Wavelength Shifter Research Articles

Simulation study of the light collection efficiency and the dependency on position resolution in plastic scintillator-based muography detectors

Cosmic-ray muon imaging (muography) has been applied in various fields in recent years, in which plastic scintillators are one of the frequently selected detectors internationally. Therefore, a triangular scintillator strip based muography detection system has been proposed in the development of the μ Scattering and Transmission imaging faCility (μSTC). Before the mass production of detector units, this work studied the impacts of multiple factors on the light collection efficiency (LCE) and the position resolution (σ) of plastic scintillators. These factors include configurations of wavelength shifting (WLS) fibers, fiber grooves on scintillators, coupling optical glues and silicon photomultiplier (SiPM) readout mode. According to the simulated results, an empirical formula was proposed to quantitatively describe the relation between the LCE and σ, which has seldom been studied before. In this formula, σ reduces as a power-law function of the LCE. The SiPM readout mode (single-end or double-end output) and fiber groove treatments show no significant influence on the σ-LCE relation. LCE variations due to different factors lead to a difference in σ of less than 0.2 mm in the whole range of LCE. Accordingly, these factors are nearly equivalent in the improvement of detector position resolution. In comparison, the muon hit position reconstruction method nearly halves the σ after using angular and gap corrections. Thus, a better reconstruction method shows greater importance than the efforts made to increase LCEs. The simulation study in this work will provide good references for the construction of plastic scintillators of the μSTC platform in the near future.

Mass testing of SiPMs for the CMVD at IICHEP

A Cosmic Muon Veto Detector (CMVD) is being built around the mini-Iron Calorimeter (mini-ICAL) detector at the transit campus of the India based Neutrino Observatory, Madurai. The CMV detector will be made using extruded plastic scintillators with embedded wavelength shifting (WLS) fibres which propagate re-emitted photons of longer wavelengths to silicon photo-multipliers (SiPMs). The SiPMs detect these scintillation photons, producing electronic signals. The design goal for the cosmic muon veto efficiency of the CMV is >99.99% and fake veto rate less than 10^{-5}−5. A testing system was developed, using an LED driver, to measure the noise rate and gain of each SiPM, and thus determine its overvoltage (V_{ov}ov). This paper describes the test results and the analysed characteristics of about 3.5k SiPMs.

Performance of the new hadron blind HADES RICH in heavy ion collisions

The High Acceptance Dielectron Spectrometer (HADES) situated at GSI Darmstadt, Germany, has recently upgraded its gaseous ring imaging Cherenkov (RICH) detector. Studying the properties of the hot and dense fireballs produced in heavy ion collisions the RICH is the key component to efficiently identify electrons and positrons emitted therein. The new photon detection plane is comprised of 428 multianode photo electron multipliers (MAPMT)(Hamamatsu H12700) partly coated with p-Terphenyl as a wavelength shifter. It is operated with a gaseous C4H10 (isobutane) radiator making it essentially hadron blind for particle momenta up to approximately 2.5GeV/c. All 27392 MAPMT channels are read out by an FPGA based readout electronic scheme called DIRICH, which will also be used in other future Cherenkov detectors. The DIRICH readout allows to measure leading and trailing edges for each pixel pulse and hence time over threshold and hit arrival time down to sub-nanosecond precision. This article will discuss the key features of the upgraded HADES RICH and its performance based on a Ag+Ag run at E=1.58AGeV incident energy within the FAIR Phase-0 research program.

Optimization of WLS fiber readout for the HERD calorimeter

A novel 3-D calorimeter, composed of about 7500 LYSO cubes, is the key and crucial detector of the High Energy cosmic-Radiation Detection (HERD) facility to be installed onboard the China Space Station. Energy deposition from cosmic ray in each LYSO cube is translated by multiple wavelength shifting (WLS) fibers for multi-range data acquisition and real-time triggering.In this study, various methods of surface finish and encapsulation of the LYSO cube were investigated to optimize the amplitude from the WLS fiber end with the aim of improving the signal-to-noise ratio of Intensified scientific CMOS (IsCMOS) collection. The LYSO cube with five rough surfaces and a specular reflector achieves the maximum amplitude at the low-range fiber end, which is increased by roughly 44% compared to the polished cube with PTFE wrapping.The non-uniformity of amplitude at different positions on the LYSO cube surface was measured by X-ray and the positional correlation factor was derived for the entire cube. A simulation based on HERD CALO was conducted, which revealed that both the LYSO cube with five rough surfaces and the cube with rough bottom face exhibit superior energy resolution for electrons compared to the other two configurations.

(Invited) Microenvironment Responsiveness of Defect Photoluminescence of Locally Functionalized Single-Walled Carbon Nanotubes and Its Sensing Applications

Photoluminescence (PL) of single-walled carbon nanotubes (SWCNTs) in the near infrared (NIR) region is applicable to advanced optical applications such as bio-imaging and sensing. Local chemical functionalization (slight amount of chemical modification) of SWCNTs has been developed to introduce sp3 carbon defects in the sp2 carbon network of the tube walls for the luminescent defect formation.[1-3] The resultant locally functionalized SWCNTs (lf-SWCNTs) show defect PL (E 11* PL) with red-shifted wavelengths and increased quantum yields compared to original E 11 PL of pristine SWCNTs. For lf-SWCNTs, molecularly designed modifier molecules have enabled the defect PL wavelength modulation[4] and the sensing function creation.[5,6]Recently, we have reported the unique microenvironment responsiveness of defect PL of lf-SWCNTs; namely, the greater wavelength shifts of E 11* PL than E 11 PL by dielectric effects[7] and the PL shifting behavior modulation based on the chemical structure difference of the functionalized sites and the exciton localization effects[8] were observed. The microenvironment responsiveness of the defect PL was applied to the biological sensing application development.[9] To investigate protein detection/recognition functions of lf-SWCNTs, we introduced an avidin-biotin interaction with a selective and strong binding fashion at the functionalized sites of lf-SWCNTs. The lf-SWCNTs tethering biotin groups (lf-SWCNTs-b) were synthesized through diazonium chemistry, followed by its subsequent-modification. When neutravidin was mixed with a lf-SWCNTs-b solution, E 11* PL peak was red-shifted, indicating the higher polarity environment formation by the neutravidin adsorption on lf-SWCNTs-b. When avidin or streptavidin was used, wavelength shifting behaviors of E 11* PL of lf-SWCNTs-b were clearly changed depending on the used avidin derivatives. The results indicate the different polarity environment formation deriving from structural differences of each avidin derivative. Moreover, the detection signal enhancement was observed in a film device using lf-SWCNTs-b. Therefore, lf-SWCNTs have a high potential for development of advanced protein detection/recognition systems using NIR PL.[1] T. Shiraki et al. Acc. Chem. Res., 53, 1846 (2020). [2] S. Tretiak et al., Acc. Chem. Res., 53, 1791(2020) [3] Y. Wang et al. Nat. Rev. Chem., 3, 375 (2019). [4] T. Shiraki et al. ACS Nano, DOI: 10.1021/acsnano.2c09897 (2022). [5] T. Shiraki et al. Chem. Commun., 52, 12972 (2016). [6] S. Kruss et al, Angew. Chem. Int. Ed., 59, 17732 (2020). [7] T. Shiraki et al. Chem. Commun., 55, 3662 (2019). [8] T. Shiraki et al. J. Phys. Chem. C, 125, 12758 (2021). [9] T. Shiraki et al. Nanoscale, 14, 13090 (2022). Figure 1

Current Status of the Novel 3D SuperFGD Detector for the T2K Experiment

This paper is devoted to the current status of the novel fully active 3D (three-dimensional) fine-grained scintillator detector SuperFGD as a main part of the near off-axis detector upgrade program for the T2K experiment. The following important components related to the SuperFGD such as SuperFGD electronics and mechanics, wavelength shifting (WLS) fibers, and light emitting diode (LED) calibration system are also discussed here as well as the detector’s near future.

Optical property measurements of lithium chloride aqueous solution for a novel solar neutrino experiment

The lithium chloride aqueous solution has great potential to be the detection medium of a novel solar neutrino detector. The nuclide 7Li provides a charged-current interaction channel with a high cross-section for the MeV-scale solar electron-neutrinos, enabling measurement of the solar neutrino spectrum. This work measures the optical properties and the light yields of a saturated lithium chloride solution. After adsorption with activated carbon and recrystallization, the solution shows little absorption in the sensitive wavelength range of the bialkali photomultipliers. The attenuation length is evaluated to reach 50 meters at 430 nm. In addition to being a pure Cherenkov detector medium, a wavelength shifter, carbostyril 124, is added to the LiCl aqueous solution. The compatibility and the enhancement of the light yield are confirmed, enabling the development of a water-based Cherenkov-enhanced lithium-rich detector.

Beam Test Results of the RADiCAL—A Radiation Hard Innovative EM Calorimeter

High performance calorimetry conducted at future hadron colliders, such as the FCC-hh, poses a significant challenge for applying current detector technologies due to unprecedented beam luminosities and radiation fields. Solutions include developing scintillators that are capable of separating events at the sub-fifty picosecond level while also maintaining performance after extreme and constant neutron and ionizing radiation exposure. The RADiCAL is an approach that incorporates radiation tolerant materials in a sampling ‘shashlik’ style calorimeter configuration, using quartz capillaries filled with organic liquid or polymer-based wavelength shifters embedded in layers of tungsten plates and LYSO crystals. This novel design intends to address the Priority Research Directions (PRD) for calorimetry listed in the DOE Basic Research Needs (BRN) workshop for HEP Instrumentation. Here we report preliminary results from an experimental run at the Fermilab Test Beam Facility in June 2022. These tests demonstrate that the RADiCAL concept is capable of < 50 ps timing resolution.

Cherenkov Glass Detectors with Wavelength Shifting Fibers for Neutron Measurements

Two groups of Cherenkov glass detectors, containing six samples in total, have been produced in our laboratory with different compositions and configurations. The first group included three samples that were made of SiO2, and the other group contained three samples that were made of PbO+SiO2. All the samples were tested by using a PuBe source. Wavelength shifting (WLS) fibers were implemented in four samples (two from each group) to improve the light output of the Cherenkov detectors. Even though Cherenkov detectors have low noise due to the low-energy threshold and short decay constant (on the order of picoseconds), their light yield is low. A few hundred Cherenkov photons can be generated per mega-electron-volt. Without the WLS materials, most Cherenkov photons are likely to be absorbed within the glass sample before they can reach the photon sensor. WLS fibers do not directly increase the number of Cherenkov photons, but they can reduce the energy of Cherenkov photons and direct them toward the photon sensor. This photon energy reduction helps increase the efficiency of light collection and improves matching between photon wavelength and photon detector quantum efficiency. The objective of this work is to test Cherenkov glass detectors for the detection of neutrons by placing a 1-mm layer of Gd2O3 in front of the detectors. The focus is to increase the output light by observing the effect of the WLS fibers on the detection process with the use of different composition samples. The light output of the Cherenkov detectors was expected to increase more in the lead group than in the silicon group. Most of the Cherenkov energies are likely to be deposited within the glass sample. The approach is to direct the WLS photons to the photon sensor by allowing the energy deposition that takes place in the WLS fibers. A detailed model by Geant4 confirmed that the measured observations were reasonable. Both experimental and simulated results show an increase in light output when WLS fibers are added to the detectors.

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.

Study in the optical performance of plastic scintillator with WLS fiber

Muon veto is an important technique of many low background experiments. With the push in improving the sensitivity and statistics, the size of the detector for particle experiments has also been increasing. Therefore, there is a greater demand on the size of the muon veto system to efficiently identify muon events passing through the detector, minimizing the associated dead time of the target detector, and simultaneously fitting in the space requirements. In this paper, two designs of muon veto detectors composed of 200 cm×20 cm×2 cm plastic scintillator strip and a wavelength shifting(WLS) fiber coupled with SiPM, are tested. We use cosmic muons to examine the plastic scintillator along the length by scintillator cubes as probes and therefore measuring photoelectron numbers as a function of position. The design of layout-4 meets the needs of JUNO-TAO and is a compact and cheap candidate.

A light yield enhancement method using wavelength shifter for the STCF EMC

Super Tau-Charm Facility (STCF) is a next-generation high luminosity electron–positron collider facility and is currently one of the major options for accelerator-based particle physics experiment in China. The crystal-based electromagnetic calorimeter (EMC) with undoped CsI is a major sub-system of the STCF spectrometer. To fulfill the increasing physics requirements on measurement precision and the suffering of radiation, improving the detected light yield is an important task of STCF EMC R&D. This paper studies a “wavelength shifting in propagation” scheme for STCF EMC using the nanostructured organosilicon luminophore (NOL). The studies are performed by both Monte Carlo simulation and experimental tests. The light yield is proved to be improved by 159% in the experiment. Meanwhile, a study of the NOL’s radiation hardness is carried out to verify the reliability of the NOL. No obvious degradation in the performance is observed with the total ionization dose up to 100krad, far beyond the total radiation dose of STCF with ten years of operation.

Detection efficiency measurement and operational tests of the X-Arapuca for the first module of DUNE far detector

The Deep Underground Neutrino Experiment (DUNE) is a dual-site experiment for long-baseline neutrino oscillation studies, able to resolve the neutrino mass hierarchy and measure δ CP. DUNE will also have sensitivity to supernova neutrinos and to processes beyond the Standard Model, such as nucleon decay searches. The Far Detector (FD) will consist of four liquid argon TPC (17.5 kt total mass) with systems for the detection of charge and scintillation light produced by an ionization event. The charge detection system permits both calorimetry and position determination. In addition, the photon-detection system (PDS) enhances the detector capabilities for all DUNE physics drivers. The PDS of the first FD module consists of light collector modules placed in the inactive space between the innermost wire planes of the TPC anode. The light collectors, the so-called X-ARAPUCAS, are functionally a light trap that captures wavelength-shifted photons inside boxes with highly reflective internal surfaces where they are guided to Silicon Photo-multipliers (SiPM) by wavelength-shifting (WLS) bars. Functionality and operational tests of the X-ARAPUCAS to be installed in ProtoDUNE-SP phase II (FD DUNE prototype at the scale 1:20), as well as the measurement of their absolute detection efficiency is reported in this publication.

Conceptual design of a GEM (gas electron multiplier) based gas Cherenkov detector for measurement of 17MeV gamma rays from T(D, γ)5He in magnetic confinement fusion plasmas.

The only method for assessing the fusion power throughput of a deuterium-tritium (DT) reactor presently relies on determining the absolute number of 14MeV neutrons produced in the DT plasma. An independent method, developed and investigated during the recent DT campaign at the Joint European Torus, is based on the absolute counting of 17MeV gamma rays produced by the competing T(D, γ)5He reaction that features a very weak branching ratio (about 3-6 × 10-6) when compared to the main T(D,n)4He reaction. The state-of-the-art spectrometer used for gamma-ray measurements in magnetic confinement fusion plasmas is LaBr3(Ce) scintillator detectors, although they require significant neutron shielding to extract a relatively weak gamma-ray signal from a much more abundant neutron field. A better approach relies on a gamma-ray detector that is intrinsically insensitive to neutrons. We have advanced the design of a gamma-ray counter based on the Cherenkov effect for gamma-rays whose energy exceeds 11MeV, optimized to work in the neutron-rich environment of a steady-state, magnetically confined fusion plasma device. The gamma-rays interact with an aluminum window and extract electrons that move into the radiator emitting photons via the Cherenkov effect. Since the Cherenkov light consists of few photons (25 on average) in the far UV band (100-200nm), a pre-amplifier is required to transport the photons to the neutron-shielded location, which may be a few meters away, where the readout elements of the detector, either a silicon or standard photomultiplier tube, are placed. The present work focuses on the development of a scintillating GEM (Gas Electron Multiplier) based pre-amplifier that acts as a Cherenkov photon pre-amplifier and wavelength shifter. This paper presents the result of a set of Garfield++ simulations developed to find the optimal GEM working parameters. A photon gain of 100 is obtained by biasing a single GEM foil to 1kV.

SuperFGD prototype time resolution studies

The SuperFGD detector will be a novel and important upgrade to the ND280 near detector for both the T2K and Hyper-Kamiokande projects. The main goal of the ND280 upgrade is to reduce systematic uncertainties associated with neutrino flux and cross-section modeling for future studies of neutrino oscillations using the T2K and Hyper-Kamiokande experiments. The upgraded ND280 detector will be able to perform a full exclusive reconstruction of the final state from neutrino-nucleus interactions, including measurements of low momentum protons, pions and for the first time, event-by event measurements of neutron kinematics. Precisely understanding the time resolution is critical for the neutron energy measurements and hence an important factor in reducing the systematic uncertainties. In this paper we present the results of time resolution measurements made with the SuperFGD prototype that consists of 9216 plastic scintillator cubes (cube size is 1 cm3) readout with 1728 wavelength-shifting (WLS) fibers along the three orthogonal directions. We used data from a muon beam exposure at CERN. A time resolution of 0.97 ns was obtained for one readout channel after implementing the time calibration with a correction for time-walk effects. The time resolution improves with increasing energy deposited in a scintillator cube, improving to 0.87 ns for large pulses. Averaging two readout channels for one scintillator cube further improves the time resolution to 0.68 ns implying that signals in different channels are not synchronous. In addition the contribution from the time sampling interval of 2.5 ns is averaged as well. Most importantly, averaging time values from N channels improves the time resolution by ∼ 1/√(N). For example, averaging the time from 2 scintillator cubes with 2 fibers each improves the time resolution to 0.47 ns which is much better than the intrinsic electronics time resolution of 0.72 ns in one channel due to the 2.5 ns sampling window. This indicates that a very good time resolution should be achievable for neutrons since neutron recoils typically interact with several scintillator cubes and in addition produce larger signal amplitudes than muons. Measurements performed with a laser and a wide-bandwidth oscilloscope in which the contribution from the electronics time sampling window was removed demonstrated that the time resolution obtained with the muon beam is not far from the theoretical limit. The intrinsic time resolution of a scintillator cube and one WLS fiber is about 0.67 ns for signals of 56 photo electrons which is typical for minimum ionizing particles.

In Search for an Ionic Liquid with the Best Performance during 210Pb/210Bi Cherenkov Counting in Waters on an LS Counter.

The research presented in this paper aims to investigate the performance of several newly synthesized ionic liquids during 210Pb/210Bi detection in water on a liquid scintillation spectrometer Quantulus 1220 via Cherenkov counting. These experiments have been triggered by the recent reports that certain ionic liquids can act as wavelength shifters, thus significantly increasing the detection efficiency of Cherenkov radiation. The benefit of ionic liquid's addition to the analysed samples is reflected in the detection limit's decrement during 210Pb quantification, which is pertinent considering naturally low levels of 210Pb in aqueous samples. Firstly, it was discovered that ionic liquid, 1-butyl-3-methylimidazolium salicylate, is more efficient than the previously explored 2-hydroxypropylammonium salicylate. Consequently, the impact of a few other ionic liquids on Cherenkov counting efficiency with the same cation group (1-butyl-3-methylimidazolium benzoate, 1-butyl-3-methylimidazolium 3-hydroxybenzoate and 1-butyl-3-methylimidazolium 4-hydroxybenzoate) was also explored to test their potential influence. Molecular simulations have been carried out to reveal which structures of ionic liquids assure wavelength-shifting behavior. The obtained results confirmed that, among the investigated ones, only ionic liquids with the salicylate anion exhibited a wavelength shifting effect.

Development of a muon detector based on a plastic scintillator and WLS fibers to be used for muon tomography system

Muon tomography is a useful method for monitoring special nuclear materials (SNMs) such as spent nuclear fuel inside dry cask storage. Multiple Coulomb scattering of muons can be used to provide information about the 3-dimensional structure and atomic number(Z) of the inner materials. Tomography using muons is less affected by the shielding material and less harmful to health than other measurement methods.We developed a muon detector for muon tomography, which consists of a plastic scintillator, 64 long wavelength-shifting (WLS) fibers attached to the top of the plastic scintillator, and silicon photomultipliers (SiPMs) connected to both ends of each WLS fiber. The muon detector can acquire X and Y positions simultaneously using a position determination algorithm.The design parameters of the muon detector were optimized using DETECT2000 and Geant4 simulations, and a muon detector prototype was built based on the results. Spatial resolution measurement was performed using simulations and experiments to evaluate the feasibility of the muon detector. The experimental results were in good agreement with the simulation results. The muon detector has been confirmed for use in a muon tomography system.

NaI:Tl,6Li-PVT composite scintillator toward neutron and gamma discrimination

Efficient and affordable scintillators with the capability of neutron (n) and gamma (γ)-ray discrimination have become increasingly urgent for homeland security and radiation protection applications. In this work, a composite scintillator prototype made of NaI:Tl,6Li (NTL) single crystals and poly(vinyltoluene) (PVT) plastic scintillators was synthesized toward n and γ rays discrimination. The composite scintillator, with a size of 53 mm diameter × 30 mm height, is comprised of four 12 mm × 12 mm × 20 mm rectangular cuboid NTL crystals encapsulated in a PVT-based plastic scintillator matrix. PVT enable the scalability of scintillator to large geometries, and it also serves as light guide and wavelength shifter for NTL scintillation. The synthesized NTL-PVT composite has a high scintillation yield of 36,600 ± 4000 photons/MeV (equivalent to stand-alone NTL crystals), and a decent n and γ-ray pulse shape discrimination (PSD) capability with a figure-of-merit (FOM) of 1.2. These results highlight the feasibility of NTL-PVT composites as cost-effective scintillators with sufficient n and γ-ray detection performance.

Development of an Argon Light Source as a Calibration and Quality Control Device for Liquid Argon Light Detectors

The majority of future large-scale neutrino and dark matter experiments are based on liquid argon detectors. Since liquid argon is also a very effective scintillator, these experiments also have light detection systems. 127 nm wavelength of the liquid argon scintillation leads to the development of specialized light detectors, mostly based on wavelength shifters, and recently photodetectors sensitive to deeper UV. The effective calibration and quality control of these newly developed detectors is still a persisting problem. In order to respond to this need, we developed an argon light source which is based on plasma generation and light transfer across a MgF2 window. The light source is designed as a small, portable and easy to operate device to enable the acquisition of performance characteristics of several square meters of light detectors at once. Here we report on the development of the light source and its preliminary performance characteristics.

LYSO scintillation light test with an ultra-fast MCP-PMT

The scintillator can be seen as a wavelength shifter which converts the incident particle into a number of photons at certain wavelength. The scintillation light decay time of scintillator is measured by coupling the scintillator with the photosensitive device. With the photoelectric conversion process and waveform sampling technology, the waveform of the signal responding to the scintillation light is obtained. Through exponential fitting, we can obtain the decay time of the scintillator. Traditionally the photosensitive device used to measure the scintillation light have a rise time on the order of nanoseconds. In our experiment, an ultra-fast MCP-PMT with a rise time of 100 ps and a transit time spread of 46 ps at single-photon mode was used to be coupled with the Lu1.8Y2SiO5:Ce (LYSO) scintillator and obtain the scintillation light waveforms. The waveform obtained is not a complete scintillation pulse and the photons in one scintillation event are distinguished and becomes discrete pulses. A new method is introduced to measure the decay time of the scintillator and the result for LYSO with the new method is compared to the results measured with the dynode PMT XP2020.