NUSES mission, which will operate in a Sun-synchronous low Earth orbit (LEO) at an altitude of approximately 550 km. Devices with micro-cell sizes ranging from 25 to 50 μm were evaluated through a comprehensive characterization campaign comprising static (current-voltage), dynamic (noise and pulse-shape), and optical (photon detection efficiency) measurements to identify the sensor configuration best suited for this application. The 30 μm bare sensors were selected as the optimal solution, achieving a PDE greater than 50% at 400 nm, optical cross-talk below 2%, and a DCR below 60 kHz/mm² at 10 V overvoltage. The radiation environment was modeled using SPENVIS, and dose deposition in the focal plane was evaluated with Geant4 simulations. In parallel, radiation effects were investigated experimentally through two irradiation campaigns: a 50 MeV proton beam test and electron exposure using a Sr-90 source. Proton-induced damage produced a significant increase in leakage current and DCR, while electron-induced degradation was substantially smaller. Temperature-dependent measurements were used to extrapolate in-orbit performance and to evaluate recovery through thermal annealing. The results indicate that performing periodic annealing cycles at temperatures above 50°C can reduce the radiation-induced current by up to 40% after approximately 84 hours, helping preserve detector performance over the three-year mission.

Abstract

Many experiments rely on measuring vacuum-ultraviolet light, which is emitted in situations as diverse as scintillation in cryogenic liquid noble gases (126.8 nm in argon) and laser spectroscopy of atomic hydrogen isotopes (121.6 nm). Graphene-monolayer photodetectors offer several attractive traits: they are naturally thin, sensitive to a broad range of wavelengths, relatively simple to fabricate (including with integrated readout circuitry with the same process), and can be made on flexible substrates. We present measurements with visible and UV light down to 115 nm, including at low intensity and with fast pulses, of graphene field-effect transistors (GFETs) of various sizes up to 2 mm square fabricated on silicon. These detectors show promise for experiments from neutrinoless double beta decay searches to absolute neutrino mass measurements, as well as dark-matter searches or other VUV-detection applications.

Abstract

This work presents a real-time FPGA-based Silicon Photomultiplier (SiPM) detector emulator capable of reproducing physically accurate detector waveforms at 16-bit resolution and 2.5 GS/s analog output rate. The proposed architecture combines microscopic event simulation with a temporally quantized event-streaming model, enabling real-time waveform synthesis directly inside FPGA logic while drastically reducing bandwidth requirements compared to traditional waveform streaming approaches. The emulator separates event generation from signal shaping: software layers generate timestamped photon-hit sequences derived either from analytical distributions, Geant4 simulations, or SimSiPM microscopic detector models, while the FPGA reconstructs the analog waveform through parallel Infinite Impulse Response (IIR) filter banks implementing the SiPM transfer function; a look-ahead recursive transformation enables II = 1 operation across all banks at 156.25 MHz, consuming approximately 235 DSP48E2 slices. A multi-phase temporal quantization architecture provides 0.8 ns effective timing precision using a 156.25 MHz fabric clock and eight temporal sub-phases. Experimental validation demonstrates excellent agreement between hardware-generated waveforms and analytical as well as SimSiPM-generated references, including pile-up scenarios with overlapping scintillation events reproduced through linear superposition. The prototype operates with an end-to-end latency of approximately 83 ns.

Abstract

Reliable long-term monitoring in nuclear decommissioning facilities is hampered by the absence of permanent power infrastructure and by the radiation fields that degrade conventional electronics. We present a scintillator-photovoltaic converter that captures ambient gamma radiation and transforms it into electrical energy sufficient for periodic wireless data transmission. The converter pairs a 750 cm³ CsI(Tl) crystal with a compact GaInP photovoltaic array mounted on a single end face, following a "large absorber, minimal semiconductor" strategy.) On-site evaluation inside a contaminated-material storage building at the Fukushima Daiichi Nuclear Power Plant (~35 mSv/h) produced 273 nW per module. Two parallel modules, combined with ultra-low-power energy management and a sub-GHz radio, achieved seven autonomous transmission bursts totaling 32 packets over a 30 m link during a three-hour observation window—without any external power supply or dedicated radioactive source.

Abstract

Polarization observations in extreme ultraviolet (EUV) band have not yet been achieved because it remains technically difficult to develop wide-field EUV detectors with sufficient sensitivity. However, EUV polarization measurements are expected to provide important insights into the emission mechanisms of gamma-ray bursts (GRBs) and ultraviolet flashes associated with supernova explosions. In this study, we propose a novel EUV polarimeter based on Lobster-Eye Optics (LEO), which combines a wide field of view with polarization sensitivity. Optical simulations show that EUV reflectivity on metal surfaces strongly depends on polarization. For example, at 40 eV and an incident angle of 75° on a gold-coated mirror, the reflectivity is about 40% for p-polarization and 60% for s-polarization, respectively. This difference produces an asymmetric cross-shaped image on the focal plane detector depending on the polarization direction. To verify this principle, we developed a test chamber and conducted a synchrotron radiation experiment using a gold-coated mirror and a microchannel plate (MCP) detector. By rotating the mirror around the beam axis, we measured the modulation of the MCP count rate and evaluated the detector modulation factor. The experimental results are presented and discussed in this paper.