Online program Overview Session: NSS-16

Abstract

Coincidence timing resolution is a critical performance parameter in time-of-flight PET and other timing sensitive applications. The timing performance of scintillation detectors is governed by intrinsic scintillator properties such as light yield, rise time, and decay constant. When detectors with different scintillation characteristics are in coincidence, these differences can distort the coincidence timing spectrum, leading to deviations from an ideal symmetric Gaussian distribution. Differences in scintillator decay constants can introduce measurable asymmetry in coincidence timing histograms. In this work, the influence of scintillator decay constant on coincidence timing histogram was investigated using several scintillators with different decay constants. The scintillators (Lu₂O₃:Yb, EPS-100 plastic scintillator, LaBr₃:Ce, LYSO:Ce, GAGG, NaI:Tl, and BGO) with dimensions of 3×3×5 mm³ mounted on identical silicon photomultipliers were placed in coincidence with a reference LYSO detector. Time difference histograms were acquired for each detector pair and quantitatively analyzed using the mean, median, and skewness of the measured distributions. The results showed nearly symmetric timing histograms for EPS-100, LaBr₃, and LYSO scintillators, whereas other scintillators exhibited increasing asymmetry. The longest tail was observed for BGO on one side of the histogram. Time difference histograms were also analytically calculated based on the arrival time distribution of the 10^th detected photon. The analytical results reproduced the main trends observed experimentally. These findings demonstrate that scintillator decay constants significantly influence the shape and asymmetry of coincidence timing histograms for non-identical detector pairs with substantially different decay constants, providing insight relevant to the design and optimization of mixed scintillator timing systems.

Abstract

Ultrafast radiation detection has been persistently limited by the formidable challenge of achieving scintillators that combine sub-nanosecond response times with high scintillation efficiency. Here, we identify atomic-level exciton confinement, achieved through the synergistic regulation of A-site organic cations in 2D perovskites, as a critical factor for breaking this performance bottleneck. The resulting (1,4-CMA)PbBr₄ crystals exhibit a rare combination of a 0.62 ns radioluminescence decay time and a high light yield of 19,730 photons/MeV, surpassing leading commercial benchmarks such as BaF₂ and LYSO:Ce. Detectors based on this material achieved a record-breaking coincidence timing resolution (CTR) of 43.3 ps for reconstruction-free Time-of-Flight Positron Emission Tomography (TOF-PET) and a high spatial resolution of 32.3 lp mm^-1 for X-ray imaging. These results establish rational lattice distortion engineering as a key principle for the development of high-performance, scalable perovskite scintillators for next-generation medical and industrial imaging.

Abstract

This study presents the fabrication and evaluation of an Optical-guiding Crystal Scintillator (OCS), a structured scintillator that achieves both high spatial resolution and high detection sensitivity in X-ray imaging. Conventional scintillators face a trade-off between these two properties, and structured scintillators have been developed to overcome this trade-off. However, simultaneously achieving fine waveguiding channels with sufficient thickness at bulk scale remains a challenge. The OCS has been proposed to address this issue [1–2]. It has regularly arrayed single-crystal scintillator cores embedded in a low-refractive-index glass cladding. Each core confines scintillation light by total internal reflection. In this work, we grew Tl-doped Cs₃Cu₂I₅ (CCI:Tl, n = 1.92) single-crystal cores through directional solidification from a melt within the 5 µm-diameter channels of a borosilicate glass plate (n = 1.47). Electron backscatter diffraction analysis of the cross-section sample confirmed that each core is a single crystal, and X-ray-excited radioluminescence showed an emission peak at 517 nm, consistent with previously reported values for CCI:Tl single crystals [3]. We evaluated spatial resolution by imaging test charts with a microfocus X-ray tube and calculating the contrast transfer function (CTF). A 500 µm-thick OCS achieved CTF = 35% at 10 lp/mm, compared with 10% for a commercial CsI:Tl columnar scintillator of the same thickness. The OCS maintained spatial resolution over a thickness range of 200 to 700 µm, whereas the commercial scintillator exhibited a sharp decline. Light yield was higher than that of the commercial CsI:Tl columnar scintillator. These results demonstrate that the OCS overcomes the conventional trade-off between spatial resolution and detection sensitivity, opening new possibilities for high-energy X-ray imaging, industrial nondestructive testing, and medical diagnostics.

Abstract

Plastic scintillators are widely used in radiation detection; however, conventional fabrication constrains detector geometry to simple shapes, limiting applicability in complex dosimetry configurations. We report the development of a geometrically flexible plastic scintillator fabricated via stereolithography (SLA) 3D printing, enabling arbitrary-geometry detector production. The formulation incorporated vinyltoluene (VT, 0–20 wt%) as an aromatic co-monomer, 2,5-diphenyloxazole (PPO, 1–2 wt%) as the primary fluorophore, 1,4-bis(2-methylstyryl)benzene (Bis-MSB, 0–0.01 wt%) as a wavelength shifter, and TPO as the photoinitiator in a commercial acrylate photopolymer host matrix. A post-print resin-dipping technique using the identical formulation improved optical transmittance from 11% to 72%. Main-effect analysis across nine formulations showed that VT at 10 wt% yields optimal optical clarity (~72% at 800 nm), while PPO at 2.0 wt% produces the highest emission intensity at 367–368 nm without concentration quenching. Self-absorption arising from PPO emission–absorption spectral overlap and a host-resin transmission cut-off at 410 nm was identified as the primary optical challenge, establishing Bis-MSB wavelength shifting as essential for light collection beyond the cut-off. Active scintillation was confirmed under Sr-90 via silicon photomultiplier (SiPM) readout, with pulse amplitude 20 times lower than EJ-200. Dosimetric characterization under Cs-137 and Co-60 with EJ-200 benchmarking will be presented.

Abstract

Organic scintillators doped with heavy metals are promising for nonproliferation work as they combine the low-Z sensitivity to neutrons with the high-Z sensitivity to photoelectric absorption of gammas. Organic glass scintillators (OGS), in particular, are easy to shape and perform almost as well as trans-stilbene in light yield, energy resolution, and pulse shape discrimination. The Detection for Nuclear Nonproliferation Group (DNNG) at the University of Michigan has already completed work on 6-mm and 12-mm cubes of the tin-loaded OGS (or Sn-OGS), finding good agreement between experimental results and MCNP simulations of reasonable fidelity. The measured energy resolution of the photopeak from the 12-mm Sn-OGS is on the order of 10% and the intrinsic efficiency is visible on a log scale, both with uniform energy-dependent trends. DNNG and RMD have just entered into an agreement to further investigate this material in the form of a 1” x 1” cylinder. We anticipate that similar basic gamma spectroscopy will reveal increased photopeak efficiency and a diminished X-ray escape peak as multiple scatters are more likely in a larger volume; however, the effect of detector volume on energy resolution is unknown. In addition, we hope to present data from Compton coincidence experiments, and begin work with gamma/neutron sources for pulse shape discrimination. This work will also be compared to MCNP simulations.

Abstract

LiquidO detectors stochastically confine scintillation and Cherenkov light around energy depositions by using media with a short optical scattering length. Wavelength-shifting fibers latticed throughout the volume capture the confined light, re-emit it, and transport it to photosensors, creating an optically segmented detector without physical optical barriers. Optical segmentation offers the prospect of effective particle identification and directional reconstruction by using the time of flight, energy deposition, and topology of events that deposit energy at multiple locations in the detector volume. A critical first step toward this capability is a position-sensitive calibration to evaluate detector homogeneity and single-scatter spatial and energy resolution. To achieve this, a four-liter LiquidO prototype detector was constructed and exposed to a collimated Cs-137 source in a tagged Compton scattering configuration. A sodium-iodide detector views the scattering region, providing spatially and energetically constrained event tagging. A Monte Carlo simulation of the experimental geometry models optical photon propagation, light collection, and photosensor noise. Initial measurements indicate a light collection of ~100 photoelectrons per MeV can be achieved in the detector center, and ongoing analysis compares measured and simulated detector responses to quantify the spatial and energy resolution.

Abstract

Future high‑luminosity collider experiments require scintillators that combine high density, ultrafast response, and strong radiation tolerance. Yb‑doped lutetium oxide (Lu₂O₃:Yb) is a promising candidate due to its 9.4 g/cm³ density, sub‑2 ns charge transfer luminescence, and light yield near 500 photons/MeV. Due to its very high melting point, Lu₂O₃ is more effectively fabricated through ceramic processing, which enables scalable production of transparent, large volume components for calorimetry and fast timing systems.

Our current effort advances two complementary ceramic routes for producing Lu₂O₃ at detector relevant sizes. In collaboration with PSU/ARL, Field‑Assisted Sintering Technology (FAST) approach is being developed to achieve monolithic parts with target dimensions of 2 × 2 × 15 cm³. In parallel, RMD is fabricating 2.5 cm‑scale cubes and thin plates using a sinter‑plus‑HIP process. Optical and scintillation measurements show that thin plates, including 1‑inch squares and 14 × 14 × 3 mm³ samples, reach light yields near 500 ph/MeV, while larger cubes currently exhibit reduced output due to limited transparency. All samples emit near 350 nm under X‑ray excitation and maintain decay times of approximately 2 ns.

In collaboration with Caltech we also produce Lu₂O₃ plates for the RaDiCAL experiment as potential replacement for LYSO, leveraging the material’s high density and ultrafast timing. The combination of fast response, radiation hardness, and scalable fabrication positions Lu₂O₃ ceramics as a strong candidate for next‑generation HEP calorimeters and timing detectors. Our results from the latest FAST‑processed Lu₂O₃ samples will also be presented at the conference.

Abstract

XEMIS2 is a liquid xenon Compton camera developed at the Subatech laboratory in Nantes, France, designed to demonstrate 3 gamma nuclear imaging on small animals for the first time. This technique exploits the three gamma rays simultaneously emitted by Scandium-44, whose combined detection constrains the emitter position in 3D, enabling a reduction of the injected activity by a factor of 100 compared to conventional Positron Emission Tomography while maintaining equivalent image quality. The detector simultaneously measures two complementary signals: scintillation light, detected by 64 photomultiplier tubes surrounding the liquid xenon active volume, and ionisation electrons, drifted by a 2 kV/cm electric field toward a pixelised anode. Accurate image reconstruction relies critically on the precise calibration of the light acquisition system. The full light calibration chain developed for XEMIS2 is presented, covering the determination of detection thresholds, the photomultiplier tubes gain calibration procedure, and the inter-channel time delay correction validated on both simulation and experimental data.