Online program Overview Session: NSS-12

Abstract

High-resolution scintillator detectors achieve precise particle tracking through fine segmentation down to a few hundred micrometres, making complexity and costs prohibitive when scaling up to large volumes. We propose a change of paradigm: 3D imaging of particle interactions in an unsegmented monolithic volume of scintillator obtained by combining plenoptic imaging with a Single-Photon Avalanche Diode (SPAD) array sensor. We report the performance of the first SPAD-based plenoptic camera for particle detection, built around the SwissSPAD2 sensor. Results obtained from ⁹⁰Sr radioactive source, a point light source and a controlled two-photon-absorption setup as well as novel analytical and artificial-intelligence-driven 3D imaging techniques will be described. A simulation case study on neutrino detection demonstrates the unique potential of this approach and its scalability to medium (1 x 1 x 1 m³) and large (10 x 10 x 10 m³) scale scintillator volumes, with sub-millimeter 3D spatial resolution. A new custom SPAD array required to enhance the resolution currently under development is also presented. This work sets the path forward for a new system for high-precision particle tracking in dense volumes. Applications of the PLATON concept can also extend to medical imaging.

Abstract

Time-resolved ultrafast phenomena with hard X-rays are central to applications such as pump–probe spectroscopy, driving advances in detector and multichannel acquisition technologies. This work proposes a fully digital 3D (x–y–time) imager for hard X-rays. Key challenges include improving time and spatial resolution—often limited by pixelated approaches—and overcoming the low quantum efficiency of silicon detectors at high photon energies. To address these issues, we adopt a Separate Absorption and Multiplication Avalanche Photodiode (SAM-APD) based on III–V semiconductors. GaAs alloys, with higher atomic number and carrier mobility than silicon, enable significantly improved absorption efficiency and faster response. On the readout side, the shift toward multichannel systems and stringent constraints on power and area per channel motivate a transition from voltage-mode pixel electronics to time-based acquisition, where spatial (x, y) and temporal information are encoded in the detection time. The proposed architecture couples a large-area GaAs SAM-APD (mm-scale diameter) with two Cross Delay Lines (CDLs) and a 4-channel Field-Programmable Gate Array (FPGA)-based Time-to-Digital Converter (TDC) with 15 ps precision. The main challenges are preserving spatial coherence between the interaction point on the detector and the corresponding charge readout location on the CDL, and ensuring capacitive coupling with high signal integrity. Preliminary tests were performed using a 10 × 5 mm² p–i–n diode and laser pulses achieving a spatial precision of <100 μm r.m.s. and a temporal jitter of 68.3 ps r.m.s. Additional measurements show intensity discrimination capability with resolvable signal changes of ~1.2–1.6×. The approach offers a compact and scalable alternative to pixelated detectors, eliminating the need for advanced lithography and per-pixel readout, while relying on only four acquisition channels.

Abstract

The demand for radiation-hard 4D detectors capable of simultaneous high-precision timing and spatial resolution is driving the investigation of 4H-Silicon Carbide (4H-SiC) as a robust alternative to silicon. While 4H-SiC offers superior thermal stability and radiation tolerance, its wide bandgap and current epitaxial thickness limits necessitate the use of internal charge multiplication. This work presents an extensive performance evaluation of 4H-SiC LGADs and PN junction diodes fabricated by Onsemi on 6-inch wafers 50 μm epitaxial layer, n=5 ·10¹³  cm^-3. The devices were subjected to 23 MeV proton irradiation, covering five fluences from 1.3 ·10¹⁴ to 2 ·10¹⁵ p/cm². They have been characterized in terms of current–voltage I-V and capacitance–voltage C-V measurements. The study is complemented by ongoing Transient Current Technique (TCT) and Charge Collection Efficiency (CCE) measurements using a beta source. Furthermore, the impact of temperature (up to 200°C for I-V/C-V and 100°C for beta tests) is investigated to evaluate defect dynamics and the operational stability of 4H-SiC LGADs in extreme environments.

Abstract

The GRAiNITA project aims to develop a novel design for a next-generation calorimeter. It is an innovative approach which uses a mixture of millimeter-sized inorganic scintillating crystals (approximately 1-2 mm) dispersed within a high-density, transparent liquid. Compared to other sampling calorimeter with sensitive material of plastic scintillator, liquid argon, or silicon detector the sampling fluctuation impact on the resolution is predicted by simulation to be much smaller (<2%/sqrt{E}) due to the high density of the scintillator grains compared to the liquid and the smallness of the grains. A test beam operated in June 2024 at CERN allowed to study the performance of a small-scale GRAiNITA prototype. The light light yield was confirmed to be approximately 10 kPE/GeV and we demonstrated the feasibility of achieving sub-2% stochastic and constant terms. Since, the project has advanced significantly. This article presents the latest developments, including the design of a full-scale demonstrator module, advanced Geant4 simulations which are used to evaluate its expected performance, and detailed characterization studies scintillation properties of ZnWO$_4$ using proton beams. These efforts pave the way for the comprehensive validation of a full-scale detector.

Abstract

FLASH radiotherapy (FLASH RT), delivered at ultra-high dose rates (>40 Gy/s), has shown potential to reduce toxicity in healthy tissues while preserving tumor control. However, accurate, real-time dosimetry at such conditions remains challenging due to limitations of conventional detectors, including saturation effects and insufficient temporal resolution. In this work, silicon carbide (SiC) diodes are investigated as a promising solution for ultra-high dose rate (UHDR) dosimetry due to their high radiation hardness, fast response, and low sensitivity to saturation [1].

A 4 × 4 array of SiC diodes (1 mm diameter, 2.2 mm pitch) and a single 2.2 mm diode were tested using pulsed 7 MeV electron beams under FLASH conditions. The detectors were evaluated in terms of linearity, time response, and spatial dose measurement capabilities using a clinical reference dosimeter and radiochromic films for comparison. The single diode demonstrated excellent linearity better than 3.5% up to 10 Gy per pulse, with no evidence of saturation or radiation damage. Time-resolved measurements confirmed the capability to resolve sub-microsecond pulse structures, consistent with accelerator signals.

The SiC array prototype enabled spatially resolved dose measurements over areas up to 70 × 50 mm², producing 2D dose maps with millimeter-scale resolution under UHDR conditions. Good agreement with independent film measurements demonstrates its accuracy for beam profiling. These results highlight the feasibility of SiC-based detectors as scalable, position-sensitive dose monitors for FLASH RT [2].

Overall, this work demonstrates the potential of SiC technology for real-time, high-resolution dosimetry in FLASH radiotherapy, paving the way for future large-area detector systems and improved quality assurance in UHDR treatments.

Abstract

Ultra-high dose rate (UHDR) radiotherapy, commonly known as FLASH radio-therapy, is a revolutionary oncological approach that spares healthy tissue while preserving tumor control. Clinical translation of this method needs radiation detectors that provide real-time dosimetry under extreme dose rates, exceeding 40-100 Gy/s. Standard dosimeters, such as ionization chambers and traditional semiconductors, may face limitations like charge recombination and signal saturation in these environments. This study investigates full-inorganic metal-halide perovskites (CsPbBr₃) as viable detector material due to its high stopping power and moderately wide bandgap. We evaluated two distinct device architectures: thin-film (TF) and single-crystal (SC) detectors. The 1 μm-thick TF detectors were fabricated using radio-frequency magnetron sputtering (MS) on flexible Kapton substrates with interdigitated electrodes. SC detectors featured Schottky-Ohmic electrodes (Ti/Au and Au) deposited by DC-MS on pure commercial crystals. Characterization indicated a dominant CsPbBr3 phase, a forbidden gap of 2.32 eV, and a dark resistivity of approximately 10⁷ Ωcm. Experimental validation was performed using a 9 MeV electron beam at Centro Pisano FLASH Radiotherapy (CPFR) and a 228 MeV proton beam at APSS (Azienda Provinciali Servizi Sanitari) Trento proton-therapy center. The tests with 9MeV electron beams covered a dose-per-pulse (DPP) range of 0.1 to 5.0 Gy delivered in 4us-long pulses, while proton testing reached dose-rates of 300 Gy/s with pulse durations of 10-25ms. Both detector types demonstrated good signal linearity and showed no evidence of saturation at the highest tested intensities. Ultimately, these results confirm that CsPbBr3 perovskite detectors are suitable for real-time monitoring in both electron and proton FLASH radiotherapy.

Abstract

At CNAO, carbon-ion beams are delivered by the standard scheme which uses betatron-core extraction of a debunched beam, while RF Knock-Out (RFKO) extraction keeps the beam bunched and drives particles transversely toward extraction. To resolve the fine temporal structure of these modes beyond the 100 ms limit of standard ESA‑ABACUS readout, a High‑Rate DAQ system with 10 ns time bins was developed. The system used the LVDS outputs of 48 central channels from two ABACUS ASICs connected to a Xilinx Kintex-7 FPGA implementing custom VHDL firmware. Counts were aggregated in 10 ns windows, stored in DDR3 memory, and analyzed offline to reconstruct beam-rate waveforms and frequency components.

Tests were performed at CNAO with clinical carbon-ion beams using Betatron and RFKO extraction at four energies (115, 209, 304, and 398 MeV/u) and three intensity levels (20%, 50%, 100%). 
A CAEN DT5203 picoTDC was also used as an independent acquisition system to record leading- and trailing-edge timing information from 32 ESA-ABACUS outputs in Streaming mode. The High-Rate DAQ resolved clear differences between the two extraction modes: RFKO showed a more compact and regular bunched time structure, while Betatron extraction showed the broader temporal distribution expected from a debunched coasting beam. Fast Fourier Transform analysis of the High-Rate DAQ waveforms allowed the main accelerator RF components to be estimated with deviations below 0.25% for all tested conditions.
The DT5203 provided complementary hit‑by‑hit timing and enabled bunch‑spacing estimation with <1.5% deviations, but suffered rate saturation at high intensities.
Overall, the High‑Rate DAQ proved suitable for fine beam‑structure measurements under clinical carbon‑ion conditions, supporting accelerator tuning, particularly for RFKO operation.

Abstract

This work investigates diamond nitrogen-vacancy (NV) centers as a new class of neutron dosimetry that uses neutron-induced defect formation as the sensing mechanism rather than treating radiation damage as a failure mode. There is no device fabrication, wire connection, or charge collection as the diamond works purely as a passive dosimeter. Fast neutrons generate carbon vacancies in nitrogen-enriched diamond, followed by high-temperature annealing to form stable NV centers exhibiting characteristic photoluminescence and optically detected magnetic resonance responses. Eight nitrogen-rich diamond samples were irradiated at The Ohio State University Research Reactor, with fluence ranging from 10¹⁵ n/cm² to 10¹⁷ n/cm², and then annealed at 800 °C for a few hours.  The results demonstrated a strong linear correlation between fluorescence intensity and neutron fluence, with up to 403× fluorescence increase observed after annealing compared to control samples. The results support the feasibility of applying diamond as compact, passive, and radiation-hardened sensors for high-fluence neutron detection in nuclear fission and fusion systems. The ongoing work is also exploring the real-time sensing using a diamond quantum sensor.