Online program Overview Session: NSS-27

Abstract

Conventional measurements of neutron-induced charged-particle emission cross sections with semiconductor detectors are limited by particle energy loss in samples and stringent experimental constraints.The ¹⁴N(n, p) reaction is critical for dose evaluation in boron neutron capture therapy, as it dominates radiation dose to healthy tissue under thermal and epi-thermal neutron irradiation. High-precision cross-section data with uncertainties below 5% are indispensable for safe treatment planning, while existing datasets are currently under re-evaluation. This work aims to accurately measure the ¹⁴N(n, p) reaction cross section from 2.6×10⁻³ to 1.8 eV using a homemade sample-added scintillator detector. The scintillator consists of a base matrix, ¹⁴N-containing luminescent agent, wavelength shifter and photoinitiator. Pure scintillators and sample-added scintillator with lithium fluoride and gold powder are fabricated as active targets, attached directly on the surface of a photomultiplier tube, and aligned on the neutron beam. Experiments are carried out at the ANNRI beamline of the MLF of the JPARC with a flight length of 28.41 m. Waveform signals were recorded by a digitizer, with long-gate pulse height area, short-gate pulse shape discrimination area and time-of-flight data acquired for each event. The ¹⁴N(n, p) cross section was determined relative to the ⁶Li(n, α) reaction. Results indicates that the cross sections obtained in the present work show an overall energy dependence consistent with the expected low-energy 1/v behavior, and the measured values are consistent within uncertainty with the past experimental values and evaluated cross section data. This study demonstrates the feasibility of using self-made sample-added scintillators for measurements.

Abstract

Thermal-neutron detection in intense gamma-ray fields is required for fuel-debris monitoring and criticality safety during nuclear decommissioning. We developed co-doped Ce:LaBr₃/⁶LiBr eutectic scintillators in which the ⁶LiBr phase converts thermal neutrons through the ⁶Li(n,α)³H reaction and the Ce:LaBr₃ phase produces fast scintillation light. Building on eutectic-scintillator design concepts that enable higher Li content than stoichiometric single crystals, Sr²⁺ and Ba²⁺ co-doping were investigated to improve pulse-shape discrimination (PSD). Sr co-doping produced only limited improvement in the eutectic because Sr-rich secondary regions were formed, whereas Ba co-doping gave clearer α/γ PSD mapping. A Ce:LaBr₃/⁶LiBr detector was then evaluated in the same ²⁵²Cf-neutron/¹³⁷Cs-gamma mixed-field configuration and digital processing scheme as the optimized LiCAF:Ce detector benchmark. Neutron-source detection was demonstrated up to 5.4 Gy/h with an effective thermal-neutron sensitivity of approximately 0.3 cps/nv, indicating the potential of Ba,Ce:LaBr₃/⁶LiBr eutectics for compact neutron monitoring in decommissioning environments.

Abstract

Fast neutron detectors are essential for quantifying neutron flux in nuclear reactors, imaging the internal structure of large equipment, and detecting contraband or radioactive nuclear materials. However, no ideal technology currently enables efficient, accurate, and real-time detection of fast neutrons, which are high-energy, highly penetrating particles. There is a growing interest in hybrid organic–inorganic halide perovskites, which exhibit scintillation under X-rays, gamma rays, and fast neutrons within a single material platform. In particular, two-dimensional (2D) perovskites contain both light elements, such as hydrogen in long organic cations, which are suitable for neutron detection, and heavy elements, such as lead, which enhance X- and gamma-ray absorption [1,2].

In this presentation, I will present our approach to grow from solution by solvent evaporation, centimeter-sized single crystals of 2D perovskites, namely PEA₂PbBr₄. The optical characterizations of this single-phase, perfectly ordered crystal present two photoluminescence (PL) peaks, at 411 and 426 nm, attributed respectively to the emission from the surface and the bulk, a PLQY (Photoluminescence Quantum Yield) of 26 %, and a time decay of ≈ 3 ns. The radioluminescent measurements show a result of 20000 to 30000 Ph/MeV vs LYSO, which is better than organic scintillators, like EJ200~10000 Ph/MeV. In a second step, we will dope the reference material with cations such as Zn²⁺ or Mn²⁺ to enhance the light yield and increase the Stokes shift in order to reduce the self-absorption. We will also investigate the effects of dimensionality and halide composition to achieve a PL redshift. All synthesized materials will be evaluated under realistic neutron flux conditions, with particular attention to their stability. In parallel, their ability to discriminate between neutron and gamma radiation will also be investigated on a laboratory bench, using a ²⁵²Cf source.

Abstract

Cs₂LiLa(Br,Cl)₆:Ce (CLLBC) is a promising Elpasolite scintillator for compact gamma-ray spectroscopy and thermal-neutron detection, but the effect of Ce concentration on neutron-gamma pulse-shape discrimination (PSD) remains insufficiently quantified. In this work, CLLBC crystals with 20% Cl substitution and nominal Ce concentrations of 2%, 3%, and 4% were grown by the vertical Bridgman method. When Ce concentration increasing from 2.05% to 5.46%, the 662 keV energy resolution improved from about 3.5% to 3.2%, the relative light output increased by 9.4%, and the neutron-gamma figure of merit (FOM) increased from 1.6 to 2.0. Scintillation-decay measurements and coupled rate-transport calculations indicate that higher Ce concentration enhances energy transfer and excitation-density-dependent quenching, making neutron-like pulses more distinct from gamma-ray pulses. Continued growth optimization further enabled a 1 inch SiPM-coupled CLLBC detector that achieved 3.19% energy resolution at 662 keV and FOM = 2.37. These results demonstrate a practical route for improving CLLBC scintillators for compact mixed-field radiation detectors.

Abstract

Tl- and ⁶Li-co-doped Cs₃Cu₂I₅ crystals were grown by the Bridgman method and evaluated as thermal neutron scintillators for application in fiber-optic-coupled neutron flux monitoring systems. The grown crystals (5 × 5 × 3 mm) exhibited a light yield of approximately 140,000 ph./n_th excited thermal neutron, which is approximately 24 times higher than that of the conventional and widely used GS20 neutron scintillator. A detector was constructed by optically coupling a small crystal piece (1 × 1 × 0.2 mm) to the tip of a 20 m optical fiber. Neutron irradiation experiments were conducted at the Kyoto University Research Reactor. The neutron excited radioluminescence spectra of Tl,⁶Li doped Cs₃Cu₂I₅ were confirmed. In addition, the scintillation intensity varied linearly with neutron flux, with a coefficient of determination of R² = 0.996. These results indicate that ⁶Li- and Tl-co-doped Cs₃Cu₂I₅ is a highly promising scintillator material for real-time neutron dosimetry in high-flux environments such as boron neutron capture therapy.

Abstract

Traditionally dual-mode radiation detection requires a combination of two or more radiation detectors that work synchronously. In recent years more novel and advanced scintillation detector materials for dual-mode detection have been discovered and developed. Recent elpasolite scintillators, such as cerium doped CLYC, CLLB, and TLYC, which contain neutron sensitive materials, have been investigated as dual mode detectors. Because of the complexity of their phase diagrams, crystal growth yield, including bulk uniformity and detection performance, is lower than ideal, which eventually leads to a high final product cost. As a result, there is not a widespread interest in using these scintillators due to their high costs and scarcity although they have good detection and gamma-neutron performance. Simpler compounds like binary and ternary halides have less complicated phase diagrams due to fewer reacting compounds in the growth systems. This paper describes the efforts to grow scintillators that are capable of simultaneous neutron and gamma ray detection with lithium-doped or containing ternary halide compounds. The presence of lithium, whether it be natural or enriched ⁶Li, improves the neutron sensitivity of the compounds and allows for simultaneous detection of gamma-ray and thermal neutrons. Fast or scattered neutron detection is also possible with ternary chloride compounds. This paper presents the growth and characterization of lithium based ternary halide scintillation crystals for dual-mode neutron-gamma detection and imaging. Early results show an energy resolution about 4% (FWHM) for 662 keV gamma-rays and a primary decay constant about 800 ns. Other properties, such as melting points, transmittance and absorbance spectra, x-ray excitation optical emission spectra, as well as preliminary neutron gamma discrimination and crystal structure measurements will be presented.

Abstract

Miniature fiber-coupled organic scintillators are promising candidates for distributed neutron measurements in confined or high-radiation environments where remote placement of photodetectors and electronics is desirable. In this work, organic glass scintillator (OGS) droplets coupled to polymethyl methacrylate (PMMA) optical fibers were characterized to investigate how optical transport distance affects pulse-shape discrimination (PSD) behavior and neutron-sensitive response. Measurements were performed using direct coupling and fiber lengths up to 12 m with ²⁵²Cf and ¹³⁷Cs sources. Tail-to-total PSD was used to compare neutron and gamma-ray event populations under fixed photomultiplier operating conditions. Increasing fiber length produced substantial attenuation and broadening of both pulse populations, with the gamma-ray band degrading more rapidly than the neutron band. Low-light transport effects, coupling conditions, and threshold migration also significantly altered the PSD morphology as fiber length increased. Although low-energy calibration features were difficult to interpret due to the small scintillator geometry and probable electron escape effects, measurable neutron-sensitive PSD structure remained observable across all tested fiber lengths. These results suggest that long PMMA optical transport may preferentially suppress gamma-ray response while preserving neutron-sensitive discrimination capability relevant to neutron-signature analysis and remote neutron monitoring applications.

Abstract

Scintillators, which convert ionizing radiation into visible photons, are essential in applications ranging from high-energy physics to medical imaging. Plastic scintillators are especially attractive due to their low cost, fast response, and simple fabrication. However, their limited radiation hardness and poor geometrical adaptability restrict their use in demanding environments such as hadron therapy and real-time dosimetry. In this work, a novel nanocomposite scintillator designed for 3D printing is investigated. The material consists of a photocurable polysiloxane matrix embedding metal-halide perovskite (CsPbBr3) nanocrystals, enabling the fabrication of complex detector geometries. Beyond its manufacturability, the composite exhibits an unusual scintillation response: under alpha-particle excitation, the emitted signal shows a significantly longer decay time compared with the fast emission typical of pure perovskites. These temporal features allow effective pulse shape discrimination between gamma photons and alpha particles, representing, to the best of the authors’ knowledge, the first demonstration of this capability in hybrid perovskite-based scintillators. Preliminary optical characterization was carried out through spectrofluorimetric analysis to study the interaction between the polymer matrix and the perovskite phase, while UV--visible transmittance measurements confirmed adequate transparency for efficient light transport. Scintillation performance was then evaluated using an alpha source. Comparison with a commercial plastic scintillator benchmark highlights the potential of the proposed nanocomposite for advanced and customizable dosimetry applications, especially where flexible detector geometries and particle discrimination are required.