WLS Fibers Research Articles

A compact neutron detector using scintillators with wavelength shifting fibers by backside readout method

A compact neutron-imaging detector was developed by composition of backside readout method and WLS fibers bended at the right angle. The position resolutions were 0.6 and 0.7 mm for X- and Y-axis, respectively, which were almost as same as that of crossed-fiber readout method. Consequently, a neutron-imaging detector module that has small dead neutron detection area, for example, 15% of the whole front area can be manufactured.

Monte Carlo simulation of different TOF light readout schemes

We report the results of TOF detector resolution studies carried out using a simulation package which takes into account light generation, propagation, attenuation and readout effects. Time resolution has been studied for a classic TOF configuration as well as for the set ups based on light collection via WLS fiber and producing Cherenkov photons. Best resolution has been obtained for the classic TOF configuration.

Auto-triggerable HPD sensors fully readout on ethernet: applications for high-energy physics and medical imaging

The OPERA project is dedicated to neutrino oscillation search in the CNGS neutrino beam from CERN to Gran Sasso (Experimental Proposal, CERN/SPSC 2000-028, SPSC/P318, LNGS P25/2000, July 10, 2000). The experiment is designed to characterize the interactions of ντ resulting of the νμ→ντ oscillation.The main element of the detector is a brick 10.2cm×12.8cm cross-section consisting of 56 emulsion sheets 100μm wide, interleaved with 1mm lead plates. These bricks are assembled in walls of ∼7m side. A total of 72 walls is foreseen for the OPERA experiment with a total fiducial mass of 2ktons.When a neutrino interaction occurs, the tracks of the charged particles are recorded in the emulsions with a high accuracy and the topology of the event is fully reconstructed with an automatic scanning of the emulsions. The role of the target tracker in OPERA is to locate the brick where the primary neutrino interaction occurs, to provide triggers and to make a coarser reconstruction of the events. It consists of two planes of scintillator strips located after a brick wall. The scintillation photons are collected by WLS fibers and read by a multi-pixels photodetector.We present results obtained with 61 pixels HPD's readout by auto-triggerable front-end electronics of the VA–TA series. We have also developed a new kind of acquisition system based on Ethernet, able to read the front-end electronics and deliver the data directly to the Ethernet network. The full readout chain from the scintillator to the DAQ has been tested with cosmics and with beams from the CERN PS.The acquisition scheme is being proposed for the OPERA DAQ system and can be implemented for medical applications with various photodetectors. A prototype of micro-Positron Emission Tomograph (microPET) is being build on this scheme in collaboration with other Rhône–Alpes Institutes.

Photon sandwich detectors with WLS fiber readout

A photon detector for BNL experiment E949 is described. The detector consists of lead/scintillator ``sandwich'' of 25 layers of 5 mm thick scintillator BC404 and 24 layers of 2 mm lead absorber. Readout is implemented with 30-60 cm long WLS fibers (BCF99-29AA) glued into grooves in the BC404. Average yield was measured with cosmic rays to be about 43 p.e./MeV. Extruded plastic scintillation counters developed for sandwich detectors of photons for the KOPIO experiment are also described. For a 7 mm thick counter with 4.3 m long WLS fibers spaced at 7 mm a light yield of 18.7 p.e./MeV and time resolution of 0.71 ns were obtained. A prototype photon veto module consisting of 10 layers of 7 mm thick extruded plastic slabs interleaved with 1 mm lead sheets was tested.

A gamma ray detector with lead-scintillator tiles and WLS fiber readout for the experiment at SPring-8 to study the GDH sum rule

A prototype gamma ray detector for the detection of π 0 in the proposed experiment at SPring-8 to study the Gerasimov–Drell–Hearn (GDH) sum rule (GDH experiment) has been built and tested. The detector is fabricated with lead-scintillator tiles and wave length shifter fiber readout. This detector will be placed inside the bore of the superconducting magnet which supplies the polarized target with a 2.5 T magnetic field. High-detection efficiency (above 85%) for the gamma rays is the most important requirement for this detector to be employed in the proposed experiment. It has been tested with minimum ionizing particles, electrons and gamma rays. The results of the tests in comparison with some Monte Carlo simulations are presented. The evaluated efficiency for gamma rays ranging in energy above 50 MeV is higher than 90%.

Extruded plastic counters with WLS fiber readout

Extruded plastic scintillation counters with WLS fiber readout are described. For a 7 mm thick counter with 4.3 m long double-clad fibers spaced at 7 mm a light yield of 18.7 photoelectrons/MeV and a time resolution of 0.71 ns ( σ) were obtained. A prototype photon veto module consisting of 10 layers of 7 mm thick grooved plastic slabs interleaved with 1 mm lead sheets was also tested, which yielded 122 photoelectrons per minimum ionizing particle and time resolution of 360 ps .

The hadronic calorimeter of the ATLAS experiment at the LHC

I shall report on the final prototype of the hadronic calorimeter being built for the ATLAS experiment at LHC. This calorimeter is made of iron and scintillating tiles. Light collection is realized with WLS fibers. The projective geometry of the calorimeter is obtained by properly grouping fibers which are then readout with photomultipliers. The main characteristics of the three main components of the calorimeter, i.e. scintillating tiles, WLS fibers and photomultipliers will be described together with the performance of the calorimeter prototype (resolution and linearity) as measured in test beam both in “standalone” configuration and in combination with the ATLAS electromagnetic calorimeter.

Performance of the ZEUS forward plug calorimeter

With the installation of a forward plug calorimeter (FPC) the calorimetric coverage of the ZEUS detector has been extended by one unit in pseudorapidity (ZEVS FPC group, Nucl. Instr. and Meth., in print). The FPC is a compensating shashlik-type calorimeter with layers of 15 mm thick Pb and 2.6 mm thick organic scintillators. The light is read out with WLS fibers and PMTs. Before installation in ZEUS the FPC has been tested and calibrated with test beams of 10– 100 GeV . Long-term stability is monitored with a 60Co source.

Recent results on radiation hardness tests of WLS fibers for the ATLAS Tilecal hadronic calorimeter

Three types of fibers, that were candidates to be used in the Tilecal/ATLAS detector were irradiated in a 60 Co γ source. The degradation of the light output and attenuation length were measured a few hours and several days after the end of the irradiation. The results are presented.

Application of avalanche photodiodes as a readout for scintillator tile–fiber systems

The application of reach-through avalanche photodiodes (R'APD) as a photodetector for scintillator tiles has been investigated. The light collected by WLS fibers (0.84 and 1 mm diameter) embedded in the scintillator has been transmitted to the 0.5 mm 2 active surface of APD by clear optical fibers and optical connectors. A low noise charge sensitive preamplifier (≈400e − equivalent noise charge) has been used to amplify the photodiode signal. Various configurations of tile–fiber systems, suitable for CMS and LHCb experiments at LHC have been studied using cosmic muons and muon beam at SPS at CERN. In order to optimize the performance of APD, measurements in the temperature range from −10°C to +25°C have been made. The MIP detection efficiency and e −/MIP separation have been estimated in order to determine applicability of the readout for LHCb preshower.

Application of avalanche photodiodes as a readout for scintillator tile-fiber systems

The application of reach-through avalanche photodiodes (R'APD) as a photodetector for scintillator tiles has been investigated. The light collected by WLS fibers (0.84mm and 1mm diameter) embedded in the scintillator has been transmited to the 0 .5mm2 active surface of APD by clear optical fibers and optical connectors. A low noise charge sensitive preamplifier (approximately 400 electrons equivalent noise charge) has been used to gain the photodiode signal. Various configurations of tile-fibre s ystems, suitable for CMS and LHCb experiments at LHC have been studied using cosmic muons and muon beam at SPS at CERN. In order to optimize the performance of APD, measurments in the temperature range from -10°C to +25°C have been done. The MIP detection efficiency and electron/MIP separation have been estimated in order to determine applicability of the readout for LHCb preshower.

Readout optimization for the KLOE QCAL tile calorimeters

A tile calorimeter (QCAL) has been designed for the KLOE experiment. Optimization studies have been conducted by testing the coupling between different types of scintillators and WLS fibers. Results on light yield, attenuation length of fibers and time resolution are presented.

Dose rate effects in WLS fibers

The radiation hardness of different types of WLS fibers produced by BICRON, KURARAY and POL.HI.TECH has been systematically studied. Low dose rate irradiations (from 0.55 krad/h up to 4 krad/h and total dose of about 140 krad) were performed with a 60Co γ source. The results are compared with high dose rate irradiations (1.5 Mrad/h and total dose of 1 Mrad) in a mixed field of 20% of neutrons and 80% of γ's in a nuclear reactor. The degradation of the optical properties of fibers with different composition, namely different Ultraviolet absorber (UVA) concentration and different type of cladding are studied. Dose rate effects are investigated as well as the effect of irradiation with different type of particles. The UVA can help on the radiation hardness, but no permanent dose rate effects, or special effects due to the neutron component of the irradiation field were observed.

State of art of (green) wavelengthshifting fibers

Comparative studies of the optical properties of polystyrene WLS fibers for High Energy Physics Experiments are presented. The response of fibers to the blue light of a plastic scintillator is compared for fibers with different dopant concentration, with single and multiple cladding, and with several Ultra Violet Absorbers (UVA) with different concentrations. Preliminary results on the mechanical stress of the fibers are shown and a brief summary of the radiation hardness is given.

The HERA-B electromagnetic calorimeter

We present test results on the HERA-B electromagnetic calorimeter modules. The module design exploits the “shashlik” technology of the light readout by means of wavelength shifting fibers. Results of R&D on the calorimeter inner section including radiation tests of module parts (scintillator, WLS fibers and PMs), measurements of scintillator-fiber light yield and tests of the module prototype at the electron beam are presented. For the modules of the middle section we present results on energy and position resolution measured with electrons in the momentum range 1–5 GeV/ c. The response uniformity and cell-to-cell reproducibility have been studied with MIP at the ITEP accelerator. Results of beam tests are compared with a Monte Carlo simulation.

Low dose rate evaluations of long plastic scintillator plates and Bicron G2-doped wavelength shifting fibers

Electromagnetic calorimeter modules are being constructed for the CEBAF Large Acceptance Spectrometer that will utilize plastic plate scintillators that can be over 4 meters in length. At shower maximum, it is expected that up to 100 Gray may be deposited over a ten year lifetime in the detector elements. Although it is believed that PVT-based scintillators are radiation-hard at that level, the large size of the plates motivated an ageing test of a 2 meter long sample so as to gain a realistic estimate of the loss in intrinsic light output and especially in attenuation performance of the chosen scintillator (Bicron BC412). A test setup was designed so that the sample was irradiated (by a /sup 60/Co line source) at a rate sufficiently low (0.5 Gray/hr) to allow complete diffusion of oxygen into the material during the irradiation. Additionally, in order to ensure complete diffusion and to gain a pessimistic estimate of damage, a pure oxygen atmosphere was circulated through the sample container during the irradiation, and the total dose was increased to a total of 160 Gray. Within the same setup, tests were also made of two additional materials: (1) a 1 meter long sample of an uniquely bright, fast green scintillator with superior attenuation properties, and (2) a customized acrylic scintillator (with a high doping level of fluors) read out by embedded (into smooth grooves cut into the surface of the scintillator) wavelength shifting fibers doped with the same green fluor as the aforementioned scintillator. The data indicates that the BC412 shows no loss in intrinsic light output, but does have an attenuation loss amounting to 10% at 1 meter and 16% at 2 meters. The fast green scintillator (and fibers) showed no damage. When read out by WLS fibers, the acrylic scintillator displayed a loss in intrinsic light output, but no change in attenuation. >

Low Dose Rate Tests of Plastic Scintillator Plates and Wavelength Shifting Fibers

ABSTRACTA low dose rate evaluation of several scintillators and wavelength shifters of interest to the CEBAF program was performed with a 60Co line source to a total dose of 160 Gray at a rate of 0.5 Gy/hr in a slowly flowing oxygen atmosphere. The samples included the following: (1) a 2 meter piece of Bicron BC412 scintillator being extensively used in the CEBAF Large Acceptance Spectrometer, (2) a 1 meter long piece of green scintillator doped with a uniquely fast green fluor (G2), (3) wavelength shifting fiber dopedalso with G2, and (4) grooved acrylic-based scintillator that is readout with the WLS fiber. The data indicates that the BC412 shows no loss in intrinsic light output, but does have an attenuation loss amounting to 10% at 1 meter and 16% at 2 meters. The fast green scintillator (and fibers) showed no damage. When read out by WLS fibers, the acrylic scintillator displayed a loss in intrinsic light output, but no change in attenuation.