WLS Fibers Research Articles

New experiment at J-PARC to measure the muon neutrino cross section ratio between water and hydrocarbon

A new experiment, named WAGASCI can precisely measure the ratio of muon neutrino cross sections between water and hydrocarbon for charged-current interactions with a large angular acceptance at J-PARC. A new detector mainly consists of two water target modules and two hydrocarbon target modules. Each module is composed of scintillators aligned in a 3D grid-like structure having almost 4π solid angle acceptance. Each scintillator has a groove for a WLS fiber to be put on, and they are glued with the optical cement by using a semi-automated gluing system. WLS fibers are connected to Multi-Pixel Photon Counters (MPPCs), which are crosstalk suppression type. The detector is now under construction, and we will start taking the data in 2017.

K-long and muon system for the Belle II experiment

We have studied a system based on scintillator counters with WLS fiber light collection and SiPM readout for the Belle II experiment. We have identified a few simple improvements in the strip production technology which allow significant increases in the light collection efficiency, thus increasing the efficiency and robustness of the entire detector. The new system should work efficiently at background rates and radiation doses ∼100 times larger than those observed for the Belle experiment. As demonstrated by many tests, the system has sufficient robustness to operate well in a strong magnetic field and high radiation and interaction environment with no significant degradation anticipated after many years of data taking. While this system was designed for a particular experiment, namely Belle II, our study can be applied to the construction of muon systems in many experiments.

Multisector scintillation detector with fiber-optic light collection

A new type of scintillation detector for the use in high energy physics is described. The octagonal detector consists of eight triangular scintillator sectors with total area of 1 m2. Each sector represents two plates of 2 cm thick plastic scintillator. Seven 1 mm thick WLS fibers are laid evenly between the plates. The space between the fibers is filled with silicone compound to provide better light collection. Fiber ends from all eight sectors are gathered in the central part of the detector into a bunch and docked to the cathode of a FEU-115m photomultiplier. The read-out of the counter signals is carried out from 7th and 12th dynodes, providing a wide dynamic range up to about 10000 particles. The front-end electronics of the detector is based on the flash-ADC with a sampling frequency of 200 MHz. The features of detecting and recording systems of the multisector scintillation detector (MSD) and the results of its testing are discussed.

Development of scintillator detector for detection of cosmic ray shower

An array of plastic scintillator detectors is proposed for detection of cosmic ray showers at an altitude of about 2200 meters above sea level in the Himalayas at the Centre for Astroparticle Physics & Space Sciences, Darjeeling campus of Bose Institute. Each element of this array is a 1 m × 1 m plastic scintillator detector of thickness 2 cm, coupled with WLS fibers and a PMT. During the first phase seven of these modules arranged in an hexagonal way keeping one at the centre of the hexagon will be commissioned. Four such modules have already been built and tested. As a proof of principle three of these detectors are used to detect cosmic ray shower. The preliminary results are presented.

Increase in the light collection from a scintillation strip with a hole for the WLS fiber using filling materials of various types

The light collection of extruded scintillation strip samples with the help of WLS fibers placed in a longitudinal hole inside of the plates has been measured. The holes are filled with various liquid fillers. Measurements are performed under irradiation by cosmic muons. A method for pumping a liquid filler with a viscosity of more than 10 Pa s into the strip hole with a WLS fiber inside is devised and successfully tested.

Test beam studies of the light yield, time and coordinate resolutions of scintillator strips with WLS fibers and SiPM readout

Prototype scintilator+WLS strips with SiPM readout for large muon detection systems were tested in the muon beam of the Fermilab Test Beam Facility. Light yield of up to 137photoelectrons per muon per strip has been observed , as well as time resolution of 330ps and position resolution along the strip of 5.4cm.

A 16-ch module for thermal neutron detection using ZnS:6LiF scintillator with embedded WLS fibers coupled to SiPMs and its dedicated readout electronics

A scalable 16-ch thermal neutron detection system has been developed in the framework of the upgrade of a neutron diffractometer. The detector is based on a ZnS:6LiF scintillator with embedded WLS fibers which are read out with SiPMs. In this paper, we present the 16-ch module, the dedicated readout electronics, a direct comparison between the performance of the diffractometer obtained with the current 3He detector and with the 16-ch detection module, and the channel-to-channel uniformity.

Digital signal processing for a thermal neutron detector using ZnS(Ag):6LiF scintillating layers read out with WLS fibers and SiPMs

We present a digital signal processing system based on a photon counting approach which we developed for a thermal neutron detector consisting of ZnS(Ag):6LiF scintillating layers read out with WLS fibers and SiPMs. Three digital filters have been evaluated: a moving sum, a moving sum after differentiation and a digital CR-RC4 filter. The performances of the detector with these filters are presented. A full analog signal processing using a CR-RC4 filter has been emulated digitally. The detector performance obtained with this analog approach is compared with the one obtained with the best performing digital approach.

Detection of thermal neutrons using ZnS(Ag):6LiF neutron scintillator read out with WLS fibers and SiPMs

In this paper we present the development of a one-dimensional multi-channel thermal neutron detection system for the application in neutron scattering instrumentation, e.g. strain-scanning diffractometers. The detection system is based on ZnS(Ag):6LiF neutron scintillator with embedded WLS fibers which are read out with a SiPM. A dedicated signal processing system allows us to suppress the SiPM dark counts and to extract the signals from the neutron absorption events.For a single-channel detection unit which represents the elementary building block of this detection system we achieved a neutron detection efficiency of ~65% at 1.2Å, a background count rate <10−3Hz and a gamma-sensitivity <10−6 (measured with a 60Co source), while the dead time is ~20μs and the multi-count ratio is <1%. This performance was achieved even for SiPM dark count rates of up to ~2MHz.

A new-concept calorimeter for future neutrino beams based on Kaon tagging

Neutrino cross-section measurements are an essential requirement for the next generation of neutrino oscillation experiments and they are presently limited by uncertainties on neutrino fluxes. In [1] we propose to instrument a neutrino decay tunnel to detect large angle positrons and tag the three-body semileptonic K+→e+π0νe decays. In such a facility the absolute electron neutrino flux could be determined with unprecedented precision (O(1%)). An e+/π+ separation capability of about 2% as well as a high e+ efficiency is required for a diffuse particle source over a length of several tens of meters. Additional constraints, due to the harsh beam environment, involve radiation hardness and fast response. For this purpose we propose a specialized shashlik calorimeter (copper-scintillator) with a compact readout based on small-area Silicon PhotoMultipliers coupled to WLS fibers. The setup would allow an effective longitudinal segmentation for electron/hadron separation, reducing the dead zones introduced by fiber bundling. Detailed Monte Carlo simulations are in progress. The construction of a small prototype and exposures to pion and electron beams are foreseen.

Muon detector of the Tunka-HiSCORE project

The use of muon detectors in order to improve the rejection of background EAS produced by protons and nuclei is proposed as part of the wide-aperture Tunka-HiSCORE γ-ray telescope project. The area of the muon detector and the depth of the bulk soil layer required for effective suppression of the electron-photon component of EAS are substantiated. Results from tests of the IHEP muon detector with light collected by WLS fibers are discussed.

A SiPM-based ZnS:6LiF scintillation neutron detector

In the work presented here we built and evaluated a single-channel neutron detection unit consisting of a ZnS:6LiF scintillator with embedded WLS fibers readout by a SiPM. The unit has a sensitive volume of 2.4×2.8×50mm3; 12 WLS fibers of diameter 0.25mm are uniformly distributed over this volume and are coupled to a 1×1mm2 active area SiPM. We report the following performance parameters: neutron detection efficiency ~65% at 1.2Å, background count rate <10−3Hz, gamma-sensitivity with 60Co source <10−6, dead time ~20μs, multi-count ratio <1%. All these parameters were achieved up to the SiPM dark count rate of ~2MHz.We consider such detection unit as an elementary building block for realization of one-dimensional multichannel detectors for applications in the neutron scattering experimental technique. The dimensions of the unit and the number of embedded fibers can be varied to meet the specific application requirements. The upper limit of ~2MHz on the SiPM dark count rate allows to use SiPMs with larger active areas if required.

Strip detectors for a portal monitor application

A design for a new equipment for non intrusive inspection of containers in ports is described. The project involves the construction of a ∼ 125 m3 cosmic muon-tracking detector, to measure the deflection of cosmic muons when traversing high-Z materials. The apparatus consists of four X-Y charged particle detector planes, two placed below and two above the container to be inspected. The detection planes are segmented into 300 cm long, 1 cm2 square plastic scintillating strips with embedded WLS fibers that transport the scintillation light to photo-sensors (SiPMs) at one end of the fiber. Detailed GEANT4 simulations have demonstrated the possibility of reconstructing a 3D image of the container volume in a reasonable amount of time, compatible with the requirements of a fast inspection technique.

Time resolution measurements of scintillating counters for a new NA62 trigger charged hodoscope

The results of time resolution measurements on cosmic muons with MWPC chambers as a tracking system are presented. Two options of dual SiPM readout considered: direct light collection from opposite cut corners of the scintillator and light collection using two oppositely directed bundles of WLS fibers. Two types of SiPMs are used: S10985-050C and MicroFB-60035. The best result achived using mean-time between two SiPMs. For the direct readout from 134 × 107 × 20 mm3 scintillator time resolution σ = 300±10 ps and maximum signal arrival time spread ΔT = 1.6±0.2 ns. Using WLS fiber readout option with 265 × 107 × 30 mm3 scintillator tile signal arrival time spread ΔT = 150±50 ps and time resolution σ = 370±10 ps.

Evaluation of two thermal neutron detection units consisting of ZnS/6LiF scintillating layers with embedded WLS fibers read out with a SiPM

Two single channel detection units for thermal neutron detection are investigated in a neutron beam. They consist of two ZnS/6LiF scintillating layers sandwiching an array of WLS fibers. The pattern of these units can be repeated laterally and vertically in order to build up a one-dimensional position sensitive multi-channel detector with the needed sensitive surface and with the required neutron absorption probability. The originality of this work arises from the fact that the WLS fibers are read out with SiPMs instead of the traditionally used PMTs or MaPMTs. The signal processing system is based on a photon counting approach. For SiPMs with a dark count rate as high as 0.7MHz, a trigger efficiency of 80% is achieved together with a system background rate lower than 10−3Hz and a dead time of 30μs. No change of performance is observed for neutron count rates of up to 3.6kHz.

Large plastic scintillator panels with WLS fiber readout: Optimization of components

Results are presented on R&D efforts to design and build large size veto panels, optimized for underground low background experiments, in the most efficient and economical way using commercially available components. A variety of plastic scintillators, photomultiplier tubes, wavelength shifting fibers, and light reflector combinations were tested. Results of these studies and performance of a 2.2m long panel are presented.

Improvement of radiation hardness of the sampling calorimeters based on plastic scintillators

Plastic scintillators are very often used as detecting media in sampling calorimeters of High Energy Physics (HEP). Many modern HEP experimental installations are already operating or proposed to work at high luminosity. Plastic scintillators are the most sensitive part of such setups in terms of their radiation hardness. Improving the light collection from the most irradiated scintillators will ensure their long-term use at high luminosity. The experimental results of the measurements for different assemblies (scintillator SCSN-81 and the WLS fiber Y-11 electron-irradiated (E≈4MeV) were obtained. Calculations of the light yields for different samples based on our experimental results show the possibility of increasing the radiation hardness of plastic scintillators inside the sampling calorimeter up to 20Mrad.

Transition radiation detector based on the usage of thin scintillators

Transition Radiation Detector based on the usage of thin scintillators (Sci-TRD) is proposed for particle identification. Such type of TRD may be especially interesting for space apparatus because of no gas. The proposed detector is based on the thin transparent films with incorporated micro-granules of Lu2SiO5:Ce scintillator. Scintillation signal produced by absorbed TR photons is registered by SiPM connected to WLS fibers. Results of measurements with samples of such films are presented. The clear signals from 55Fe (∼5keV) and 241Am (∼16keV) gamma sources were observed. The detailed Monte Carlo simulations of such kind of TRD are also presented.

Scintillator detectors with long WLS fibers and multi-pixel photodiodes

We have studied the possibility of using Geiger mode multi-pixel photodiodes to read out long scintillator bars with a single wavelength-shifting fiber embedded along the bar. This detector configuration can be used in large volume detectors in future long baseline neutrino oscillation experiments. Prototype bars of 0.7 cm thickness and different widths have been produced and tested using two types of multi-pixel photodiodes: MRS APD (CPTA, Moscow) and MPPC (Hamamatsu). A minimum light yield of 7.2 p.e./MeV was obtained for a 4 cm wide bar.

Extensive studies of MRS APDs for plastic scintillator muon veto detectors of cryogenic experiments

Low background experiments need active muon veto detectors to shield them from cosmic muons. Plastic scintillator panels with WLS fiber and multi-pixel Geiger-mode avalanche photodiodes readout are widely used in such experiments due to their compactness and robustness. In this paper, results from the study of the basic MRS APD parameters, such as breakdown voltages, quenching resistors, internal gain and dark count rates are presented, as well as temperature dependencies of some of these parameters. In a small fraction of the MRS APDs, some strange dips in the I–V curves just preceding the breakdown voltage point have been observed.