Position-sensitive Neutron Detector Research Articles

Development of fusion neutron camera using organic liquid scintillator and wavelength shifting fiber

For fusion neutron profile monitoring, we propose to use a new position sensitive fast neutron detector (PSFND). We have considered an applicability of the present PSFND to two types of fusion neutron camera; a pinhole camera and a double crystal time-of-flight camera.

A gas proportional scintillator counter for thermal neutrons instrumentation

A gaseous scintillation detector consisting of a 3 He+CF 4 filled MSGC detector coupled with an optical readout has been investigated for an application for high-resolution and high counting rate position-sensitive neutron detector. Measurements of the photons' emission as a function of the gas mixture have been carried out indicating that filling the detector with 3 He+CF 4 is a very good choice also from the point of view of optical readout and not only for charge readout. The light yield has been systematically measured as a function of the CF 4 concentration and operating voltages. We also studied the emission of primary light, rather strong in CF 4 mixtures, which allows the observation of the light signal even in the absence of high voltage on the electrodes. Finally, some measurements of the position resolution will be presented.

Two-dimensional position sensitive neutron detector

A two-dimensional position sensitive neutron detector has been developed. The detector is a3He + Kr filled multiwire proportional counter with charge division position readout and has a sensitive area of 345 mm × 345 mm, pixel size 5 mm × 5 mm, active depth 25 mm and is designed for efficiency of 70% for 4 A neutrons. The detector is tested with 0.5 bar3He + 1.5 bar krypton gas mixture in active chamber and 2 bar4He in compensating chamber. The pulse height spectrum recorded at an anode potential of 2000 V shows energy resolution of ∼25% for the 764 keV peak. A spatial resolution of 8 mm × 6 mm is achieved. The detector is suitable for SANS studies in theQ range of 0.02-0.25 A−1.

Development of position-sensitive neutron detector based on scintillator

For evaluating neutron optical devices, we have developed the two-dimensional position-sensitive neutron detectors (PSND) of the crossing fibre array type. In parallel, we have studied the PSNDs of the direct coupling type with flat panel photomultiplier tubes for responding to various spatial resolutions with high detection efficiency. This paper views and reports on the recent status of development of PSNDs based on neutron scintillators in neutron optics group.

Preparation of thin-film neutron converter foils for imaging detectors

With the pending delivery of the new Spallation Neutron Source at Oak Ridge National Laboratory, a new generation of highly efficient, position sensitive neutron detectors needs to be developed. One promising prospect for detector development has been the neutron imaging detector consisting of a conversion foil, which produce amongst other things /spl alpha/ and /spl gamma/ particles from incident neutrons, and a position sensitive charge particle detector. In order to understand the materials chemistry between layered converters as well as to maximize the production and transmission of the daughter products, we have prepared and characterized a series of thin-films from naturally occurring isotopes of the strong neutron absorbers lithium (Li), boron (B), and gadolinium (Gd). The films have been created using a combination of sputtering and evaporation techniques. The composition of the resulting films have been investigated using EDS and RBS, while the interfacial mixing between the layers has been studied using a combination of RBS and SEM experiments. Experiments studying the aging of the detector films in the detector gas as well as alloying of Li and the film substrate, have also been undertaken and the results are reported here.

Measurements of performance of a pixel-type two-dimensional position sensitive Li-glass neutron detector

We have developed a pixel-type two-dimensional position sensitive Li-glass neutron detector for high rate application, which would be useable for time-of-flight radiography, namely transmission spectroscopy. The pieces of Li-glass were attached directly to a 8×8 channel photo multiplier. We measured its performance at KEK and Hokkaido University. The count rate of this detector was found to be about 8.3 Mcps/cm 2 (240 Kcps per pixel). The efficiency of the detector corrected for the effective detection area is 100% over 9 Å and 95% at 3 Å. The difference in the count rate of each pixel was very small, less than 2%.

Current status and future directions of position sensitive neutron detectors at ISIS

Position sensitive detectors at the ISIS facility largely comprise of a mixture of 3He proportional counters and fibre-coded scintillation detectors based on ZnS/ 6LiF. The latest developments of these devices at ISIS will be discussed with reference to three ISIS instruments, MERLIN, GEM and ENGIN-X. MERLIN is the new chopper spectrometer now being developed at ISIS and features a large 2D detector array covering more than 20 m 2 with a requirement in position resolution of 25×25 mm 2. Resistive wire detectors are proposed for this detector, but to minimise gaps in the solid angle, detectors with active lengths of 2.9 m are being proposed. Initial results from prototype detectors will be presented. GEM is a general materials diffractometer now nearing completion and ENGIN-X is the engineering instrument, which became operational in November 2002. Detectors for both these instruments use linear arrays of fibre optic-encoded ZnS/ 6Li scintillator, with position resolutions of 5 and 3 mm, respectively. Work has now started on the construction of the ISIS second target station, TS-2. This facility will be tailored to the production of lower-energy neutrons compared with target station 1, with applications predominantly in soft condensed matter, bio-molecular sciences and advanced materials. The challenges this presents for future neutron detector development at ISIS will be reviewed together with some potential lines of detector development.

Development status of position-sensitive neutron detectors for J-PARC in JAERI—a comprehensive overview

We have developed various kinds of position-sensitive neutron detectors in JAERI for the J-PARC project. The neutron imaging detectors using scintillators have been developed aiming for high counting rate, high spatial resolution, high neutron gamma-rays discrimination, and high detection efficiency. The development included various kinds of phosphors, scintillators, and read-out methods. Another is a two-dimensional gaseous neutron detector, which is based on a microstrip technology. The development of the microstrip gas chamber that has individual strip read-out and of the instrument system with a capability of secondary-particle discrimination is underway for a high spatial resolution and high detection efficiency with moderate area coverage.

Current status and future directions of position sensitive neutron detectors at ISIS

Position sensitive detectors at the ISIS facility largely comprise of a mixture of 3 He proportional counters and fibre-coded scintillation detectors based on ZnS/ 6 LiF. The latest developments of these devices at ISIS will be discussed with reference to three ISIS instruments, MERLIN, GEM and ENGIN-X. MERLIN is the new chopper spectrometer now being developed at ISIS and features a large 2D detector array covering more than 20 m 2 with a requirement in position resolution of 25×25 mm 2 . Resistive wire detectors are proposed for this detector, but to minimise gaps in the solid angle, detectors with active lengths of 2.9 m are being proposed. Initial results from prototype detectors will be presented. GEM is a general materials diffractometer now nearing completion and ENGIN-X is the engineering instrument, which became operational in November 2002. Detectors for both these instruments use linear arrays of fibre optic-encoded ZnS/ 6 Li scintillator, with position resolutions of 5 and 3 mm, respectively. Work has now started on the construction of the ISIS second target station, TS-2. This facility will be tailored to the production of lower-energy neutrons compared with target station 1, with applications predominantly in soft condensed matter, bio-molecular sciences and advanced materials. The challenges this presents for future neutron detector development at ISIS will be reviewed together with some potential lines of detector development.

Recent development of position-sensitive neutron detectors employing wavelength-shifting cross-fiber

For evaluating neutron optical devices, we have designed and tested two-dimensional position-sensitive neutron detectors (PSND) which employ two wavelength-shifting fiber arrays optically coupled to a scintillator plate. Feasibility on applications of the PSND having a 50×50 mm 2 sensitive area and a pixel size of 0.4×0.4 mm 2 has been tested at pulsed neutron sources. While, for realizing the large sensitive area, another PSND having a 128×128 mm 2 sensitive area and a 0.5×0.5 mm 2 pixel size with a dynode coding technique were developed and tested.

Resolving pile up with a real-time processor for delay line detectors

We report on the upgrade of a position-sensitive neutron detector for the D17 neutron reflectometer at the ILL Grenoble. The maximum count rate of this instrument has been increased to 420 kHz without sacrifice of spatial resolution. Using a multi-hit Time-to-Digital Converter and a RISC VME processor, we have implemented a real-time position reconstruction algorithm which improves the detector efficiency by recovering piled-up neutrons. The analysis relies on software cathode time checksums, thus avoiding position-dependent inefficiencies and reconstruction errors.

Time analysis of the light pulses on gaseous active scintillators using GEMs with He/CF4

The time structure of light pulses from GEM detectors operated in scintillation mode with He/CF4 mixtures, previously used with integrating readout devices for neutron detection, has been investigated. A system using photomultipliers (PMs) and charge preamplifiers coupled to a fast digitizer has been used to measure simultaneously both the charge and light signals of the avalanches and the dependence of these signals on the operating conditions of the GEM, such as gain, transfer yield and collection field. The present results show that detectors relying on photon counting techniques, using of position sensitive PMs or arrays of avalanche photodiodes, are most promising as fast position sensitive neutron detectors.

Sub-nanosecond multi-channel time-to-digital converter for the 2-D position-sensitive neutron detectors at TriCS and AMOR

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.

A high-luminosity position sensitive neutron detector for residual stress measurements

Because the diffraction angle is equal or close to 90/spl deg/ in residual stress measurements by neutron diffraction, the luminosity of the device can be increased by expansion of the detection window height without deformation of the diffraction peak. A high luminosity position sensitive neutron detector has been designed and fabricated for measuring residual stress. The detector has a working window of 200 /spl times/ 100 mm/sup 2/. The detector has high efficiency, good position resolution and linearity, small position error and low background counts. The results of the detector characteristics are presented.

Fast two-dimensional position-sensitive detection of neutrons in a time-of-flight reflectometer

A two-dimensional position-sensitive neutron detector with a maximum count rate of 500kHz is described. The high counting rate is obtained by making use of dedicated electronics for data handling. The electronics convert the wire charges of a position-sensitive photomultiplier into a position using internal look-up tables. Timing modules are presented for neutron time-of-flight (TOF) determination and for dynamic measurements with an independent time-base. The position and TOF information are stored by a fast Data Handling Module. The detector is calibrated with a grid of 256×256 channels, using channel widths of 0.25mm.The maximum error in position determination is 0.25mm.This error is reduced to less than 0.05mm when the electronics are used one dimensionally instead of two dimensionally. The total detector resolution was determined to be 0.6mm.

A large, high performance, curved 2D position-sensitive neutron detector

A new position-sensitive neutron detector has been designed and constructed for a protein crystallography station at LANL's pulsed neutron source. This station will be one of the most advanced instruments at a major neutron user facility for protein crystallography, fiber and membrane diffraction. The detector, based on neutron absorption in 3He, has a large sensitive area of 3000 cm 2 , angular coverage of 120°, timing resolution of 1 μs , rate capability in excess of 10 6 s −1 , position resolution of about 1.5 mm FWHM, and efficiency >50% for neutrons of interest in the range 1– 10 A ̊ . Features that are key to these remarkable specifications are the utilization of eight independently operating segments within a single gas volume, fabrication of the detector vessel and internal segments with a radius of curvature of about 70 cm , optimized position readout based on charge division and signal shaping with gated baseline restoration, and engineering design with high-strength aluminum alloy.

Position-sensitive neutron detector

A position-sensitive neutron detector has been developed for use in nuclear physics research. The detector consists of a ∅5.5 cm×100 cm long quartz tube filled with liquid scintillator viewed from both ends by photomultipliers and enclosed in a light-tight titanium container. The properties of the detector were determined both experimentally and by Monte Carlo simulations (EFEN code). A time resolution of 0.4 ns was reached resulting in the position resolution of less than 4 cm. The neutron registration efficiency varies from 36% to 20% within neutron energy range 1–10 MeV and is practically independent of the position along the detector length. Good n–γ separation is achieved for neutron energies greater than 0.5 MeV.

Front-end electronics for high rate, position sensitive neutron detectors

Advanced neutron detectors for experiments at new spallation sources will require greater counting rate capabilities than previously attainable. This necessitates careful design of both detector and readout electronics. As part of a new instrument for protein crystallography at LANSCE, we are constructing a detector whose concept was described previously (IEEE Trans. Nucl. Sci. NS-46 (1999) 1916). Here, we describe the signal processing circuit, which is well suited for 3He detectors with a continuous interpolating readout. The circuit is based on standard charge preamplification, transmission of this signal over 20 meters or so, followed by sample and hold using a second order gated baseline restorer. This latter unit provides high rate capability without requiring pole-zero and tail cancellation circuits. There is also provision for gain-adjustment. The circuits are produced in surface mounted technology.

Two-dimensional position-sensitive detectors for high resolution diffraction with neutrons and high energy synchrotron radiation

A two dimensional position-sensitive neutron detector has been developed at the Geesthacht Neutron Facility (GeNF) for the new diffractometer ARES which is dedicated to the analysis of residual stresses. The detector is a 3He and CF 4 filled multiwire proportional counter with delay line readout and has a sensitive area of 300 mm×300 mm.The detector was tested at different 3He and CF 4 partial pressures with a well collimated neutron beam. Excellent linearity and homogeneity of the detection probability combined with a spatial resolution of about 2 mm×2 mm were found.

A position-sensitive ionization chamber for thermal neutrons

A position-sensitive neutron detector based on /sup 3/He is being developed for a national crystal backscattering spectrometer (CBS) at a pulsed neutron source. It comprises a single gas volume, of constant depth, in the form of an annulus that is also part of a truncated cone. Charge from each event is collected on one or two anode strips, out of a total 336 around the annulus, yielding an angular resolution of about 1/spl deg/. Low-noise signal processing, in the form of a monolithic preamplifier/shaping amplifier connected to each anode strip, provides electronic noise that is small enough to permit detector operation in an ionization mode. In addition, the segmented anodes ensure near complete induced charge collection. This new detector therefore has significant advantages over previous detectors used in CBS instruments, which primarily consisted of arrays of individual /sup 3/He filled cylindrical counters with dead regions and nonuniform detection efficiency. The optimization of gas mixture/pressure, drift field, and shaping time is significant in achieving successful performance in the new detector.