Online program Overview Session: N-LT-01

Abstract

Metal halide perovskites, particularly copper halide variants, have emerged as promising scintillators owing to their large Stokes shift, high photoluminescence quantum yield (PLQY), and efficient radioluminescence. Here, we demonstrate a dioxolane-mediated reaction synthesis as a simple, scalable, and high-yield strategy for producing Cs₃Cu₂Cl₅ powders with near-complete conversion. By employing low-polarity yet water-miscible dioxolane as the reaction medium together with an aqueous H₃PO₂ additive, the solubility imbalance between the precursors inherent to low-polarity solvents is effectively addressed. This approach enables stoichiometry-controlled dissolution–precipitation under a low-polarity reaction environment and the formation of phase-pure Cs₃Cu₂Cl₅ powders with near-unity PLQY. The powders show bright green emission at ~530 nm and retain over 80% of their initial efficiency after 300 days of ambient storage without encapsulation, demonstrating remarkable intrinsic stability. Cs₃Cu₂Cl₅-based composite films deliver an ultrahigh light yield of ~98,000 photons MeV^-1, greatly surpassing that of commercial scintillators such as Gd₂O₂S and CsI:Tl, and exhibiting excellent dose linearity and long-term irradiation stability. When integrated into commercial flat-panel detectors, the Cs₃Cu₂Cl₅-based composite films successfully enabled high-quality 2D radiographic and 3D computed tomography imaging, directly verifying their compatibility with existing X-ray detection systems. This facile and efficient synthesis, together with the demonstrated device-level imaging performance, highlights Cs₃Cu₂Cl₅ as a scalable and practical candidate for next-generation X-ray scintillators.

Abstract

Halide perovskites are promising scintillator materials for radiation detection and medical imaging because of their excellent optical and scintillation properties. Since the surface quality of single-crystal scintillators strongly affects light extraction and detector performance, polishing is an essential step in scintillator fabrication. However, conventional wet polishing processes are not suitable for water-sensitive crystals such as Cs₃Cu₂I₅ (CCI). In this work, hydrophobic solvents were investigated as polishing media for water-sensitive CCI single crystals. Three hydrophobic solvents—squalane, silicone oil, and mineral oil— were used as dispersion media for 1 μm alumina abrasives, followed by toluene rinsing after polishing. Among them, squalane showed the best polishing performance, yielding the lowest surface roughness (R_q=17.29 nm), the highest transmittance of 78.21%, and the narrowest rocking-curve FWHM of 0.025°. In addition, sequential polishing in squalane using P2000 sandpaper, P4000 sandpaper, and 1 μm alumina enhanced the light yield and improved the energy resolution from 6.53% to 5.83%. These results identify squalane as a promising polishing medium for water-sensitive halide perovskite scintillators.

Abstract

Six commonly used models for neutron induced light yield in organic scintillators were fit and analyzed using measurements of a 2.54 cm diameter by 2.54 cm long right circular cylinder of EJ301D and a (5.08 cm)3 custom made cube of deuterated trans-stilbene-d12 (d-stilbene). Measured neutron energies spanned 300 keV to 2200 keV for the EJ301D scintillator and 200 keV to 2500 keV in d-stilbene. The model fits and experimental analysis methods were verified by examining the agreement between the predicted light output spectrum and the measured light output spectrum for several simulated quasi-monoenergetic neutron sources. Birks model inaccurately predicted highly quenched light yield for sub-MeV neutrons in both scintillators. The addition of a second order quenching term to the Birks model by Chou significantly improved the models accuracy, however its behavior is non-physical if extrapolated beyond the measured neutron energies. The model derived by Voltz accurately fit the measurement of both scintillators for all measured neutron energies. Further investigation into the ability to extrapolate based on these semi-empiric models would be valuable given the non-physical behavior of well-fitting models.

Abstract

Eljen plastic scintillator disks have been coated with layers of neutron sensitiser in a systematic study on the thickness of neutron detection layers. Here we discuss the impact of enhancing standard plastic scintillator (PVT) with coatings containing both lithium and boron isotopes. The application of these layers enhances the material to provide a mechanism for detecting neutron radiation. A systematic study was performed to assess the impact of sensitiser thickness on neutron detection efficiency and neutron-gamma pulse shape discrimination (PSD) performance. Samples were exposed to the mixed radiation fields of a ²⁵²Cf source, and a sample of plutonium. The results demonstrate clear neutron-gamma discrimination in sensitised samples, with measured figures of merit in excess of 3 recorded for optimised lithium-rich coatings. This is comparable performance to established dual-mode detectors. These findings show that thin, externally applied neutron-sensitising layers provide an effective route to enhancing the performance of conventional plastic scintillators. This approach may offer a low-cost means of upgrading existing detector systems in nuclear security applications.

Abstract

Cerium-doped gadolinium gallium aluminium garnet (GAGG:Ce) is a novel scintillator with excellent scintillation properties. It is suitable for use in various basic science research and applications. Because the scintillation light is quenched for charged particle detection, it is necessary to use beams from accelerators to calibrate the energy response. Measurements of energetic charged particles incident on three GAGG:Ce crystals were performed using accelerated protons, ⁴He, and ¹²C at 0^oC and 20^oC in consideration for detecting charged particles in the earth's radiation belts for space weather modeling and for deploying in dosimetry devices in ion therapy, respectively. The Birks factor which quantitatively describes the extent of quenching was deduced from the experimental data. For all three GAGG:Ce scintillators, the Birks factor decreases with the atomic number Z of the incident ions. Furthermore, less light quenching, a smaller Birks factor, was observed for GAGG:Ce at 0^oC. The quenching for the Mg-codoped GAGG:Ce which has a shorter decay time constant, was found to be less temperature dependent compared to the other two GAGG:Ce crystals.

Abstract

The temperature dependence of pulse shape discrimination performance was investigated for three commercial silicon photomultiplier technologies coupled to an EJ-276D organic scintillator. Measurements were conducted at 22 °C, 30 °C, 40 °C, and 50 °C using PuBe sources. Pulse shape discrimination was quantified using the tail-to-total ratio and figure of merit. For all devices, the figure of merit increased at 30 °C. The Broadcom device exhibited the highest performance, increasing from 1.12 at 22 °C to a maximum of 1.17 at 30 °C before decreasing to 0.76 at 50 °C. The Onsemi and Hamamatsu devices showed smaller improvements, with figure of merit values increasing from 0.86 to 0.89 and 0.84 to 0.90, respectively, between 22 °C and 30 °C. At 50 °C, all devices exhibited reduced performance due to increased silicon photomultiplier thermal noise. Temperature-dependent changes in pulse shape were observed, with increasing temperature producing faster decay and modifying the balance of prompt and delayed scintillation light, improving neutron-gamma separation at intermediate temperatures. Despite degradation at higher temperature, all devices maintained effective discrimination up to 50 °C. These results demonstrate that silicon photomultiplier-based detectors are capable of robust neutron-gamma discrimination at elevated temperatures relevant to safeguards applications.

Abstract

The HIE-ISOLDE Timing Array for Reaction Studies (HISTARS) project at CERN is developing a specialized detector system designed to measure the lifetimes of excited nuclear states. For efficient particle detection, thin square GaGG(Ce) are utilized alongside YSO due to their high density and fast scintillation properties. This work evaluates the performance of GAGG(Ce) crystals coupled with two distinct photosensors: a Hamamatsu R9779 photomultiplier tube (PMT) and an array of four silicon photomultipliers (SiPM) using a custom-designed circuit. These configurations were tested in combination with a LaBr₃(Ce) detector to facilitate coincidence measurements. Data acquisition was performed using high-speed digitizer to extract timing and energy information. This article reports on the comparative performance of both readout methods, specifically characterizing pulse shape discrimination capabilities, energy resolution, and the coincidence time resolution for alpha-gamma events. Although the energy resolution is acceptable and it has a good pulse shape discrimination capability, the measured timing limitations show that the current configuration is not ideal for the HISTARS array. These results will guide the selection of better-suited materials for high-precision timing at HIE-ISOLDE.

Abstract

Time-of-flight positron emission tomography (ToF-PET) has boosted PET image quality significantly in the last years. During its first inception it was built with cross-luminescent BaF₂ crystals, which have since been replaced by LYSO. Recently, cross-luminescence has regained popularity with new scintillators being developed. However, BaF₂ and the recently developed Cs₂ZnCl₄ could not improve on the LYSO state-of-the-art coincidence time resolution (CTR) (56 ps for 2x2x3 mm³ and 95 ps for 3x3x19 mm³). As Cs₂ZnCl₄ shows a significant Cherenkov production, we combined it with the DIGILOG approach to boost its timing performance. The DIGILOG approach segments the sensor into μSiPMs and has shown an improved timing performance for BGO due to its Cherenkov radiation and an improved SPTR. Here, we simulated a 3x3x3 mm³ and a 3x3x20 mm³ Cs₂ZnCl₄ crystal coupled to seven different μSiPM arrays. The simulation included noise factors like dark counts, cross-talk, SPAD dead time and analog noise. It was designed with a PDE of 60 % and an SPTR of 25 ps. This resulted in an improved CTR of 34+/-4 ps for an array of 20x20 μSiPMs coupled to a 3x3x3 mm³ Cs₂ZnCl₄ crystal compared to the non-segmented SiPM at 48+/-3 ps. Furthermore, for the 3x3x20 mm³ crystal, a CTR of 64+/-4 ps was reached with a 10x10 μSiPM array, while the non-segmented SiPM showed a CTR of 84+/-3 ps. The results of the segmented SiPMs improve on the LYSO state-of-the-art. Additionally, they demonstrate that the DIGILOG SiPM approach improves timing performance not just for BGO, but also for other scintillators with high Cherenkov yield, ultra-fast emission and low light yield. We also provide motivation to optimize sensors for Cs₂ZnCl₄, which could enable better timing performance than the LYSO state-of-the-art.

Abstract

Background γ-ray fields complicate neutron measurements for Nondestructive Assay (NDA) of Nuclear Materials and the next generation of advanced reactor designs, including non-light water (non-LWR) and Small Modular Reactors (SMRs). Neutron sensitive proportional counter design for high γ-ray fields often focus on optimizing ion collection time and integrating low-Z materials. In these counters, the metal cathode produces most of the Compton scattered electrons, which deposit unwanted energy and signal in the gas. The long path length for Compton electrons in the counter gas means the counter gas pressures may be optimized to increase the ratio of ion-to-electron energy deposition. Here we present gas mixture and pressure optimization for ion-to-electron energy deposition using SRIM simulations. The simulation output is then tested experimentally for its effect on neutron sensitivity in γ-ray fields between 1 R/Hr and 100 R/Hr. The ion-to-electron energy deposition ratio shows promise as an additional design consideration for neutron sensitive proportional counters in γ-ray fields, even though the experimentally measured optimum pressure of 0.5 atm for He/N₂ 95/5 is lower than the simulated optimum pressure. Future experiments with a current sensitive preamplifier (CAEN A1427) will improve neutron counting for 1 to 100 R/Hr γ-ray fields.

Abstract

Monolithic silicon CMOS Sensors represent a considerable step forward in charged particle and photon sensing, and emerge as a promising embodiment for the design of novel deep-silicon photon-counting X-ray Computed Tomography scanners . This work presents the first characterization of the ARCADIA MD3 Fully-Depleted CMOS sensors, which technology is currently the baseline for the development of innovative sensors under the framework of the EIC Pathfinder Open 1MICRON project. We report on the characterisation results using an edge-on geometry and a focused synchrotron X-ray beam at the DESY test facility. The x-rays impinge on the edge of the sensor, increasing the active sensor depth seen by the photons, which consequently improves the quantum efficiency with respect to a face-on configuration. A 37 keV focused beam incident parallel to the sensor surface allowed scans along the two directions of the sensor edge, enabling the extraction of the active sensor thickness and mechanical tilt via pixel intensity profiles. Lateral scans across pixel boundaries revealed a periodicity of the spatial modulation of mean cluster size compatible with the pixel pitch of the matrix. Taking the cluster size as the main figure of merit, the performance of the sensor was evaluated at different thresholds and multiple bias voltages in order to assess the variation in the Coulomb cone and collection dynamic. The measurements are supported by Allpix Squared Monte Carlo framework, demonstrating good consistency between the simulated and the real domain.

Abstract

High-energy physics experiments currently use Low Gain Avalanche Diodes (LGADs) as part of their time-of-flight layers to track particles, thanks to their unique temporal resolution and radiation hardness. With increasing deposited charge, the gain was observed to decrease. This gain suppression effect originates from the electrostatic field screening produced by the avalanche multiplication charge. This work investigates the resilience of the LGADs to the gain suppression by characterizing a set of detectors with different gain layer designs and thicknesses, using Transient Current Techniques.

Abstract

Mobility (μ), lifetime (τ), and mobility–lifetime product (μτ) are key metrics for semiconductor radiation detectors. Highly concentrated trapping centers or defects can distort the internal electric-field distribution, producing reduced-amplitude slow-rising charge-sensitive preamplifier pulses that degrade carrier-transit and charge-collection analyses. Although slow-rising-pulse rejection is commonly used to sharpen pulse-amplitude peaks and suppress low-amplitude tails, this work extends its use to charge-carrier transport characterization. A CdZnTeSe detector [1, 2] was characterized at room temperature under electron- and hole-transit-dominant conditions using ²⁴¹Am alpha irradiation. Pulse-shape analysis rejected slow-rising pulses for key metrics extraction. In electron-transit-dominant measurements, the fast-rising pulse events preserved the bias-dependent peak-centroid trend and yielded (μτ)_e = 5.7 × 10⁻⁴ cm²/V, μ_e = 576 cm²/V·s, and τ_e = 1.0 μs, consistent with reported values [3,4]. For hole-transit-dominant measurements, all-pulse events obscured the pulse-amplitude peak and hindered Hecht fitting. After rejection, we obtained (μτ)_h = 2.1 × 10⁻⁴ cm²/V, τ_h = 0.7 μs, comparable to reported values [5], with μ_h = 318 cm²/V·s. Using the rise-time peak as the representative transit time, both all-pulse and fast-rising-pulse events yielded similar μh values. However, when the median rise time of all-pulse events was used instead, drift velocity did not show a clear linear dependence on electric field, whereas fast-rising-pulse events retained linearity. This reflects the need for careful consideration of slow-rising components and the transit-time definition. These results show that slow-rising-pulse rejection enables reliable transport characterization beyond spectral improvement.

Abstract

We performed a high-energy proton irradiation on a cross-strip germanium detector with the goals of measuring the subsequent loss to detector spectral resolution and characterizing the effectiveness of high-temperature annealing in repairing radiation damage. This work aims to address the expected radiation damage to the Compton Spectrometer and Imager (COSI) during two-year primary mission in low-Earth orbit and evaluate methods for maintenance of spectral resolution. COSI's cross-strip germanium detectors are susceptible to damage induced by the space radiation environment. Negatively charged dislocations induced by high-energy protons trap charge carriers as they drift in the applied bias voltage. The result is a degraded hole-collection signal characterized by widened spectral lines and loss to detector spectral resolution. We irradiated a non-flight detector with a fluence of 1.1 • 10⁷ p⁺/cm² — COSI's expected exposure over prime mission (95% confidence level). After irradiation, we executed a series of high-temperature anneals aimed at physically repairing the damaged germanium. We track spectral resolution by measuring the full width half maximum (FWHM) of the 662 keV spectral line emitted by the isotope Cesium-137. We repaired widened FWHMs through high-temperature annealing to within 12% of its preradiation value, repairing to 2.97 keV compared to the original 2.67 keV. We track spectral resolution across annealing processes and characterize a timescale for repair. We find the anneal time needed to repair damage from COSI's primary mission within 1% of the spectral broadening from residual damage. We project the repair time required at 90°C to be 54 +/- 10 hours.

Abstract

This paper presents a methodology for measuring the trajectories of high-energy electrons through materials utilizing a transmission electron microscope (TEM). This novel technique is implemented to diagnose and quantify the mechanism for enhanced radiation attenuation via nanostructures. Rather than an imaging technique, the TEM is applied to radiation shielding measurements as an adaptable electron source with functionality for various beam energies, amperage, alignments, and exposure times alongside an array of precise electron detectors. By utilizing energy filtering and direct electron detection capabilities, scattering profiles are measured with minimal background contributions. This TEM method is leveraged to describe particle transport in nanostructures. Palladium nanoparticles at various monodisperse sizes are synthesized via heat injection and deposited into an epoxy matrix. The palladium epoxy nanocomposites are sectioned with an ultramicrotome to thicknesses of 70 to 1000 nm containing nanoparticle sizes of 5 to 50 nm at 20% of the total weight fraction. Scattering profile measurements at various beam energies are conducted with a variety of sample thicknesses, nanoparticle sizes, and composite fractions. Scattering profile measurements also include bulk, homogeneous palladium samples in contrast to nanomaterials composed of identical atomic percentages. Simulation of the experimental scattering profiles demonstrate an understanding for the phenomena behind nanostructured attenuation enhancement, bolstering advanced nuclear technology via a foundational description for particle transport in nanostructures.

Abstract

New generation of vertex detectors must have excellent thermo-mechanical stability, and all-silicon ladders are considered as promising solutions for future detectors. However, power consumption asymmetries between the active area and periphery can induce large temperature gradients, and in some cases a combination of air and liquid cooling will be required to achieve homogeneous thermal profiles. Microchannel cooling offers a competitive alternative to traditional cooling systems. The short thermal path between the heat load and sink gives an increased thermal evacuation performance, combined with the reduced material needed for the integrated microchannels and the reduced Coefficient of Thermal Expansion mismatch between the cooling and sensor materials to obtain an optimized cooling for radiation detectors. The development of the technology needed for the integration of the sensor with the microchannels in a single piece is an ambitious challenge, as the conditions for the microchannel formation must be compatible with the sensor, requiring the optimization of the fabrication to ensure the compatibility with CMOS processes. As a demonstrator, all-silicon ladder prototypes with integrated cooling microchannels are presented. Power consumptions for the active area and periphery of the ladders are emulated using integrated aluminum heaters. The bulk in the active area is thinned from 600 to 50 microns, and the design of the microchannels cooling circuit, integrated in the periphery of the ladder, is optimized using finite-element simulation packages. Variations of prototype ladders with different sizes, microchannel dimensions, and integrated using different wafer bonding techniques are fabricated and evaluated in detail in this work.