UV-glass photomultiplier tubes (PMTs) have poor photon detection efficiency for wavelengths below $300\,\text{nm}$ due to the opaqueness of the window material. Costly quartz PMTs could be used to enhance the efficiency below $300\,\text{nm}$. A less expensive solution that dramatically improves this efficiency is the application of a thin film of a p-terphenyl (PT) wavelength shifter on UV-glass PMTs. This improvement was quantified for Photonis XP4500B PMTs for wavelengths between $200\,\text{nm}$ and $400\,\text{nm}$. The gain factor ranges up to 5.4 $\pm$ 0.5 at a wavelength of $215\,\text{nm}$, with a material load of $110\pm10\,μ\text{g}/\text{cm}^2$ ($894\,\text{nm}$). The wavelength shifter was found to be fully transparent for wavelengths greater than $300\,\text{nm}$. The resulting gain in detection efficiency, when used in a typical Cherenkov counter, was estimated to be of the order of 40\%. Consistent coating quality was assured by a rapid gain testing procedure using narrow-band UV LEDs. Based on these results, 200 Photonis XP4500B PMTs were treated with PT for the upgraded low-threshold Cherenkov counter (LTCC) to be used in the CEBAF Large Acceptance Spectrometer upgraded detector (CLAS12) at the Thomas Jefferson National Accelerator Facility.
A SensL MicroFC-SMT-60035 6x6 mm$^2$ silicon photo-multiplier coated with a NOL-1 wavelength shifter have been tested in the liquid xenon to detect the 175-nm scintillation light. For comparison, a Hamamatsu vacuum ultraviolet sensitive MPPC VUV3 3x3 mm$^2$ was tested under the same conditions. The photodetection efficiency of $13.1 \pm 2.5$% and $6.0 \pm 1.0$%, correspondingly, is obtained.
The light yield of a water-based Cherenkov detector can be significantly improved by adding a wavelength shifter. Wavelength shifter (WLS) molecules absorb ultraviolet photons and re-emit them at longer wavelengths where typical photomultiplier tubes are more sensitive. In this study, several wavelength shifter compounds are tested for possible deployment in the Sudbury Neutrino Observatory (SNO). Test results on optical properties and chemical compatibility for a few WLS candidates are reported; together with timing and gain measurements. A Monte Carlo simulation of the SNO detector response …
Wavelength shifters and their applications for liquid argon detectors have been a subject of extensive R&D over the past decade. This work reviews the most recent results in this field. We compare the optical properties and usage details together with the associated challenges for various wavelength shifting solutions. We discuss the current status and potential future R&D directions for the main classes of wavelength shifters.
We have evaluated the performance of a Ce-doped fused-silica fiber as wavelength shifter coupled to a CeF$_{3}$ crystal using electron beams at CERN. The pulse shape and collection efficiency were measured using irradiated (100 kGy) and un-irradiated fibers. In addition, we evaluated the light yield of various Ce-doped fibers and explored the possibility of using them in the future, including for precision timing applications in a high-luminosity collider environment.
DEAP-3600 uses liquid argon contained in a spherical acrylic vessel as a target medium to perform a sensitive spin-independent dark matter search. Argon scintillates in the vacuum ultraviolet spectrum, which requires wavelength shifting to convert the VUV photons to visible so they can be transmitted through the acrylic light guides and detected by the surrounding photomultiplier tubes. The wavelength shifter 1,1,4,4-tetraphenyl-1,3-butadiene was evaporatively deposited to the inner surface of the acrylic vessel under vacuum. Two evaporations were performed on the DEAP-3600 acrylic vessel with…
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 nanostructu…
A novel concept for detection and spectroscopy of gamma rays, and detection of thermal neutrons based on codoped lanthanum fluoride nanocrystals containing gadolinium is presented.The trends of colloidal synthesis of the mentioned material, LaF3 co-doped with Ce as the activator, Yb as the wavelength-shifter and Gd as the neutron captor, is reported. Nanocrystals of the mentioned material were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), optical absorption, and photoluminescence spectroscopy. Gamma detection and i…
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 instrumen…
For the first time a molecule of 2-(4-styrylphenyl)benzoxazole containing benzoxazole and stilbene groups is applied as a scintillator dopant acting as a wavelength shifter. In this article a light yield of the plastic scintillator, prepared from styrene doped with 2 wt% of 2,5-diphenylbenzoxazole and 0.03 wt% of 2-(4-styrylphenyl)benzoxazole, is determined to be as large as 60% $\pm$ 2% of the anthracene light output. There is a potential to improve this value in the future by the optimization of the additives concentrations.
Liquid noble based particle detectors often use the organic wavelength shifter 1,1,4,4- tetraphenyl-1,3-butadiene (TPB) which shifts UV scintillation light to the visible regime, facilitating its detection, but which also can scintillate on its own. Dark matter searches based on this type of detector commonly rely on pulse-shape discrimination (PSD) for background mitigation. Alpha-induced scintillation therefore represents a possible background source in dark matter searches. The timing characteristics of this scintillation determine whether this background can be mitigated through PSD. We ha…
To optimise the design of the light readout in the ArDM 1-ton liquid argon dark matter detector, a range of reflector and WLS coating combinations were investigated in several small setups, where argon scintillation light was generated by radioactive sources in gas at normal temperature and pressure and shifted into the blue region by tetraphenyl butadiene (TPB). Various thicknesses of TPB were deposited by spraying and vacuum evaporation onto specular 3M{\small\texttrademark}-foil and diffuse Tetratex{\small\textregistered} (TTX) substrates. Light yields of each reflector and TPB coating comb…
A novel plastic scintillator, referred to as J-PET scintillator, has been developed for the application in the digital positron emission tomography (PET). The novelty of the concept lies in application of the 2-(4-styrylphenyl)benzoxazole as a wavelength shifter. To date, the chemical compound has not been used as scintillator additive. A role of wavelength shifter is to shift the scintillation spectrum towards longer wavelengths making it more suitable for applications in scintillators of long strips geometry because of larger attenuation length, and light detection with digital silicon photo…
Liquid argon-based scintillation detectors are important for dark matter searches and neutrino physics. Argon scintillation light is in the vacuum ultraviolet region, making it hard to be detected by conventional means. Polyethylene naphthalate (PEN), an optically transparent thermoplastic polyester commercially available as large area sheets or rolls, is proposed as an alternative wavelength shifter to the commonly-used tetraphenyl butadiene (TPB). By combining the existing literature data and spectrometer measurements relative to TPB, we conclude that the fluorescence yield and timing of bot…
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 …
The alpha induced scintillation of the wavelength shifter 1,1,4,4-tetraphenyl-1,3-butadiene (TPB) was studied to improve the understanding of possible surface alpha backgrounds in the DEAP dark matter search experiment. We found that vacuum deposited thin TPB films emit 882 +/-210 photons per MeV under alpha particle excitation. The scintillation pulse shape consists of a double exponential decay with lifetimes of 11 +/-5 ns and 275 +/-10ns.
Liquid argon is commonly used as a detector medium for neutrino physics and dark matter experiments in part due to its copious scintillation light production in response to its excitation and ionization by charged particle interactions. As argon scintillation appears in the vacuum ultraviolet (VUV) regime and is difficult to detect, wavelength-shifting materials are typically used to convert VUV light to visible wavelengths more easily detectable by conventional means. In this work, we examine the wavelength-shifting and optical properties of poly(ethylene naphthalate) (PEN), a recently propos…
The ARAPUCA concept has been proposed as a simple and neat solution for increasing the effective collection area of SiPMs through the shifting and trapping of scintillation light in noble liquids, thus with great potential for improving timing and calorimetry resolution in neutrino and dark matter search experiments using time projection chambers. It is expected to achieve a single photon detection efficiency larger than 1\%. The initial design consists of a box made of highly reflective internal surface material and with an acceptance window for photons composed of two shifters and a dichroic…
The scintillation detection systems of liquid argon time projection chambers (LArTPCs) require wavelength shifters to detect the 128 nm scintillation light produced in liquid argon. Tetraphenyl butadiene (TPB) is a fluorescent material that can shift this light to a wavelength of 425 nm, lending itself well to use in these detectors. We can coat the glass of photomultiplier tubes (PMTs) with TPB or place TPB-coated plates in front of the PMTs. In this paper, we investigate the degradation of a chemical TPB coating in a laboratory or factory environment to assess the viability of long-term TPB …
Scintillation light from liquid noble gas in a neutrino or dark matter experiment lies typically within the vacuum ultraviolet (VUV) region and might be strongly absorbed by surrounding materials such as light guides or photomultiplier. Tetraphenyl butadiene (TPB) is a fluorescent material and acts as a wavelength shifter (WLS) which can turn the UV light to the visible light around a peak wavelength of 425 nm, enabling the light signals to be detected easily for physics study. Compared with a traditional TPB coating method using vapor deposition, we propose an alternative technique with a spi…
The scintillation light of liquid argon has been recorded wavelength and time resolved with very good statistics in a wavelength interval ranging from 118 nm through 970 nm. Three different ion beams, protons, sulfur ions and gold ions, were used to excite liquid argon. Only minor differences were observed in the wavelength-spectra obtained with the different incident particles. Light emission in the wavelength range of the third excimer continuum was found to be strongly suppressed in the liquid phase. In time-resolved measurements, the time structure of the scintillation light can be directl…
ArDM is a new-generation WIMP detector which will measure simultaneously light and charge from scintillation and ionization of liquid argon. Our goal is to construct, characterize and operate a 1 ton liquid argon underground detector. The project relies on the possibility to extract the electrons produced by ionization from the liquid into the gas phase of the detector, to amplify and read out with Large Electron Multipliers detectors. Argon VUV scintillation light has to be converted with wavelength shifters such as TetraPhenyl Butadiene in order to be detected by photomultipliers with bialka…
Cherenkov detectors employ various methods to maximize light collection at the photomultiplier tubes (PMTs). These generally involve the use of highly reflective materials lining the interior of the detector, reflective materials around the PMTs, or wavelength-shifting sheets around the PMTs. Recently, the use of water-soluble wavelength-shifters has been explored to increase the measurable light yield of Cherenkov radiation in water. These wave-shifting chemicals are capable of absorbing light in the ultravoilet and re-emitting the light in a range detectable by PMTs. Using a 250 L water Cher…
The use of efficient wavelength-shifters from the vacuum-ultraviolet to the photosensor's range of sensitivity is a key feature in detectors for Dark Matter search and neutrino physics based on liquid argon scintillation detection. Thin film of Tetraphenyl-butadiene (TPB) deposited onto the surface delimiting the active volume of the detector and/or onto the photosensor optical window is the most common solution in current and planned experiments. Detector design and response can be evaluated and correctly simulated only when the properties of the optical system in use (TPB film + substrate) a…
Tetraphenyl-butadiene (TPB) is an organic fluorescent chemical compound generally used as wavelength shifter thanks to its extremely high efficiency to convert ultra-violet photons into visible light. A common method to use TPB with detectors sensitive to visible light, such as photomultiplier tubes (PMTs), is to deposit thin layers on the device window. To obtain effective TPB layers, different procedures can be used. In this work a specific evaporation technique adopted to coat 8 in. convex windows photomultiplier tubes is presented. It consists in evaporating TPB by means of a Knudsen cell,…
TetraPhenyl Butadiene is the wavelength shifter most widely used in combination with liquid Argon. The latter emits scintillation photons with a wavelength of 127 nm that need to be downshifted to be detected by photomultipliers with glass or quartz windows. TetraPhenyl Butadiene has been demonstrated to have an extremely high conversion efficiency, possibly higher than 100 % for 127 nm photons, while there is no precise information about the time dependence of its emission. It is usually assumed to be exponentially decaying with a characteristic time of the order of one ns, as an extrapolatio…
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 w…
Hyper-Kamiokande, the next generation large water Cherenkov detector in Japan, is planning to use approximately 80,000 20-inch photomultiplier tubes (PMTs). They are one of the major cost factors of the experiment. We propose a novel enhanced photon trap design based on a smaller and more economical PMT in combination with wavelength shifters, dichroic mirrors, and broadband mirrors. GEANT4 is utilized to obtain photon collection efficiencies and timing resolution of the photon traps. We compare the performance of different trap configurations and sizes. Our simulations indicate an enhanced ph…
The Liquid Argon Time Projection Chambers (LArTPCs) are a choice for the next generation of large neutrino detectors due to their optimal performance in particle tracking and calorimetry. The detection of Argon scintillation light plays a crucial role in the event reconstruction as well as the time reference for non-beam physics such as supernovae neutrino detection and baryon number violation studies. In this contribution, we present the current R&D work on the ARAPUCA (Argon R&D Advanced Program at UNICAMP), a light trap device to enhance Ar scintillation light collection and thus the overal…
This paper reports the results of an experiment to directly measure the time-resolved scintillation signal from the passage of cosmic-ray muons through liquid argon. Scintillation light from these muons is of value to studies of weakly-interacting particles in neutrino experiments and dark matter searches. The experiment was carried out at the TallBo dewar facility at Fermilab using prototype light guide detectors and electronics developed for the Deep Underground Neutrino Experiment. Two models are presented for the time structure of the scintillation light, a phenomenological model and a com…
Measurement of the X-ARAPUCA's Absolute Photon Detection Efficiency for the Deep Underground Neutrino Experiment's Vertical Drift Far Detector
Istituto Nazionale di Fisica Nucleare, Sezione di Napoli（意大利国家核物理研究所那不勒斯分部）；University of Padova（帕多瓦大学）；University of Milano Bicocca（米兰比可卡大学）；Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT)（能源、环境与技术研究中心）
Production and installation of wavelength-shifting reflective light enhancers for the Short-Baseline Near Detector
Argonne National Laboratory（阿贡国家实验室）；Brookhaven National Laboratory（布鲁克海文国家实验室）；University of California, Santa Barbara（加州大学圣塔芭芭拉分校）；Center for Information Technology Renato Archer（雷纳托·阿切尔信息技术中心）；University of Chicago（芝加哥大学）；Colorado State University（科罗拉多州立大学）；Columbia University（哥伦比亚大学）；University of Edinburgh（爱丁堡大学）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；University of Florida（佛罗里达大学）；Illinois Institute of Technology（伊利诺伊理工学院）；Imperial College London（伦敦帝国理工学院）；University of Kansas（堪萨斯大学）；Lancaster University（兰卡斯特大学）；University of Liverpool（利物浦大学）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Louisiana State University（路易斯安那州立大学）；University of Manchester（曼彻斯特大学）；University of Michigan（密歇根大学）；University of Minnesota（明尼苏达大学）；Mount Holyoke College（蒙特霍利约克学院）；University of Notre Dame（圣母大学）；University of Oxford（牛津大学）；University of Pennsylvania（宾夕法尼亚大学）；Queen Mary University of London（伦敦大学玛丽女王学院）；Rutgers University（罗格斯大学）；University of Sheffield（谢菲尔德大学）；University of Sussex（萨塞克斯大学）；Syracuse University（雪城大学）；University of Texas at Arlington（德克萨斯大学阿灵顿分校）；Tufts University（塔夫茨大学）；Center for Neutrino Physics, Virginia Tech（弗吉尼亚理工大学中微子物理中心）；University of Warwick（华威大学）
DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE Dual Phase (DP) is a 6x6x6m3 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 measu…
