Scintillator Bars Research Articles

Response of the first POLAR-2 prototype to polarized beams

POLAR-2 is a dedicated gamma-ray polarimeter currently foreseen to be launched towards the China Space Station around 2027. The design of the detector is based on the legacy of its predecessor mission POLAR which was launched in 2016. POLAR-2 aims to measure the polarization of the Gamma-ray Burst prompt emission within the 30–800 keV energy range. Thanks to its high sensitivity to gamma-ray polarization, as well as its large effective area, POLAR-2 will provide the most precise measurements of this type to date. Such measurements are key to improve our understanding of the astrophysical processes responsible for Gamma-Ray Bursts. The detector consists of a segmented array of plastic scintillator bars, each one of which is read out by a Silicon PhotoMultiplier channel. The flight model of POLAR-2 will contain a total of 6400 scintillators. These are divided into 100 groups of 64 bars each, in so-called polarimeter modules. In recent years, the collaboration has designed and produced the first prototypes of these polarimeter modules and subjected these to space qualification tests. In addition, in April 2023, the first of these modules were calibrated using fully polarized gamma-ray beams at the European Synchrotron Radiation Facility (ESRF) in France. In this work, we will present the results of this calibration campaign and compare these to the simulated performance of the POLAR-2 modules. Potential improvements to the design are also discussed. Finally, the measurements are used, in combination with the verified simulation framework, to estimate the scientific performance of the full POLAR-2 detector and compare it to its predecessor.

NeuSIM4: A comprehensive GEANT4 based neutron simulation code

A new neutron SIMulation program based on the versatile GEANT4 toolkit, neuSIM4, has been developed to describe interactions of neutrons in the NE213 liquid scintillator from 0.1 to 3000 MeV. neuSIM4 is designed to accommodate complicated modern detector geometry setups with multiple scintillator detectors, each of which can be outfitted with more than one photo-multiplier. To address a broad spectrum of neutron energies, two new neutron interaction physics models, KSCIN and NxQMD, have been implemented in GEANT4. For neutrons with energy below 110 MeV, we incorporate a total of eleven neutron induced reaction channels on hydrogen and carbon nuclei, including nine carbon inelastic reaction channels, into KSCIN. Beyond 110 MeV, we implement a neutron induced reaction model, NxQMD, in GEANT4. We use its results as reference to evaluate other neutron-interaction physics models in GEANT4. We find that results from an existing cascade physics model (INCL) in GEANT4 agree very well with the results from NxQMD, and results from both codes agree with new and existing light response data. To connect KSCIN to NxQMD or INCL, we introduce a transition region where the contribution of neuSIM4 linearly decreases with corresponding increased contributions from NxQMD or INCL. To demonstrate the application of the new code, we simulate the light response and performance of a 2 × 2 m2 neutron detector wall array consisting of 25 2m-long scintillation bars. We are able to compare the predicted light response functions to the shape of the experimental response functions and calculate the efficiency of the neutron detector array for neutron energies up to 200 MeV. These simulation results will be pivotal for understanding the performance of modern neutron arrays with intricate geometries, especially in the measurements of neutron energy spectra in heavy-ion reactions.

Characterisation of plastic scintillator paddles and lightweight MWPCs for the MID subsystem of ALICE 3

The ALICE collaboration is proposing a completely new detector, ALICE 3, for operation during the LHC Runs 5 and 6. One of the ALICE 3 subsystems is the Muon IDentifier detector (MID), which has to be optimised to be efficient for the reconstruction of J/ψ at rest (muons down to p T ≈ 1.5 GeV/c) for |η| < 1.3. Given the modest particle flux expected in the MID of a few Hz/cm2, technologies like plastic scintillator bars (≈ 1 m length) equipped with wavelength-shifting fibers and silicon photomultiplier readout, and lightweight Multi-Wire Proportional Chambers (MWPCs) are under investigation. To this end, different plastic scintillator paddles and MWPCs were studied at the CERN T10 test beam facility. This paper reports on the performance of the scintillator prototypes tested at different beam momenta (from 0.5 GeV/c up to 6 GeV/c) and positions (horizontal, vertical, and angular scans). The MWPCs were tested at different momenta (from 0.5 GeV/c to 10 GeV/c) and beam intensities, their efficiency and position resolutions were verified beyond the particle rates expected with the MID in ALICE 3.

Design and performance of the front-end electronics of the charged particle detectors of PADME experiment

The PADME experiment at LNF-INFN employs positron-on-target-annihilationto search for new light particles. Crucial parts of the experiment are the chargedparticle detectors, composed of plastic scintillator bars with light transmittedby wavelength shifting fibers to silicon photomultipliers (SiPMs). The location ofthe detector — close to a turbomolecular pump, inside a vacuum tank, and exposedto 0.5 T magnetic field — has driven the design of custom modular SiPM front-endand power supply electronics. The design of the system and its performance, confirmingthe desired sub-ns resolution on the reconstructed particle flying times, is shownand discussed.

Characterization of organic glass scintillator bars and their potential for a hybrid neutron/gamma ray imaging system for proton radiotherapy range verification

For accurate and simultaneous imaging of fast neutrons (FNs) and prompt gamma rays (PGs) produced during proton therapy, the selection of a highly performant detector material is crucial. In this work, a promising candidate material known as organic glass scintillator (OGS) is characterized for this task. To this end, a precisely-timed source of neutrons and Bremsstrahlung radiation produced by the nELBE facility was used to study the light output and neutron/gamma ray pulse shape discrimination (PSD) properties of a 1 × 1 × 20 cm3 OGS bar with double-sided readout. Furthermore, the energy, timing, and depth-of-interaction (DOI) resolutions of 1 × 1 × 10 cm3 and 1 × 1 × 20 cm3 OGS and EJ-200 bars were characterized with radioactive sources. For electron-equivalent energies above 0.5 MeVee, OGS was found to have excellent PSD capabilities (figure-of-merit above 1.27), energy resolution (below 12%), coincident time resolution (below 500 ps), and DOI resolution (below 10 mm). This work establishes the data analysis methods required for hybrid FN/PG imaging using OGS, and demonstrates the materials' excellent performance for this application.

Development of the front-end electronics for a cost-effective PET-like detector system

Most detector systems used for positron emission particle tracking (PEPT) are very expensive due to the use of inorganic plastic scintillators combined with a high number of readout electronic channels. This work aims to reduce the overall cost of a PEPT-capable detector system by using large and cost-effective plastic scintillators and developing custom 2 × 2 silicon photomultiplier (SiPM) arrays, preamplifiers, and discriminators. The use of long (20mm × 20mm × 1000 mm) plastic scintillator bars read out with photodetectors only at their respective ends allows an overall smaller number of photodetectors and associated readout electronics, which in turn reduces the overall cost of the system. In addition, the development of a custom SiPM array and preamplifier allows a free selection of interconnection and readout, as most commercial producers only offer specific types of interconnections and therefore lack other connections such as serial or hybrid. Thus, several common circuit types for SiPMs and preamplifiers were tested and compared in this work, and it was found that a serial connection implemented in a hybrid interconnection for the SiPMs and an inverting preamplifier based on a high-frequency operational amplifier provided the best results for the proposed detector system. Measured with a 22Na source, the combination of SiPM array and preamplifier led to a rise time of 3.7ns and a signal amplitude of 175 mV.

Design of a mobile neutron spectrometer for the Laboratori Nazionali del Gran Sasso (LNGS)

Environmental neutrons are a source of background for rare event searches (e.g., dark matter direct detection and neutrinoless double beta decay experiments) taking place in deep underground laboratories. The overwhelming majority of these neutrons are produced in the cavern walls by means of intrinsic radioactivity of the rock and concrete. Their flux and spectrum depend on time and location. Precise knowledge of this background is necessary to devise sufficient shielding and veto mechanisms, improving the sensitivity of the neutron-susceptible underground experiments. In this report, we present the design and the expected performance of a mobile neutron detector for the LNGS underground laboratory. The detector is based on capture-gated spectroscopy technique and comprises essentially a stack of plastic scintillator bars wrapped with gadolinium foils. The extensive simulation studies demonstrate that the detector will be capable of measuring ambient neutrons at low flux levels (∼10-6 n/cm2/s) at LNGS, where the ambient gamma flux is by about 5 orders of magnitude larger.

A simulation study on spatial and time resolution for a cost-effective positron emission particle tracking system

This work is the second part of a simulation study investigating the processing of densely packed and moving granular assemblies by positron emission particle tracking (PEPT). Since medical positron emission tomography (PET) scanners commonly used for PEPT are very expensive, a PET-like detector system based on cost-effective organic plastic scintillator bars is being developed and tested for its capabilities. In this context, the spatial resolution of a resting positron source, a source moving on a freely designed model path, and a particle motion given by a discrete element method (DEM) simulation is studied using Monte Carlo simulations and the software toolkit Geant4. This not only extended the simulation and reconstruction to a moving source but also significantly improved the spatial resolution compared to previous work by adding oversampling and iteration to the reconstruction algorithm. Furthermore, in the case of a source following a trajectory developed from DEM simulations, a very good resolution of about 1 mm in all three directions and an average 3D deviation between simulated and reconstructed events of 2.3 mm could be determined. Thus, the resolution for realistic particle motion within the generic grate system (which is the test rig for further experimental studies) is well below the smallest particle size. The simulation of the dependence of the reconstruction accuracy on tracer particle location revealed a nearly constant efficiency within the entire detector system, which demonstrates that boundary effects can be neglected.

Proton irradiation of plastic scintillator bars for POLAR-2

POLAR-2, a plastic scintillator based Compton polarimeter, is currently under development and planned for a launch to the China Space Station in 2025. It is intended to shed a new light on our understanding of Gamma-Ray Bursts by performing high precision polarization measurements of their prompt emission. The instrument will be orbiting at an average altitude of 383 km with an inclination of 42° and will be subject to background radiation from cosmic rays and solar events. In this work, we tested the performance of plastic scintillation bars, EJ-200 and EJ-248M from Eljen Technology, under space-like conditions, that were chosen as possible candidates for POLAR-2. Both scintillator types were irradiated with 58 MeV protons at several doses from 1.89 Gy(corresponding to about 13 years in space for POLAR-2) up to 18.7 Gy, that goes far beyond the expected POLAR-2 life time. Their respective properties, expressed in terms of light yield, emission and absorption spectra, and activation analysis due to proton irradiation are discussed. Scintillators activation analyses showed a dominant contribution of β + decay with a typical for this process gamma-ray energy line of 511 keV.

High-resolution structural imaging of volcanoes using improved muon tracking

SUMMARY Muography is increasingly used to image the density distribution of volcanic edifices, complementing traditional geophysical tomographies. Here, we present a new muon data processing algorithm, and apply it to a new generation of scintillator-based muon detectors, to image the relative density distribution in La Soufrière de Guadeloupe volcano (Lesser Antilles, France). Our processing method iteratively searches for the best fit of each muon trajectory, accounting for all the hits registered by the detector related to the particular muon event. We test the performance of our algorithm numerically, simulating the interaction of muons with our detector and accounting for its exact assemblage including the scintillator bars and lead shielding. We find that our new data processing mitigates the impact of spurious signals coming from secondary particles, and improves the amount of successfully reconstructed events. The resulting 2-D muon images at La Soufrière have higher angular resolution than previous ones and capture the heterogeneous structure of the dome. They show density anomalies located on the summit southern region, which includes a boiling acid lake and degassing fractures, where the rock is the most porous and fumarolic activity is ongoing. This work shows the importance of combining numerical simulations of muon propagation with precise raw data processing to obtain high-quality results. It is also a first step towards fully assessing the noise contamination sources when performing muon tomography, and their correction, prior to geophysical interpretations.

High-sensitivity cardiac SPECT system design with collimator-less interspaced mosaic-patterned scintillators.

Single-photon emission computed tomography (SPECT) is an important tool for myocardial perfusion imaging (MPI). Mechanical collimators cause the resolution-sensitivity trade-off in the existing cardiac SPECT systems, which hinders fast cardiac scan capability. In this work, we propose a novel collimator-less cardiac SPECT system with interspaced mosaic-patterned scintillators, aiming to significantly improve sensitivity and reduce scan time without trading-off image resolution. We propose to assemble a collimator-less cardiac SPECT with 7 mosaic-patterned detector modules forming a half-ring geometry. The detector module consists of 10 blocks, each of which is assembled with 768 sparsely distributed scintillators with a size of 1.68 mm × 1.68 mm × 20 mm, forming a mosaic pattern in the trans-axial direction. Each scintillator bar contains 5 GAGG(Ce) scintillators and 5 optical-guide elements, forming a mosaic pattern in the axial direction. In the Monte Carlo simulations, the in-plane resolution and axial resolution are evaluated using a hot-rod phantom and 5 disk phantoms, respectively. We simulate a cardiac phantom that is placed in a water-filled cylinder and evaluate the image performance with different data acquisition time. We perform image reconstruction with the expectation-maximization algorithm using system matrices derived from the simulation of a uniform cylindrical source filling the field-of-view (FOV). Besides, a 2-D prototype system is designed to demonstrate the feasibility of the collimator-less imaging concept. In the simulation system, the sensitivity is 16.31% ± 8.85% in a 180 mm (Φ) × 100 mm (L) FOV. The 6-mm rods in the hot rod phantom and the 5-mm disks in the disk phantom are clearly separable. Satisfactory MPI image quality is achieved in the cardiac phantom study with an acquisition time of 30 s. In prototype experiments, the point sources with an 8 mm center-to-center distance are clearly separable at different positions across the FOV. The study reveals a promising approach to high-sensitivity SPECT imaging without a heavy-metal collimator. In cardiac imaging, this approach opens the way to a very fast cardiac scan with good resolution. Further works are ongoing to build a practical 3-D imaging system based on the existing design.

Upgrade of the scintillator detector for particle tracking in experiments with antiprotons

Experiments with antiprotons often require the tracking of charged particles emerging from the annihilation process. The Atomic Spectroscopy And Collisions Using Slow Antiprotons (ASACUSA) collaboration at the CERN Antiproton Decelerator (AD) used several panels of scintillating bars placed around the interaction region to detect the passage of charged pions and determine the annihilation vertex position and time. The panels were composed by extruded scintillating bars and the light was collected using WaveLength Shifting (WLS) fibers and multi-anode PhotoMultiplier Tubes (PMTs). After operating for several years, the fiber-PMT coupling quality had degraded and a major upgrade of the light readout system was planned. The PMTs will be replaced by Silicon PhotoMultipliers (SiPMs) and the front-end electronics changed accordingly. An improvement is expected in the efficiency and the uniformity of the detector response. In this contribution the commissioning of the upgrade will be described, including the results of preliminary tests with cosmic rays.

The upgrade of the ASACUSA scintillating bar detector for antiproton annihilation measurements

Antiproton annihilations on matter nuclei are usually detected by tracking the charged pions emitted in the process. A detector made of plastic scintillating bars have been built and used in the ASACUSA experiment for the last 10 years. Ageing, movements and transports caused stress on the internal mechanical structure and impacted mostly on the optical readout system which was eventually upgraded: the so far used multi-anode photo-multiplier tubes (PMTs) have been replaced by silicon photomultipliers (SiPM) and the front-end electronics had to be adapted to cope with the new signal formation. This work describes the design and operations of the upgrade, as well as the validation tests with cosmic rays.

Characterization of the basic unit in a multi-channel SiPM muography detector using cosmic muons

We report on laboratory tests performed on the basic unit of a muon detector using cosmic-ray muons. The basic unit consists of a scintillator bar with an optical fiber and two SiPM devices collecting the light signal at both ends of the fiber. The aim of the tests is to determine the temporal resolution of this base unit using the time-of-flight method also taking into account specific requirements for muography applications.

Cosmic muon tomography at the Wylfa reactor site utilising an anti-neutrino detector

An anti-neutrino detector (a prototype of VIDARR) was deployed at the Wylfa Magnox nuclear power station between 2014 and 2016. It was comprised of extruded plastic scintillating bars measuring 4 cm by 1 cm by 152 cm and utilised wavelength shifting fibres (WLS) and Multi-Pixel Photon Counters (MPPCs) to detect and quantify radiation. During deployment, the detector recorded cosmic muon events in accidental coincidence along with the anti-neutrino events. The cosmic muons produced in the upper atmosphere had their paths obscured by the power plant buildings as the cosmic muons originated behind the buildings. Cosmic muons have a significantly higher probability to be attenuated and/or absorbed by denser objects and so one-sided muographic methods were utilised to image the reactor site buildings. In order to achieve clear building outlines a control data set was taken at the University of Liverpool from 2016 to 2018 which had minimal occlusion of the cosmic muon flux by dense objects. By taking the ratio of these two data sets and using GEANT4 simulations it is possible to perform a one-sided cosmic muon tomography analysis. This analysis can be used to discern specific buildings, building heights, and features at the Wylfa reactor site including the reactor core/reactor core shielding using cosmic-ray events equivalent to that which would be seen in ∼ 3 hours of normal operation. This result demonstrates the feasibility of using cosmic muon analysis to determine a segmented detector's location with respect to surrounding buildings, assisted by aerial photography or satellite imagery.

Study of a possible silicon photomultiplier based readout of the large plastic scintillator neutron detector NeuLAND

The NeuLAND (New Large-Area Neutron Detector) plastic-scintillator-based time-of-flight detector for 0.1–1.6GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3,000 2.7m × 5 cm × 5 cm big plastic scintillator bars that are read out on each end by fast timing photomultipliers.Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a NeuLAND bar was instrumented on each end with a SiPM-based prototype of the same geometry as a 1” photomultiplier tube, including four 6 × 6mm2 SiPMs, amplifiers, high voltage supply, and microcontroller.Tests were carried out using the 35MeV electron beam from the superconducting Electron Linac for beams with high Brilliance and low Emittance (ELBE) with its picosecond-level time jitter in two different modes of operation, namely parasitic mode with one electron per bunch and single-user mode with 1–60 electrons per bunch. Acqiris fast digitisers were used for data acquisition. In addition, off-beam tests using cosmic rays and the NeuLAND data acquisition scheme have been carried out.Typical time resolutions of σ≤ 120ps were found for ≥95% efficiency for minimum ionising particles, improving on previous work at ELBE and exceeding the NeuLAND timing goal of σ< 150ps. Over a range of 10–300MeV deposited energy in the NeuLAND bar, the gain was found to deviate by ≤10% (≤20%) from linearity for 35μm (75μm) SiPM pitch, respectively, satisfactory for calorimetric use of the full NeuLAND detector. The dark rate of the prototype studied was found to be lower than the expected cosmic-ray induced background in NeuLAND.

Status of the X17 search in Montreal

At the Montreal Tandem accelerator, an experiment is being set up to measure internal pair creation from the decay of nuclear excited states using a multiwire proportional chamber and scintillator bars surrounding it from the Daphne experiment. The acceptance covers a solid angle of nearly 4π. Preamplifiers and the data acquisition hardware have been designed and tested. The 7LiF target, mounted on an Al foil and water-cooled is in a thin carbon fiber section of the beamline. The experiment will focus at first on a measurement of the internal pair creation from the 18.15 MeV state of 8Be with the aim of observing independently the X17 particle discovered by the ATOMKI experiment. Assuming the ATOMKI evaluation of the electron-pair production rate from X17, Geant4 simulation predicts observation of a clear signal after about 2 weeks of data taking with 2 μA proton beam. The IPC measurement could eventually be extended to the giant dipole resonance of 8Be, as well as to other nuclei, in particular to 10B.

Assembly and test of prototype scintillator tiles for the plastic scintillator detector of the High Energy Cosmic Radiation Detection (HERD) facility

Satellite experiments for gamma-ray and cosmic-ray detection employ plastic scintillators to discriminate charged from neutral particles in order to correctly identify gamma-rays and charged nuclei. The High Energy Cosmic Radiation Detection (HERD) facility will be among these experiments, to be installed onboard the future Chinese Space Station (CSS), to detect cosmic-rays and gamma-rays up to TeV energies. The plastic scintillator detector (PSD) will consist of scintillator tiles or bars coupled to Silicon Photomultipliers (SiPMs). To discriminate gamma-rays from charged particles and measure the ion charge up to iron nuclei a wide dynamic range is required, from few tens up to thousands of photoelectrons. We have equipped a plastic scintillator tile prototype with SiPMs produced by Hamamatsu and AdvanSiD and coupled their analog signals to the DT5550W board based on the CITIROC ASIC, produced by CAEN SpA. The CITIROC ASIC allows both the formation of a fast trigger with a configurable threshold and the digitization of analog waveforms after a preamplification and shaping stage along two paths with different gain settings. The performance of our prototype will be shown.

The PADME charged particle spectrometer

The PADME experiment aims at searching signals of a dark photon A′. This is done evaluating the final state missing mass of the process e + e − → A′γ by knowing the beam energy and measuring the four-momentum of the ordinary recoil photon. The determination of this quantity, and the capability to reject the background, are the key points for the success of the experiment.Three charged particle detectors are employed to detect the positrons that have radiated a high energy photon in the target (PVeto), electrons from the beam interactions in the target or from particles which decay to final states with electrons (EVeto), and the positrons with a relatively low energy radiation in the target (HEPVeto). All three detectors are made of plastics scintillator bars placed inside the vacuum vessel of the PADME setup. PADME Commissioning took place in 2018-2019 with the beam of the Linac of the local Beam Test Facility (BTF) and results and performance of the veto stations will be presented.

The MURAVES muon telescope: a low power consumption muon tracker for muon radiography applications

Muon Radiography or muography is based on the measurement of the absorption or scattering of cosmic muons, as they pass through the interior of large scale bodies, In particular, absorption muography has been applied to investigate the presence of hidden cavities inside the pyramids or underground, as well as the interior of volcanoes’ edifices. The MURAVES project has the challenging aim of investigating the density distribution inside the summit of Mt. Vesuvius. The information, together with that coming from gravimetric measurements, is useful as input to models, to predict how an eruption may develop. The MURAVES apparatus is a robust and low power consumption muon telescope consisting of an array of three identical and independent muon trackers, which provide in a modular way a total sensitive area of three square meters. Each tracker consists of four doublets of planes of plastic scintillator bars with orthogonal orientation, optically coupled to Silicon photomultipliers for the readout of the signal. The muon telescope has been installed on the slope of the volcano and has collected a first set of data, which are being analyzed.