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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 1.2 A, a background count rate 10 − 3 Hz and a gamma-sensitivity 10 − 6 (measured with a 60Co source), while the dead time is ~20 μs and the multi-count ratio is 1 % . This performance was achieved even for SiPM dark count rates of up to ~2 MHz.

In the work presented here we built and evaluated a single-channel neutron detection unit consisting of a ZnS:$^6$LiF scintillator with embedded WLS fibers readout by a SiPM. The unit has a sensitive volume of 2.4 x 2.8 x 50 mm$^3$; 12 WLS fibers of diameter 0.25 mm are uniformly distributed over this volume and are coupled to a 1 x 1 mm$^2$ active area SiPM. We report the following performance parameters: neutron detection efficiency $\sim 65\,$% at $1.2\,��$, background count rate $< 10^{-3}$ Hz, gamma-sensitivity with $^{60}$Co source $< 10^{-6}$, dead time $\sim 20\,��$s, multi-count ratio $< 1\,$%. All these parameters were achieved up to the SiPM dark count rate of $\sim 2\,$MHz. 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 $\sim 2\,$MHz on the SiPM dark count rate allows to use SiPMs with larger active areas if required., 10 pages, 10 figures

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: 6 LiF 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.

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-RC^4 filter. The performances of the detector with these filters are presented. A full analog signal processing using a CR-RC^4 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.

A small-angle detector will complete the performance of the cold time-of-flight spectrometer FOCUS at the Swiss Spallation Source SINQ of the Paul Scherrer Institute, Villigen, Switzerland. It is constructed from position-sensitive 3He tubes located 2.5 m away from the sample, and covers an area of about 95 × 70 cm2 with a spatial resolution of approximately 1.5 cm. The 2D detector is located within a vacuum chamber, next to the argon chamber of the existing large angle detectors, and covers an angular range from 2 to 22°. Commissioning of the 2D small angle detector will start in spring 2006.

We have developed an ultra-fast multi-channel time-to-digital converter (mC-TDC). The mC-TDC electronics is used to read out the delay-line-based 2-D detectors of the neutron diffractometer and reflectometer TriCS and AMOR, respectively. The high time resolution of the mC-TDC (≈145 ps) allows the conversion of the position-sensitive detector signals into accurate 2-D scattering coordinates (≈2×2 mm2). The mC-TDC also generates low-jitter time-of-flight signals and incorporates an efficient two-stage pileup-rejection mechanism. Neutron rates exceeding 100000 cps can be processed.

Two single channel detection units for thermal neutron detection are investigated in a neutron beam. They consist of two ZnS/${}^6$LiF scintillating layers sandwiching an array of WLS fibers. The pattern of this 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 0.7 MHz, a trigger efficiency of 80% is achieved together with a system background rate lower than ${10}^{-3}$ Hz and a dead time of 30 $\mu$s. No change of performance is observed for neutron count rates of up to 3.6 kHz., Comment: Submitted to Nuclear Instruments and Methods A

A new data acquisition system (DAQ) for bulk μ SR and low-energy μ SR (LE- μ SR) has been developed at PSI. It is based on commercial and in-house VME modules, and on the MIDAS DAQ software library. The system is able to cope with the different needs of the various PSI μ SR spectrometers, which was not possible with the existing CAMAC and ORTEC's pTA-clock based DAQ systems. The VME clock is a 64-channel CAEN V1190 TDC, using the CERN HPTDC chip, with programmable time resolution of 25, 100, 200 or 800 ps. The TDC onboard memory is continuously read through the VME bus by standard PC's or dedicated servers, using a 1-Gbit/s SIS3100/1100 VME–PCI interface. Detector rates are independently monitored using a 32-channel SIS3820 scaler module. In-house developed modules comprise an 8-channel constant fraction discriminator CFD950, a CD950 clock divider, an 8-channel linear fan-out SP950, a 16-channel NIM-ECL level converter LC950, and a programmable coincidence module FC950. All modules feature a superior performance compared to commercially available devices which allows their use also in the planned high-field μ SR spectrometer where a time resolution of about 100 ps is envisaged. A special external hardware logic is no longer required, since the system can deal with a rate total of 5 MHz which is sufficient for μ SR spectrometers with high event rate in their active veto systems.

We report on the possibility of using Silicon Photomultipliers (SiPMs) to detect the scintillation light from neutron conversion in ZnS:6LiF scintillators. The light is collected by wavelength-shifting fibers embedded into the scintillator. The difficulty of extracting neutron signals in the presence of high dark count rates of the SiPMs is addressed by applying a dedicated processing algorithm to analyze the temporal distribution of the SiPM pulses. With a single-channel prototype detection unit we demonstrate a very good neutron signal extraction at SiPM dark count rates of about 1 MHz., Comment: 13 pages, 8 figures; a new section is added, additional discussions and explanations in other sections

Design characteristics and first experience concerning the new high-resolution powder diffractometer for thermal neutrons at the Swiss spallation neutron source SINQ are summarized. It is based on a linear position-sensitive 3 He detector with 1600 wires and angular separation of 0.1°, permitting also real-time experiments.