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Register a new userSilicon photomultiplier readout of a monolithic 270$times$5$times$5 cm$^3$ plastic scintillator bar for time of flight applications
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The detection of 200-1000 MeV neutrons requires large amounts, $sim$100 cm, of detector material because of the long nuclear interaction length of these particles. In the example of the NeuLAND neutron time-of-flight detector at FAIR, this is accomplished by using 3000 monolithic scintillator bars of 270$times$5$times$5 cm$^3$ size made of a fast plastic. Each bar is read out on the two long ends, and the needed time resolution of $sigma_t$ $<$ 150 ps is reached with fast timing photomultipliers. In the present work, it is investigated whether silicon photomultiplier (SiPM) photosensors can be used instead. Experiments with a picosecond laser system were conducted to determine the timing response of the assembly made up of SiPM and preamplifier. The response of the full system including also the scintillator was studied using 30 MeV single electrons provided by the ELBE superconducting electron linac. The ELBE data were matched by a simple Monte Carlo simulation, and they were found to obey an inverse-square-root scaling law. In the electron beam tests, a time resolution of $sigma_t$ = 136 ps was reached with a pure SiPM readout, well within the design parameters for NeuLAND.
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The performance of scintillator counters with embedded wavelength-shifting fibers has been measured in the Fermilab Meson Test Beam Facility using 120 GeV protons. The counters were extruded with a titanium dioxide surface coating and two channels for fibers at the Fermilab NICADD facility. Each fiber end is read out by a 2*2 mm^2 silicon photomultiplier. The signals were amplified and digitized by a custom-made front-end electronics board. Combinations of 5*2 cm^2 and 6*2 cm^2 extrusion profiles with 1.4 and 1.8 mm diameter fibers were tested. The design is intended for the cosmic-ray veto detector for the Mu2e experiment at Fermilab. The light yield as a function of the transverse and longitudinal position of the beam will be given.
Recent tests of a single module of the Jagiellonian Positron Emission Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips have proven its applicability for the detection of annihilation quanta (0.511 MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved resolution is almost by a factor of two better with respect to the current TOF-PET detectors and it can still be improved since, as it is shown in this article, the intrinsic limit of time resolution for the determination of time of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much lower. As the major point of the article, a method allowing to record timestamps of several photons, at two ends of the scintillator strip, by means of matrix of silicon photomultipliers (SiPM) is introduced. As a result of simulations, conducted with the number of SiPM varying from 4 to 42, it is shown that the improvement of timing resolution saturates with the growing number of photomultipliers, and that the 2 x 5 configuration at two ends allowing to read twenty timestamps, constitutes an optimal solution. The conducted simulations accounted for the emission time distribution, photon transport and absorption inside the scintillator, as well as quantum efficiency and transit time spread of photosensors, and were checked based on the experimental results. Application of the 2 x 5 matrix of SiPM allows for achieving the coincidence resolving time in positron emission tomography of $approx$ 0.170 ns for 15 cm axial field-of-view (AFOV) and $approx$ 0.365 ns for 100 cm AFOV. The results open perspectives for construction of a cost-effective TOF-PET scanner with significantly better TOF resolution and larger AFOV with respect to the current TOF-PET modalities.
A laser calibration system was developed for monitoring and calibrating time of flight (TOF) scintillating detector arrays. The system includes setups for both small- and large-scale scintillator arrays. Following test-bench characterization, the laser system was recently commissioned in experimental Hall B at the Thomas Jefferson National Accelerator Facility for use on the new Backward Angle Neutron Detector (BAND) scintillator array. The system successfully provided time walk corrections, absolute time calibration, and TOF drift correction for the scintillators in BAND. This showcases the general applicability of the system for use on high-precision TOF detectors.
Plastic scintillation detectors for Time-of-Flight (TOF) measurements are almost essential for event-by-event identification of relativistic rare isotopes. In this work, a pair of plastic scintillation detectors of 50 $times$ 50 $times$ 3$^{t}$ mm$^3$ and 80 $times$ 100 $times$ 3$^{t}$ mm$^3$ have been set up at the external target facility (ETF), Institute of Modern Physics. Their time, energy and position responses are measured with $^{18}$O primary beam at 400 MeV/nucleon. After the off-line walk-effect and position corrections, the time resolution of the two detectors are determined to be 27 ps ($sigma$) and 36 ps ($sigma$), respectively. Both detectors have nearly the same energy resolution of 3$%$ ($sigma$) and position resolution of 2 mm ($sigma$). The detectors have been used successfully in nuclear reaction cross section measurements, and will be be employed for upgrading RIBLL2 beam line at IMP as well as for the high energy branch at HIAF.
Silicon Photo-Multipliers (SiPM) are becoming the photo-detector of choice for increasingly more particle detection applications, from fundamental physics to medical and societal applications. One major consideration for their use at high-luminosity colliders is the radiation damage induced by hadrons, which leads to a dramatic increase of the dark count rate. KETEK SiPMs have been exposed to various fluences of reactor neutrons up to $Phi_{neq}$ = 5$times$10$^{14}$ cm$^{-2}$ (1 MeV equivalent neutrons). Results from the I-V, and C-V measurements for temperatures between $-$30$^circ$C and $+$30$^circ$C are presented. We propose a new method to quantify the effect of radiation damage on the SiPM performance. Using the measured dark current the single pixel occupation probability as a function of temperature and excess voltage is determined. From the pixel occupation probability the operating conditions for given requirements can be optimized. The method is qualitatively verified using current measurements with the SiPM illuminated by blue LED light.
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