Scintillation Light Research Articles

Novel method to study saturation of silicon photomultiplier in scintillation detector

Signal saturation in the Silicon PhotoMultiplier (SiPM) often causes a serious problem in using a detector equipped with SiPMs for scintillator readout. Conventionally, SiPM signal saturation is measured through direct injection of visible light pulses to the SiPM. However, the method works poorly with the scintillation detector because the effects of the time constant of the emission of scintillation light are not included. Here, we present a novel method to measure the precise degree of SiPM signal saturation in scintillation detectors. The key difference from the conventional method is to use UV light pulses, as opposed to visible light ones, to inject and excite scintillation light in the detector. It allows us to directly measure the degree of saturation in situ taking into account all the major effects in the detector, such as the time constant of the scintillation emission. We also develop a new model for SiPM signal saturation and validate it with the measured degree of saturation with the above-mentioned new method.

DARWIN/XLZD: A future xenon observatory for dark matter and other rare interactions

The DARWIN/XLZD experiment is a next-generation dark matter detector with a multi-ten-ton liquid xenon time projection chamber at its core. Its principal goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until interactions of astrophysical neutrinos will become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the liquid xenon target will be observed by VUV-sensitive, ultra-low background photosensors. Besides its excellent sensitivity to WIMPs with masses above ∼5 GeV, such a detector with its large mass, low-energy threshold and ultra-low background level will also be sensitive to other rare interactions, and in particular also to bosonic dark matter candidates with masses at the keV-scale. We present the detector concept, discuss the main sources of backgrounds, the technological challenges and some of the ongoing detector design and R&D efforts, as well as the large-scale demonstrators. We end by discussing the sensitivity to particle dark matter interactions.

A novel cryogenic VUV spectrofluorometer for the characterization of wavelength shifters

We present a novel cryogenic VUV spectrofluorometer designed to characterize wavelength shifters (WLS) crucial for experiments based on liquid argon (LAr) scintillation light detection. Wavelength shifters like 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) or polyethylene naphthalate (PEN) are used in these experiments to shift the VUV scintillation light to the visible region. Precise knowledge of the optical properties of the WLS at liquid argon's temperature (87 K) and LAr scintillation wavelength (128 nm) is necessary to model and understand the detector response. The cryogenic VUV spectrofluorometer was commissioned to measure the emission spectra and relative wavelength shifting efficiency (WLSE) of samples between 300 K to 87 K for VUV (120 nm to 190 nm) and UV (310 nm) excitation. New mitigation techniques for surface effects on cold WLS were established. As part of this work, the TPB-based wavelength shifting reflector (WLSR) featured in the neutrinoless double-beta decay experiment LEGEND-200 was characterized. The WLSE was observed to increase by (54 ± 5) % from room temperature (RT) to 87 K. PEN installed in LEGEND-200 was also characterized, and a first measurement of the relative WLSE and emission spectrum at RT and 87 K is presented. The WLSE of amorphous PEN was found to be enhanced by at least (37 ± 4) % for excitation with 128 nm and by (52 ± 3) % for UV excitation at 87 K compared to RT.

Far UV coatings for liquid-Ar time projection chambers

Liquid Ar (LAr) and liquid Xe (LXe) time projection chambers (TPCs) are used for many applications in neutrino physics and direct dark matter searches. The performance of these detectors, particularly dual-phase ones, depends very strongly on the efficiency for detecting the far ultraviolet (FUV) scintillation light. Such detection is particularly challenging for LAr, in which the strongest scintillation feature is observed at a wavelength of 127 nm (175 nm for LXe). The current mainstream approach is covering the optical surfaces with a wavelength shifter, which absorbs de FUV light and emits at wavelengths that overlap with the optical band, where commercial devices have higher detection efficiency. This work presents coatings designed to enhance the optical properties of the detector materials and to be an alternative to the current technique. In particular, two possible coatings are proposed: narrowband and broadband FUV reflective coatings. The narrowband coatings are tuned at the FUV scintillation light. They provide a large reflectance at the design angle; additionally, these coatings are naturally transparent at longer wavelengths, which might be useful to selectively detect the wavelength of interest. Their performance is evaluated taking into account the refractive index of LAr and as a function of the angle of incidence. The same calculations are performed for an aluminium-based broadband mirror. Finally, the effect on reflectance of submerging both sorts of mirrors at liquid nitrogen temperature is presented.

Light detection and cosmic rejection in the ICARUS LArTPC at Fermilab

The ICARUS-T600 detector is a 760-ton Liquid Argon Time Projection Chamber (LArTPC) currently operating at Fermilab as the Far Detector in the Short Baseline Neutrino (SBN) program. The SBN program is composed of three LArTPCs with a central goal of testing the sterile neutrino hypothesis. After operating for 3-years in the Gran Sasso Underground Laboratory, the ICARUS detector was shipped to CERN where it was outfitted with 360 8” Photomultiplier Tubes (PMTs) for a new optical detection system. The PMT system detects fast scintillation light from charged particles interacting in the Liquid Argon, generating the trigger signal for the full detector and allows 3D reconstruction of events. Now operating at shallow depth, the detector is exposed to a high flux of cosmic rays that can fake neutrino interactions. To mitigate this effect a Cosmic Ray Tagger (CRT) and a 3-meter-thick concrete were installed. Precise timing information from both the PMT and CRT subsystems can help to identify whether an interaction originated from inside or outside of the ICARUS cryostat. This paper reviews a method for cosmogenic background reduction and timing calibration of the CRT and PMT light detection systems in ICARUS.

Particle discrimination in a NaI crystal using the COSINUS remote TES design

The COSINUS direct dark matter experiment situated at Laboratori Nazionali del Gran Sasso in Italy is set to investigate the nature of the annually modulating signal detected by the DAMA/LIBRA experiment. COSINUS has already demonstrated that sodium iodide crystals can be operated at mK temperature as cryogenic scintillating calorimeters using transition edge sensors, despite the complication of handling a hygroscopic and low melting point material. With results from a new COSINUS prototype, we show that particle discrimination on an event-by-event basis in NaI is feasible using the dual-channel readout of both phonons and scintillation light. The detector was mounted in the novel remoTES design and operated in an above-ground facility for 9.06 g·d of exposure. With a 3.7 g NaI crystal, e−/γ events could be clearly distinguished from nuclear recoils down to the nuclear recoil energy threshold of 20 keV. Published by the American Physical Society 2024

Reactor neutrino physics potentials of cryogenic pure-CsI crystal

AbstractThis paper presents a world-leading scintillation light yield among inorganic crystals measured from a 0.5 kg pure-CsI detector operated at 77 Kelvin. Scintillation photons were detected by two 2-inch Hamamatsu SiPM arrays equipped with cryogenic front-end electronics. Benefiting the light yield enhancement of pure-CsI at low temperatures and the high photon detection efficiency of SiPM, a light yield of 30.1 photoelectrons per keV energy deposit was obtained for X-rays and $$\gamma $$ γ -rays with energies from 5.9 to 59.6 keV. Instrumental and physical effects in the light yield measurement are carefully analyzed. This is the first stable cryogenic operation of kg-scale pure-CsI crystal readout by SiPM arrays at liquid nitrogen temperatures for several days. The world-leading light yield opens a door for the usage of pure-CsI crystal in several fields, particularly in detecting the coherent elastic neutrino-nucleus scattering of reactor neutrinos. The potential of using pure-CsI crystals in neutrino physics is discussed in the paper.

Digital Miniature Cathode Ray Magnetometer

In this study, we introduce the concept and construction of an innovative Digital Miniature Cathode Ray Magnetometer designed for the precise detection of magnetic fields. This device addresses several limitations inherent to magnetic probes such as D.C. offset, nonlinearity, temperature drift, sensor aging, and the need for frequent recalibration, while capable of operating in a wide range of magnetic fields. The core principle of this device involves the utilization of a charged particle beam as the sensitivity medium. The system leverages the interaction of an electron beam with a scintillator material, which then emits visible light that is captured by an imager. The emitted scintillation light is captured by a CMOS sensor. This sensor not only records the scintillation light but also accurately determines the position of the electron beam, providing invaluable spatial information crucial for magnetic field mapping. The key innovation lies in the combination of electron beam projection, CMOS imager scintillation-based detection, and digital image signal processing. By employing this synergy, the magnetometer achieves remarkable accuracy, sensitivity and dynamic range. The precise position registration enabled by the CMOS sensor further enhances the device’s utility in capturing complex magnetic field patterns, allowing for 2D field mapping. In this work, the optimization of the probe’s performance is tailored for applications related to the characterization of insertion devices in light sources, including undulators.

Measurement of the photon detection efficiency of Hamamatsu VUV4 SiPMS at cryogenic temperature

Liquid argon time projection chambers (TPC) are widely used in neutrino oscillation and dark matter experiments. Detection of scintillation light in liquid argon TPC’s is challenging because of its short wavelength, in the VUV range, and the cryogenic temperatures (∼86 K) at which the sensors must operate. Wavelength shifters (WLS) are typically needed to take advantage of the high Photon Detection Efficiency (PDE) in the visible range of most of photondetectors. The Hamamatsu VUV4 S13370–6075CN SiPMs can directly detect VUV light without the use of WLS, which main benefit is an improved PDE at these short wavelengths, but also the visible light from WLS. The manufacturer (Hamamatsu Photonics K.K.) provides a complete characterization of these devices at room temperature; however, previous studies have indicated a decrease of the PDE at cryogenic temperature for VUV light. In this work, we present the measurement of the PDE of VUV4 SiPMs at cryogenic temperature for different wavelengths in the range [270, 570] nm. A dedicated measurement at 127 nm is also shown.

Two-dimensional time-resolved scintillating sheet monitoring of proton pencil beam scanning FLASH mouse irradiations.

Dosimetry in pre-clinical FLASH studies is essential for understanding the beam delivery conditions that trigger the FLASH effect. Resolving the spatial and temporal characteristics of proton pencil beam scanning (PBS) irradiations with ultra-high dose rates (UHDR) requires a detector with high spatial and temporal resolution. To implement a novel camera-based system for time-resolved two-dimensional (2D) monitoring and apply it in vivo during pre-clinical proton PBS mouse irradiations. Time-resolved 2D beam monitoring was performed with a scintillation imaging system consisting of a 1mm thick transparent scintillating sheet, imaged by a CMOS camera. The sheet was placed in a water bath perpendicular to a horizontal PBS proton beam axis. The scintillation light was reflected through a system of mirrors and captured by the camera with 500 frames per second (fps) for UHDR and 4 fps for conventional dose rates. The raw images were background subtracted, geometrically transformed, flat field corrected, and spatially filtered. The system was used for 2D spot and field profile measurements and compared to radiochromic films. Furthermore, spot positions were measured for UHDR irradiations. The measured spot positions were compared to the planned positions and the relative instantaneous dose rate to equivalent fiber-coupled point scintillator measurements. For in vivo application, the scintillating sheet was placed 1cm upstream the right hind leg of non-anaesthetized mice submerged in the water bath. The mouse leg and sheet were both placed in a 5cm wide spread-out Bragg peak formed from the mono-energetic proton beam by a 2D range modulator. The mouse leg position within the field was identified for both conventional and FLASH irradiations. For the conventional irradiations, the mouse foot position was tracked throughout the beam delivery, which took place through repainting. For FLASH irradiations, the delivered spot positions and relative instantaneous dose rate were measured. The pixel size was 0.1mm for all measurements. The spot and field profiles measured with the scintillating sheet agreed with radiochromic films within 0.4mm. The standard deviation between measured and planned spot positions was 0.26mm and 0.35mm in the horizontal and vertical direction, respectively. The measured relative instantaneous dose rate showed a linear relation with the fiber-coupled scintillator measurements. For in vivo use, the leg position within the field varied between mice, and leg movement up to 3mm was detected during the prolonged conventional irradiations. The scintillation imaging system allowed for monitoring of UHDR proton PBS delivery in vivo with 0.1mm pixel size and 2ms temporal resolution. The feasibility of instantaneous dose rate measurements was demonstrated, and the system was used for validation of the mouse leg position within the field.

Using machine learning to separate Cherenkov and scintillation light in hybrid neutrino detector

This research investigates the separation of Cherenkov and Scintillation light signals within a simulated Water-based Liquid Scintillator (WbLS) detector, utilizing the XGBoost machine learning algorithm. The simulation data were gathered using the Rat-Pac software, which was built on the Geant4 architecture. The use of the WbLS medium has the capability to generate both Scintillation and Cherenkov light inside a single detector. To show the separation power of these two physics events, we will use the supervised learning approach. The assessment utilized a confusion matrix, classification report, and ROC curve, with the ROC curve indicating a performance result of 0.96 ± 1.2× 10-4. The research also aimed to identify essential parameters for effectively distinguishing these physics events through machine learning. For this, the study also introduced the SHAP methodology, utilizing game theory to assess feature contributions. The findings demonstrated that the number of hits has a significant effect on the trained model, while the mean hit time has a somewhat smaller impact. This research advances the utilization of AI and simulation data for accurate Cherenkov and Scintillation light separation in neutrino detectors.

Construction and evaluation of a large radiation detector for Positron Emission Tomography applications

Large arrays of pixelated scintillator potentially have application in economical construction of PET scanners. In this investigation, we constructed and evaluated a detector with an active area of 32.26 × 13.47 cm2. It is based on a 218 × 91 array of 1.4 × 1.4 × 15 mm3 LYSO elements (pitch 1.48 mm). Scintillation light is detected with a 5 × 12 array of silicon photomultipliers (SiPM) arrays. Each array consists of an 8 × 8 array of 3 × 3 mm2 (pitch 3.35 mm) SiPMs. Performance of these devices are enhanced and stabilized by cooling them. Testing revealed that the detector was able to detect 90% of the theoretically detectable 511 keV photons. The resolvability index (a measure of the ability to identify individual detector elements from background) is 0.24 ± 0.04. Additionally, the average energy resolution for the complete detector is 18.3%. These results compare well with those reported for much smaller detector modules.

Physical and luminescence properties of Ce3+ activated strontium phosphate glasses

Strontium phosphate (SrO–P2O5–Al2O3–Gd2O3) glasses with 0.05, 0.1, 0.5, and 1 mol % CeO2 were prepared by the conventional melt quenching technique. These glasses' luminescence, scintillation, and physical properties were measured and discussed in detail. The density, refractive index, and oxygen packing density of the studied glasses were increased with an increase in CeO2 concentration. At lower concentrations of CeO2, the characteristic 310 nm emission from Gd3+ and broadband emission from Ce3+ ions were obtained under X-ray excitations. The intensity of both Gd3+ and Ce3+ emission bands under 270 nm Gd3+ excitations reduced with further increase in CeO2, showing the delayed energy transfer from Gd3+ to Ce3+ ions. The integrated X-ray-induced luminescence intensity of 0.5% CeO2 glass was found to be 21% that of reference BGO crystal. For the lower concentration of CeO2, a slow decay time along with the fast Ce3+ decay was observed and disappears for higher CeO2 concentrations. The fast luminescence decay in the range of 22 ns–30 ns was observed for all the PSAG:Ce glasses, which was attributed to the lifetime of the 4f-5d transition of the Ce3+ ions. The faster decay time and reasonable scintillation light suggest the application of these glasses for radiation detector applications.

A compact detector system for simultaneous measurements of the light yield non-linearity and timing properties of scintillators

This work presents an outline of a detection system that employs the Compton spectrometer method to assess the non-linearity of scintillator light yield. A novel approach is introduced, leading to more accurate measurements through the separate determination of the intrinsic light output parameters and the non-linearity of the scintillators. Key features of this system include the use of a portable scintillation detector with three photomultiplier tubes for precise measurement of the average number of detected photoelectrons and the incorporation of recent advancements in correction techniques for accidental coincidences. The integration of digital acquisition, offline data analysis, and geometric adaptation reduces the time required to perform a measurement. The developed detector can simultaneously measure different timing properties, as well as the relative intensities following ionization excitation in a scintillator. The system’s performance is demonstrated through measurements of the light yield dependence on the deposited energy for commercially available liquid, plastic, and inorganic scintillators. Such instrumentation serves as a valuable tool in the development of novel scintillating materials, including liquid or solid organic scintillators, inorganic scintillators, and composite scintillators for electron detection, in addition to traditional X-ray or γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma$$\\end{document}-ray detection.

Optical properties of pure and Sn-doped β-Ga2O3 single crystals grown by optical float zone technique

High-quality single crystals of both pure and Sn:β-Ga2O3 single crystals weregrown using the optical floating zone technique and a comprehensive study of its luminescence and scintillation properties was carried out. The pure and Sn:β-Ga2O3 grown crystals were oriented along (100) by Laue diffraction pattern and its monoclinic structure was confirmed using a single crystal XRD. X-ray induced luminescence spectrum shows a maximum emission peak at 365 nm. The cut off wavelength was observed around 258 nm and the optical band gap was calculated to be 4.64 eV from UV–Vis-NIR transmission spectroscopy. The room temperature Raman spectra were recorded and the various vibration modes were investigated. Low temperature (10 to 300 K) and high temperature (325 to 675 K) TL measurements were carried out on X-ray irradiated crystals and its TL kinetic parameters such as activation energy (eV) and frequency factor (S) were calculated. Scintillation decay time profiles were measured for both pure and Sn-doped crystals under 137Cs γ-ray excitation. The calculated scintillation light output is 2300 Ph/5.5 Mev for Sn:β-Ga2O3 crystal under α-particle excitation from 241Am radiation source.

Through‐Space Charge‐Transfer Organogold(III) Complexes Enable High‐Performance X‐ray Scintillation and Imaging

AbstractOrganic scintillators have recently attracted growing attention for X‐ray detection in industrial and medical applications. However, these materials still face critical obstacles of low attenuation efficiency and/or inefficient triplet exciton utilization. Here we developed a new category of organogold(III) complexes, Tp‐Au‐1 and Tp‐Au‐2, through adopting a through‐space interaction motif to realize high X‐ray attenuation efficiency and efficient harvesting of triplet excitons for emission. Thanks to the efficient through‐space charge transfer process, this panel of complexes achieved higher photoluminescence quantum yield and shorter radiative lifetimes compared with the through‐bond reference complexes. Inspiringly, these organogold(III) complexes exhibited polarity‐dependent emission origins: thermally activated delayed fluorescence and/or phosphorescence. Under X‐ray irradiation, Tp‐Au‐2 manifested intense radioluminescence together with a record‐high scintillation light yield of 77,600 photons MeV−1 for organic scintillators. The resulting scintillator screens demonstrated high‐quality X‐ray imaging with >16.0 line pairs mm−1 spatial resolution, outstripping most organic and inorganic scintillators. This finding provides a feasible strategy for the design of superior organic X‐ray scintillators.

Through-Space Charge-Transfer Organogold(III) Complexes Enable High-Performance X-ray Scintillation and Imaging.

Organic scintillators have recently attracted growing attention for X-ray detection in industrial and medical applications. However, these materials still face critical obstacles of low attenuation efficiency and/or inefficient triplet exciton utilization. Here we developed a new category of organogold(III) complexes, Tp-Au-1 and Tp-Au-2, through adopting a through-space interaction motif to realize high X-ray attenuation efficiency and efficient harvesting of triplet excitons for emission. Thanks to the efficient through-space charge transfer process, this panel of complexes achieved higher photoluminescence quantum yield and shorter radiative lifetimes compared with the through-bond reference complexes. Inspiringly, these organogold(III) complexes exhibited polarity-dependent emission origins: thermally activated delayed fluorescence and/or phosphorescence. Under X-ray irradiation, Tp-Au-2 manifested intense radioluminescence together with a record-high scintillation light yield of 77,600 photons MeV-1 for organic scintillators. The resulting scintillator screens demonstrated high-quality X-ray imaging with >16.0 line pairs mm-1 spatial resolution, outstripping most organic and inorganic scintillators. This finding provides a feasible strategy for the design of superior organic X-ray scintillators.

Characteristics of Ce-doped phosphate inorganic glass scintillators for gamma- and X-ray detection

We report on the structural, photoluminescence (PL), and scintillation properties of Ce-doped P2O5–Al2O3–Cs2O–BaO glass scintillators having different Ce concentrations (1.96, 3.85, 7.41, 10.7, and 13.8 mol%) for gamma- and X-ray detection. The highest density (3.57 g/cm3) was achieved with Ce concentration of 13.8 mol%. The PL emission and X-ray-induced radioluminescence spectra showed emission peaks corresponding to the allowed transition from the Ce3+ 5d excited state to the 4f ground states. The highest scintillation light yields (approximately 2200 photons/MeV) were achieved with Ce concentrations of 7.41, 10.7, and 13.8 mol%. These light yields are higher than those previously reported for glasses containing heavy elements, such as Eu-doped SiO2–Al2O3–HfO2 (630 photons/MeV), Ce-doped P2O5–Li2O–GdI3–Al2O3–CaCO3 (1600 photons/MeV), and Ce-doped SiO2–Al2O3–BaF2–Gd2O3 (2050 photons/MeV). For all glasses, short scintillation decay times (28.5–34.0 ns) corresponding to the transition from the Ce3+ 5d excited state to the 4f ground states were observed. These results indicate that the fabricated glass with an optimal Ce concentration of 13.8 mol% is suitable for gamma- and X-ray detection.

Measurement of the photon detection efficiency of Hamamatsu VUV4 SiPMs at cryogenic temperature

Liquid argon time projection chambers play a crucial role in neutrino oscillation and dark matter experiments. Detecting scintillation light in these chambers is challenging due to the short wavelengths in the VUV range and the extremely low cryogenic temperatures (˜87 K) at which sensors operate. To take advantage of the higher photon detection efficiency (PDE) at the visible range, the use of wavelength shifters (WLS) is extended along the community. The Hamamatsu VUV4 S13370-6075CN Silicon PhotoMultiplier (SiPM) are VUV-sensitive sensors that can directly detect VUV light without the use of WLS, providing an improved PDE at these short wavelengths, and at the same time can detect the visible light from WLS if needed. The manufacturer provides a complete characterization of these sensors at room temperature. In this work we present the developed experimental setups used to measure the PDE of VUV4 SiPMs at cryogenic temperatures for different wavelengths in the range from 127 nm to 570 nm.

Evaluation of silicon and indium gallium arsenide photodiodes as direct timing detectors for pulsed x-ray systems.

Benchtop pulsed x-ray systems are commonly used to record dynamic material data on the order of nanoseconds, but pulse timing is often difficult to accurately determine. This study demonstrates that commercially available photodiodes can be used effectively for direct x-ray pulse detection without the need for visible light scintillators. X-ray pulses from four commercially available flash x-ray systems were quantified using one silicon and two indium gallium arsenide (InGaAs) photodiodes. The measured InGaAs pulse durations were strongly dependent on radiation dose in the non-linear operating regime, so the photodiodes were shielded to operate below the 2.5V non-linear regime threshold. The average pulse duration and pulse arrival time jitter of the photodiodes for each x-ray source were within several nanoseconds with the exception of two sets of measurements that were affected by low instrument sensitivity and electrical noise. These results show that InGaAs photodiodes can be used as effective and repeatable stand-alone timing diagnostics for x-ray pulses as short as 20ns or less.