Wavelength Shifter Research Articles

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.

Study of Light Production With A Fifty Liter Liquid Argon TPC

The Deep Underground Neutrino Experiment (DUNE) is the next very large scale neutrino science and proton decay experiment. DUNE will consist of large-scale near and far detectors. The core elements of these detector systems are liquid argon Time Projection Chambers (LAr TPCs) and light readout systems. Two prototype far detectors were built and operated at CERN Neutrino Platform and extensive developments are underway for improved and upgraded detectors. In order to evaluate various design alternatives and validate new concepts of light readout related to large-scale LAr detectors, we have performed several experiments with a fifty liter liquid argon TPC at CERN. Among the long list of configurations we probed, study of various wavelength shifters, operation in dual phase mode and Xe and N2 doping under different scenarios can be listed. Here we report on the details of the various test campaigns and discuss our findings and their impact on the design and operational parameters.

Comparative Study between Fabricated Plastic Scintillator and Existing Product for Gamma Detection

A plastic scintillator with an injection method has been developed for a gamma radiation detector. The scintillator was made from the main matrix of polystyrene (PS) pellets with the addition of primary dopant PTP (para-terphenyl) 1.5% wt and secondary dopant as wavelength shifter (WLS) POPOP (1,4-bis [2- (phenyloxazolyl) )] - benzene) 0.01 - 0.05% wt. The mixture of pellets and dopants was fed to the extruder machine to obtain scintillating pellets and then referred to the machine to obtain a 3 mm thin plate plastic scintillator. The evaluation of absorption using a spectrophotometer UV-Vis showed that PS absorbs photons at a wavelength of 310 – 340 nm and PS containing POPOP produces a maximum emission at a wavelength of 421 nm. The evaluation of cesium 137 (137Cs) and cobalt 60 (60Co) gamma spectrum using the photomultiplier tube (PMT) Hamamatsu R878 showed the results of Compton spectrum characters with a gross counting maximum of 0.78 and 0.89, respectively, compared to the commercial plastic scintillator. The results of this study are expected to be usefully utilized in the development of a large-volume plastic scintillator for the radiation portal monitor (RPM).

Simulation of a Compton-pair imaging calorimeter and tracking system for the next generation of MeV gamma-ray telescopes

The astrophysical community is currently focusing its efforts in the development of a new generation of gamma-ray telescopes to detect low-energy photons in the MeV-GeV energy range, operating both in the Compton and pair conversion regimes. The reconstruction of the incident photons energy and direction is not straightforward, as the range of secondary particles produced by photon interactions is usually short. We propose a detector consisting of a tracker system based on scintillating fibers and of a Compton-pair imaging calorimeter made of CsI(Na) crystals coupled to wavelength shifting (WLS) fibers read out by Silicon Photomultiplier (SiPM) arrays. We have developed a dedicated simulation code to study the performance of this detector. The simulation takes into account the optical photon production and propagation inside the fibers and is used to optimize the fiber geometrical and optical properties and the design of the readout system.

Characterisation of Hamamatsu SiPM for cosmic muon veto detector at IICHEP

A test setup is built to characterise the SiPM and to measure muon detection efficiency of an extruded plastic scintillator detector. In the setup, light from the scintillator is readout by SiPMs using two embedded Wavelength Shifting Fibres (WLS) fibres. The SiPM was calibrated using LED source, but alternate calibration procedures using radio-active source as well as noise data were also established. The SiPM is studied at various over voltages (V ov ) and determined the operating V ov by optimising the muon detection efficiency and noise rate. The muon position along the length of the scintillator is measured using timing information from both sides of the fibres. Results from our characterisation studies of SiPM (2mm × 2mm, Model S1330-2050VE), e.g. after pulse, cross-talk, recovery time etc. will be discussed in this paper.

Characteristics of photopolymerized tissue equivalent plastic scintillator in high dose rate radiotherapy”

Recently, as the biological effects of ultrahigh-dose-rate radiation therapy (flash RT) have been verified, many kinds of research on the clinical application of high-dose-rate radiation therapy have been performed. Moreover, various studies are being performed to determine the absorbed dose in the volume of cancers. In this study, to evaluate the absorbed dose of the human body during high-dose-rate radiation therapy, a dosimeter system was developed using a tissue equivalent plastic scintillator having the same geometric structure as the Farmer-type ionization chamber, and its characteristics were evaluated. The plastic scintillator was based on PMMA, and PPO was used as the primary scintillator and POPOP as the wavelength shifter. An Irgacure 819 photo-initiator and a Hg lamp were used to polymerize of PMMA plastic scintillator. The fabricated plastic scintillator was characterized for conventional LINAC X-ray and 45 MeV proton beams. The results of this study combined with 3D printing technology are planned to be used as dosimeters for volumetric dosimetry of normal and cancerous tissues during radiation therapy.

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. The liquid argon scintillation wavelength of 127 nm is most commonly shifted to the visible range by special wavelength shifters or read out by the 127 nm sensitive photodetectors that are under development. The effective calibration and quality control of these active media 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 was designed as a small, portable and easy-to-operate device to enable the acquisition of performance characteristics of several square meters of light detectors. Here, we report on the development of the light source and its performance characteristics.

RADiCAL—Precision Timing, Ultracompact, Radiation-Hard Electromagnetic Calorimetry

To address the challenges of providing high-performance calorimetry in future hadron collider experiments under conditions of high luminosity and high radiation (FCC-hh environments), we conducted R&D on advanced calorimetry techniques suitable for such operation, based on scintillation and wavelength-shifting technologies and photosensor (SiPM and SiPM-like) technology. In particular, we focused our attention on ultra-compact radiation-hard EM calorimeters based on modular structures (RADiCAL modules) consisting of alternating layers of the very dense absorber and scintillating plates, read out via radiation hard wavelength shifting (WLS) solid fiber or capillary elements to photosensors positioned either proximately or remotely, depending upon their radiation tolerance. RADiCAL modules provide the capability to measure simultaneously and with high precision the position, energy and timing of EM showers. This paper provides an overview of the instrumentation and photosensor R&D associated with the RADiCAL program.

Generation of Single Sideband-Suppressed carrier (SSB-SC) Signal Based on Stimulated Brillouin Scattering

A novel cost-effective wavelength shifter is suggested in this paper. This paper shows how to shift signals in the mm-wave area using a frequency shifter. Due to stimulated Brillouin scattering in optical fibre, the proposed approach produces a single sideband signal without the carrier signal. When compared to SSB-SC transmissions, the bandwidth efficiency of double sideband signals is lower. Because it employs an optical fibre with a performance degrading condition such as SBS as an application, the frequency shifter is entirely optical. The theory of Gain and Loss Spectrum of SBS within optical fibre is utilised to minimise the upshifted frequency component and boost the low shifter frequency component in order to generate improved carrier power and single sideband. The SBS phenomenon produces a single sideband, which is advantageous in advanced modulation systems and consumes less bandwidth. It’s worth noting that the SSB-SC signal may be generated using any optical approach, and the proposed work eliminates the need for non-optical components like 90-degree hybrid couplers. SSB-SC signals are capable of combating pulse broadening difficulties and have the ability to operate at terahertz frequencies. Transmission of an SSB-SC signal is also shown to validate the performance of the produced signal. Furthermore, the Q factor of SSB-SC, SSB with carrier, DSB-SC, and DSB with carrier signals is studied at various connection lengths.

Ultraviolet-induced fluorescence of poly(methyl methacrylate) compared to 1,1,4,4-tetraphenyl-1,3-butadiene down to 4 K

Several particle-physics experiments use poly(methyl methacrylate) (a.k.a. PMMA or acrylic) vessels to contain liquid scintillators. Superluminal charged particles emitted from radioactive impurities in or near the acrylic can emit Cherenkov radiation in the ultraviolet (UV) spectra range. If acrylic fluoresces in the visible range due to this UV light, it could be a source of background in experiments where the main signal is visible scintillation light, or UV scintillation light that is absorbed and re-emitted at visible wavelengths by a wavelength shifter. Some of these experiments operate at low temperature. The fluorescence of these materials could change with temperature so we have studied the fluorescence of the acrylic used in the DEAP-3600 experiment down to a temperature of 4 K, and compared it to the common wavelength shifter 1,1,4,4-tetraphenyl-1,3-butadiene (TPB). The light yield and wavelength spectra of these materials were characterized by exciting the sample with 285 nm UV light, which acted as a proxy for Cherenkov light in the detector. Spectral measurements indicate at least part of the fluorescence of the acrylic is due to additives. Time-resolved measurements show the light yields of our acrylic sample, TPB sample, and the relative light between both samples, all increase when cooling down. At room temperature, the light yield of our acrylic sample relative to the TPB sample is 0.27%, while it reaches 0.48% at 4 K. The main fluorescence time constant of the acrylic is less than a few nanoseconds.

Qualification study of SiPMs on a large scale for the CMVD Experiment

A Cosmic Muon Veto (CMV) detector using extruded plastic scintillators is being designed around the mini-Iron Calorimeter (mini-ICAL) detector at the transit campus of the India based Neutrino Observatory, Madurai for the feasibility study of shallow depth underground experiments. The scintillation signals that are produced in the plastic due to muon trajectories are absorbed by wavelength shifting (WLS) fibres. The WLS fibres re-emit photons of longer wavelengths and propagate those to silicon photo-multipliers (SiPMs). The SiPMs detect these photons, producing electronic signals. The CMV detector will use more than 700 scintillators to cover the mini-ICAL detector and will require around 3000 SiPMs. The design goal for the cosmic muon veto efficiency of the CMV is >99.99%. Hence, every SiPM used in the detector needs to be tested and characterised to satisfy the design goal of CMV. A mass testing system was developed for the measurement of gain and choice of the overvoltage (V ov) of each SiPMs using an LED driver. The V ov is obtained by studying the noise rate, the gain of the SiPM. This paper describes the experimental setup used to test the SiPMs characteristics along with detailed studies of those characteristics as a function of temperature.

R &D of wavelength-shifting reflectors and characterization of the quantum efficiency of tetraphenyl butadiene and polyethylene naphthalate in liquid argon

Detectors based on liquid argon (LAr) often require surfaces that can shift vacuum ultraviolet (VUV) light and reflect the visible shifted light. For the LAr instrumentation of the LEGEND-200 neutrinoless double beta decay experiment, several square meters of wavelength-shifting reflectors (WLSR) were prepared: the reflector Tetratex® (TTX) was in-situ evaporated with the wavelength shifter tetraphenyl butadiene (TPB). For even larger detectors, TPB evaporation will be more challenging and plastic films of polyethylene naphthalate (PEN) are considered as an option to ease scalability. In this work, we first characterized the absorption (and reflectivity) of PEN, TPB (and TTX) films in response to visible light. We then measured TPB and PEN coupled to TTX in a LAr setup equipped with a VUV sensitive photomultiplier tube. The effective VUV photon yield in the setup was first measured using an absorbing reference sample, and the VUV reflectivity of TTX quantified. The characterization and simulation of the setup along with the measurements and modelling of the optical parameters of TPB, PEN and TTX allowed to estimate the absolute quantum efficiency (QE) of TPB and PEN in LAr (at 87K) for the first time: these were found to be above 67 and 49%, respectively (at 90% CL). These results provide relevant input for the optical simulations of experiments that use TPB in LAr, such as LEGEND-200, and for experiments that plan to use TPB or PEN to shift VUV scintillation light.

The Effect of Wavelength Shifting Fibers on Cherenkov Glass Detectors for Gamma-Ray Measurements

Cherenkov detectors have been developed and used in several fields since the discovery of Cherenkov radiation. They do have several advantages compared with other detector types, such as low noise due to the low-energy threshold of Cherenkov radiation and short decay constant (on the order of picoseconds). However, the light yield of Cherenkov detectors is low. Only several hundreds of Cherenkov photons can be generated per megaelectron-volt. The objective of this work is to manufacture and test Cherenkov glass detectors for detection of high-energy gammas. The focus is to improve the light output of Cherenkov detectors by implementing wavelength shifting (WLS) fibers inside the glass samples. 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 the photon wavelength and photon detector quantum efficiency.

Progress in Fast and Red Plastic Scintillators

Radiological detection where Cherenkov residual background can be prominent requires scintillators with increased emission wavelength. Cherenkov residual background precludes the use of UV-emitting sensors such as plastic scintillators. However, the literature is scarce in red-emitting plastic scintillators and only one commercial scintillator is currently available (BC-430, from Saint-Gobain Crystals and Detectors). In addition, X-ray imaging or time-of-flight positron emission tomography (ToF-PET) applications are also demanding on this type (color) of scintillators, but such applications also require that the material displays a fast response, which is not particularly the case for BC-430. We present herein our latest developments in the preparation and characterization of fast and red plastic scintillators for this application. Here, ‘fast’ means nanosecond range decay time and ‘red’ is an emission wavelength shifted towards more than 550 nm. At first, the strategy to the preparation of such material is explained by decomposing the scintillator to fundamental elements. Each stage is then optimized in terms of decay time response, then the elemental bricks are arranged to give plastic scintillator formulations that are compatible with the abovementioned characteristics. The results are compared with the red-emissive BC-430 commercial plastic, and the ultra-fast, violet-emitting BC-422Q 1% plastic. In particular, the first-time use of trans-4-dimethylamino-4′-nitrostilbene in the scintillation field as a red wavelength shifter allowed preparing plastic scintillators with the following properties: λemmax 554 nm, photoluminescence decay time 4.2 ns, and light output ≈ 6100 ph/MeV. This means a scintillator almost as bright as BC-430 but at least three times faster. This new sensor might provide useful properties for nuclear instrumentation.

Scintillation light detection in the 6-m drift-length ProtoDUNE Dual Phase liquid argon TPC

DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE Dual Phase (DP) is a 6 times 6 times 6 m^3 liquid argon time-projection-chamber (LArTPC) that recorded cosmic-muon data at the CERN Neutrino Platform in 2019–2020 as a prototype of the DUNE Far Detector. Charged particles propagating through the LArTPC produce ionization and scintillation light. The scintillation light signal in these detectors can provide the trigger for non-beam events. In addition, it adds precise timing capabilities and improves the calorimetry measurements. In ProtoDUNE-DP, scintillation and electroluminescence light produced by cosmic muons in the LArTPC is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. In this paper, the ProtoDUNE-DP photon detection system performance is evaluated with a particular focus on the different wavelength shifters, such as PEN and TPB, and the use of Xe-doped LAr, considering its future use in giant LArTPCs. The scintillation light production and propagation processes are analyzed and a comparison of simulation to data is performed, improving understanding of the liquid argon properties.

Simulation study on photon generation and collection of tower applied to NICA-MPD electromagnetic calorimeter

Shashlik tower, which is composed of absorbers and scintillators alternately, surrounded by reflector and coupled with Silicon Photomultiplier (SiPM) by Wavelength-Shifting (WLS) fibers, is a significant component to measure the energy and position of photons and electrons in Electromagnetic Calorimeter (ECal), a key detector of the Multi Purpose Detector (MPD) at the Nuclotron-based Ion Collider facility (NICA) in Russia. In this paper, the effect of materials adopted for absorber, reflector and WLS fiber, the length and curvature of fibers and the electrons incident position on photons transmission performance of tower is simulated based on GEANT4 software. The impact of Gaussian deviation's electron beam energy and spread of 10% in the energy range on the energy resolution of tower is also studied. Results show that the low polishing degree absorber, the high polishing degree TiO_2 reflector and the type of Y-11 WLS fibers bent with a curvature radius of greater than 11 cm can significantly improve the light output. In addition, electrons injected along the centre of tower can make photons position distribution in SiPM more uniform. The generation time of photons in scintillators and time of arrival at the SiPM both obey the Landau distribution. Finally, the energy resolution of tower can be better than 3.8%/√(E) (GeV) for a Gaussian deviation's electron beam with an average energy of 3 GeV and spread of 10% in the energy range.

Direct comparison of PEN and TPB wavelength shifters in a liquid argon detector

A large number of particle detectors employ liquid argon as their target material owing to its high scintillation yield and its ability to drift ionization charge over large distances. Scintillation light from argon is peaked at 128 nm and a wavelength shifter is required for its efficient detection. In this work, we directly compare the light yield achieved in two identical liquid argon chambers, one of which is equipped with polyethylene naphthalate (PEN) and the other with tetraphenyl butadiene (TPB) wavelength shifter. Both chambers are lined with enhanced specular reflectors and instrumented with SiPMs with a coverage fraction of approximately 1%, which represents a geometry comparable to the future large scale detectors. We measured the light yield of the PEN chamber to be 39.4,pm ,0.4(stat),pm ,1.9(syst)% of the yield of the TPB chamber. Using a Monte Carlo simulation this result is used to extract the wavelength shifting efficiency of PEN relative to TPB equal to 47.2,pm ,5.7%. This result paves the way for the use of easily available PEN foils as a wavelength shifter, which can substantially simplify the construction of future liquid argon detectors.

Fluorescence of pyrene-doped polystyrene films from room temperature down to 4 K for wavelength-shifting applications

In liquid argon-based particle detectors, slow wavelength shifters (WLSs) could be used alongside the common, nanosecond scale, WLS tetraphenyl butadiene (TPB) for background mitigation purposes. At room temperature, pyrene has a moderate fluorescence light yield (LY) and a time constant of the order of hundreds of nanoseconds. In this work, four pyrene-doped polystyrene films with various purities and concentrations were characterized in terms of LY and decay time constants in a range of temperature between 4 K and 300 K under ultraviolet excitation. These films were found to have a LY between 35 and 50% of that of evaporated TPB. All light yields increase when cooling down, while the decays slow down. At room temperature, we observed that pyrene purity is strongly correlated with emission lifetime: highest obtainable purity samples were dominated by decays with emission time constants of ∼ 250–280 ns, and lower purity samples were dominated by an ∼ 80 ns component. One sample was investigated further to better understand the monomer and excimer emissions of pyrene. The excimer-over-monomer intensity ratio decreases when the temperature goes down, with the monomer emission dominating below ∼ 87 K.

Characterization of the scintillation time response of liquid argon detectors for dark matter search

The scintillation time response of liquid argon has a key role in the discrimination of electronic backgrounds in dark matter search experiments. However, its extraordinary rejection power can be affected by various detector effects such as the delayed light emission of TetraPhenyl Butadiene, the most commonly used wavelength shifter, and the electric drift field applied in Time Projection Chambers. In this work, we characterized the TetraPhenyl Butadiene delayed response and the dependence of the pulse shape discrimination on the electric field, exploiting the data acquired with the ARIS, a small-scale single-phase liquid argon detector exposed to monochromatic neutron and gamma sources at the ALTO facility of IJC Lab in Orsay.

Characterization of Silicon-Photomultipliers for a Cosmic Muon Veto detector

A Cosmic Muon Veto (CMV) detector using extruded scintillators is being designed around the mini-Iron Calorimeter detector at the transit campus of the India-based Neutrino Observatory, Madurai for measuring its efficiency at shallow depth underground experiments. The scintillation signal is transmitted through a Wavelength Shifting (WLS) fibre and readout by Hamamatsu Silicon-Photomultipliers (SiPMs). A Light Emitting Diode (LED) system is included on the front-end readout for in-situ calibration of the gain of each SiPM. A characterization system was developed for the measurement of gain and choice of the overvoltage (V ov) of SiPMs using the LED as well as a cosmic muon telescope. The V ov is obtained by studying the noise rate, the gain of the SiPM, and the muon detection efficiency. In case of any malfunction of the LED system during the operation, the SiPM can also be calibrated with the noise data as well as using radioactive sources. This paper describes the basic characteristics of the SiPM and the comparison of the calibration results using all three methods, as well as the V ov of the SiPMs and muon selection criteria for the veto detector.