Abstract
Imaging calorimetry in scintillating media for high energy physics and tomography. Development of a new detection technique combining energy and position measurements using a homogeneous scintillating medium. The system integrates Coded Aperture Masks and SiPM arrays to reconstruct 4D maps (space + time) of energy deposition. Applicable to High Energy Physics, medical imaging, and industrial tomography. Main results: 1. Prototypes of detectors using solid and liquid (cryogenic and non-cryogenic) scintillators 2. Validated reconstruction techniques with high spatial and temporal resolution 3. Demonstrated applicability in both fundamental research and applied imaging fields
Results achieved
: The PRIN 2022 project Imaging calorimetry in scintillating media for high energy physics and tomography aimed at developing an innovative optical imaging approach for scintillation detectors based on coded-aperture masks, enabling simultaneous reconstruction of the spatial distribution of scintillation light, deposited energy, and particle trajectories in homogeneous scintillators. The project combined advanced image reconstruction algorithms, detector simulations, and prototype development to assess the feasibility of this concept for applications ranging from neutrino physics to radiation detection. A major achievement of the project was the development of a highly optimized Maximum Likelihood Expectation Maximization (ML-EM) reconstruction algorithm capable of accurately reconstructing three-dimensional scintillation light distributions while preserving quantitative photon information required for calorimetry. The algorithm was implemented on GPU architectures, reducing computation time by approximately one order of magnitude compared with initial implementations and enabling realistic simulations of large-scale detector geometries. Simulations demonstrated sub-centimeter spatial resolution, few-degree angular resolution, and accurate energy reconstruction in cryogenic scintillators, identifying liquid noble gas detectors as the most promising application. The contribution of the University of Bologna focused on the experimental development of enabling technologies for cryogenic optical readout, with particular emphasis on wavelength-shifting materials compatible with liquid argon scintillation at 128 nm. Since efficient detection of vacuum-ultraviolet scintillation photons represents one of the main technological challenges for liquid noble-gas detectors, the project investigated an entirely new class of wavelength shifters based on solution-processed layered metal-halide perovskites. The activity demonstrated, for the first time within this application context, that Mn-doped two-dimensional PEA₂PbBr₄ thin films represent a promising alternative to conventional organic wavelength shifters. The pristine layered perovskite exhibits the characteristic excitonic emission around 410–420 nm but suffers from a relatively small Stokes shift, leading to significant self-absorption losses. By introducing Mn²⁺ ions into the lattice, efficient host-to-dopant energy transfer was achieved, converting the narrow excitonic emission into a broad emission centered at approximately 620 nm. This large Stokes shift strongly suppresses reabsorption while simultaneously shifting the emitted photons toward the spectral region where silicon photomultipliers exhibit their highest photon detection efficiency. An important outcome of the project was the demonstration that these perovskite wavelength shifters maintain excellent optical performance under cryogenic operating conditions. Temperature-dependent photoluminescence measurements performed between room temperature and approximately 80 K showed a substantial increase in emission intensity upon cooling, indicating enhanced radiative efficiency exactly in the temperature range relevant for liquid argon and liquid xenon detectors. Unlike many conventional wavelength-shifting materials, the perovskite films preserved both their structural integrity and optical performance after repeated thermal cycling in liquid nitrogen, with optical profilometry revealing no evidence of cracking, delamination, or morphological degradation. This remarkable thermal robustness represents a significant advantage for applications requiring repeated cryogenic operation. The long-term stability of the materials was further assessed through photostability measurements under intense pulsed ultraviolet irradiation at cryogenic temperature. No measurable photobleaching or irreversible spectral degradation was observed, demonstrating that the films can withstand the high photon fluxes expected in scintillation detectors while maintaining stable optical conversion efficiency. From a technological perspective, another important result is the intrinsic scalability of the proposed approach. Unlike vacuum-deposited inorganic coatings, the layered perovskites are solution-processable and can therefore be deposited over very large areas using low-cost fabrication techniques, making them particularly attractive for future large-scale neutrino detectors and rare-event search experiments where extensive wavelength-shifting surfaces are required. Although the complete detector prototype could not be assembled within the project duration, the final integration step was successfully demonstrated by depositing the perovskite wavelength-shifting coating directly onto silicon photomultipliers, validating the compatibility of the material with the envisioned detector architecture. Overall, the project established both the theoretical framework for optical imaging calorimetry in scintillating media and the experimental feasibility of a new generation of cryogenic wavelength shifters based on layered perovskites. These results provide the foundation for future detector prototypes combining advanced optical reconstruction with scalable, high-performance wavelength-shifting materials, opening new perspectives for neutrino physics, rare-event searches, and cryogenic radiation detection.Project details
Unibo involved Department/s:
Dipartimento di Fisica e Astronomia "Augusto Righi"
Coordinator:
INFN-Istituto Nazionale di Fisica Nucleare(Italy)
Total Unibo Contribution: Euro (EUR) 56.620,00
Project Duration in months: 24
Start Date:
28/09/2023
End Date:
28/02/2026
