Linear Position-sensitive Detector Research Articles

Performance of small- and wide-angle x-ray scattering beamline at Indus-2 synchrotron

A Small- and Wide-Angle X-ray Scattering (SWAXS) beamline (BL-18) is installed and commissioned at a 1.5 T bending magnet port (5°) of Indus-2 synchrotron at RRCAT, Indore, India. The ∼40-m-long beamline has tunable x-ray energy in the range of 5–20 keV by using a double crystal monochromator. A 1.5-m-long toroidal mirror is used to focus the x-ray beam at the detector position. The beamline is equipped with a 6-m-long movable detector stage to access different wave-vector transfer ranges. At present, an online image plate area detector and a linear position-sensitive gas detector are installed for Small-Angle X-ray Scattering (SAXS) and Wide-Angle X-ray Scattering (WAXS) measurements, respectively. The beamline is operational in simultaneous SAXS/WAXS mode to probe the mesoscopic as well as molecular level structure over a wide range of wave-vector transfer. The specification of the beamline and its performance are reported here. A few recent experimental results, as obtained from BL-18, are also described in brief.

Development of 3He-filled linear position-sensitive detector for neutron scattering instruments at CSNS

Development of 3He-filled linear position-sensitive detector for neutron scattering instruments at CSNS

The NOMAD instrument neutron detector array at the SNS

The neutron detector array for the Nanoscale-Ordered Materials Diffractometer instrument at the Spallation Neutron Source is discussed. The instrument employs a unique arrangement of helium-3 filled, linear position sensitive detectors in three distinct modular packages. Instrument specific requirements that lend to the unique detector design are discussed herein. This paper focuses on the mechanical design of the detector array, detector tube design, and specific detector performance aspects. Additionally, a general overview of helium-3 linear position sensitive detector physics, associated signal processing methods, and acceptance testing criteria are presented.

Multiple Wavelengths Texture Measurement Using Angle Dispersive Neutron Diffraction at WOMBAT

In contrast to conventional angle dispersive neutron diffractometers with a single-tube detector or a small-size linear position-sensitive detector, the WOMBAT diffractometer of the Australian Nuclear Science and Technology Organisation (ANSTO) is equipped with a large-area curved position-sensitive detector, spanning 120° for the scattering angle 2θ and 15° for the azimuth η, respectively. Here, WOMBAT was employed in establishing a texture measurement environment for complex textured samples, through measuring neutron diffractograms at two selected wavelengths on a typical reference sample of martensite–austenite multilayered steel sheet. All neutron patterns were simultaneously Rietveld analyzed using the software, Materials Analysis Using Diffraction (MAUD). The shorter wavelength (λ1 = 1.54 Å, k1 = 4.08 Å−1) enabled collecting the martensite reflections α-110, α-200, α-211, α-220, α-310, and α-222, as well as the austenite peaks γ-111, γ-200, γ-220, γ-311, γ-222, and γ-331 simultaneously, by pre-setting the detector range to 2Θ = 30~150°. The longer wavelength (λ2 = 2.41 Å, k2 = 2.61 Å−1) enabled separating the overlapping strong martensite α-110 and austenite γ-111 Laue–Bragg interferences more reliably. Moreover, the detector panel division along the vertical direction has a good stereographic coverage in the azimuthal angle η,. Such a combination of multiple-wavelength neutron diffraction combined with simultaneous Rietveld texture analysis was confirmed as being very valuable for realizing high precision measurements for complex textured samples at an orientation distribution graticule of 5°, and in a much shorter beam time than the conventional angle dispersive method.

Enhanced position resolution for ZnS:Ag/^6LiF wavelength shifting fibre thermal neutron detectors

The high neutron intensity, improvements in neutron delivery and increasingly more complex experiments at neutron scattering facilities, i.e. J-PARC, SNS, ISIS, CSNS and ESS, which is presently under construction, drive the development of neutron scattering instruments and their associated detectors. High position resolution is one of the most demanding detector requirements and is particularly relevant of neutron reflectometry applications. Scintillator detectors using ZnS:Ag/^6LiF coupled to wavelength shifting fibre (WLSF) are currently employed in several neutron scattering facilities, including J-PARC, SNS, ISIS and CSNS. For WLSF-based scintillation detectors, the position reconstruction is routinely achieved by determining the combination of fibres that absorb scintillation light. The use of position reconstruction algorithms, analysing light spread in the system, leads to an increase in the position resolution. The optimisation of a centre of gravity interpolation method for linear position-sensitive detectors has been developed, and a factor 2 improvement in position sensitivity has been achieved. The investigation of the light spread over the fibres and the detector performance in correlation with the reconstructed position resolution are discussed.

The Large-Area Detector for Small-Angle Neutron Scattering on iMATERIA at J-PARC

An area detector with a central hole structure was built up for small-angle neutron scattering (SANS) on the iMATERIA instrument at Japan Proton Accelerator Research Complex (J-PARC). Linear position-sensitive detector tubes filled with 3He gas were arranged in three layers leaving a central hole. As a result of the calibration process, a SANS measurement with wide q-range from 0.007 Å−1 to 4.3 Å−1 was achieved in double-frame operation, supplying neutrons with wavelengths from 1 Å to 10 Å. As a merit of this central hole structure, neutron transmission can be measured simultaneously to reduce experimental time and effort. This is ideal for time-resolved studies, in which the sample transmission can be time-dependent, throughout the whole experiment. Additionally, the data storage system in ‘event mode’ format provides an excellent platform for such time-resolved experiments.

Improved neutron-gamma discrimination for a 3He neutron detector using subspace learning methods

3He gas based neutron Linear-Position-Sensitive Detectors (LPSDs) have been used for many neutron scattering instruments. Traditional Pulse-height Analysis (PHA) for Neutron-Gamma Discrimination (NGD) resulted in the neutron-gamma efficiency ratio (NGD ratio) on the order of 105–106. The NGD ratios of 3He detectors need to be improved for even better scientific results from neutron scattering. Digital Signal Processing (DSP) analyses of waveforms were proposed for obtaining better NGD ratios, based on features extracted from rise-time, pulse amplitude, charge integration, a simplified Wiener filter, and the cross-correlation between individual and template waveforms of neutron and gamma events. Fisher Linear Discriminant Analysis (FLDA) and three Multivariate Analyses (MVAs) of the features were performed. The NGD ratios are improved by about 102–103 times compared with the traditional PHA method. Our results indicate the NGD capabilities of 3He tube detectors can be significantly improved with subspace-learning based methods, which may result in a reduced data-collection time and better data quality for further data reduction.

X-ray diffraction and NMR data for the study of the location of idebenone and idebenol in model membranes.

Here we present some of our data about the interaction of idebenone and idebenol with dipalmitoyl-phosphatidylcholine (DPPC). In particular, we include data of small angle X-ray diffraction (SAXD) and wide angle X-ray diffraction experiments, obtention of electronic profiles of the membranes, 2H-NMR and 31P-NMR, as part of the research article: “Both idebenone and idebenol are localized near the lipid-water interface of the membrane and increase its fluidity” (Gomez-Murcia et al., 2016) [1]. These data were obtained from model membranes that included different proportions of idebenone and idebenol, at temperatures both above and below of the gel to fluid phase. The X-ray experiments were carried out by using a modified Kratky compact camera (MBraun-Graz-Optical Systems, Graz Austria), incorporating two coupled linear position sensitive detectors. The NMR data were collected from a a Bruker Avance 600 instrument.

Corrections for the geometric distortion of the tube detectors on SANS instruments at ORNL

The small-angle neutron scattering instruments at the Oak Ridge National Laboratory׳s High Flux Isotope Reactor recently upgraded the area detectors from the large, single volume crossed-wire detectors originally installed to staggered arrays of linear position-sensitive detectors (LPSDs). The specific geometry of the LPSD array requires that approaches to data reduction traditionally employed be modified. Here, two methods for correcting the geometric distortion produced by the LPSD array are presented and compared. The first method applies a correction derived from a detector sensitivity measurement performed using the same configuration as the samples are measured. In the second method, a solid angle correction is derived that can be applied to data collected in any instrument configuration during the data reduction process in conjunction with a detector sensitivity measurement collected at a sufficiently long camera length where the geometric distortions are negligible. Both methods produce consistent results and yield a maximum deviation of corrected data from isotropic scattering samples of less than 5% for scattering angles up to a maximum of 35°. The results are broadly applicable to any SANS instrument employing LPSD array detectors, which will be increasingly common as instruments having higher incident flux are constructed at various neutron scattering facilities around the world.

Preferred Orientation, PDF and Debye Equation

The effect of preferred orientation is currently neglected in the Debye Equation and PDF calculations. This is to a large extend justified, especially for the PDF, as the scattering by large sample volumes is detected by an area detector. The integration of powder rings reduces the effects of preferred orientation. As more laboratory PDF measurements become available that use linear position sensitive detectors or single counter detectors, preferred orientation needs to be reconsidered. A Rietveld calculation treats preferred orientation by multiplying the Bragg intensity by a factor that depends on the angle between the reciprocal space vector and the preferred orientation axis. The powder intensity I(Q) is thus multiplied by a complex function that depends at each Q on the degree of preferred orientation, the lattice parameters, reflection multiplicity etc. The effect on the PDF is therefore the convolution by the Fourier transform of this complex function. The Debye equation is derived from a spherical average of the scattering intensity of a finite object. Thus completely random orientation of the powder grains is implicitly assumed. Both, the Debye algorithm and the PDF algorithm calculate the powder pattern, respectively the PDF from a histogram of interatomic distances, which correspond to a spherical average of all interatomic distance vectors. This histogram does not allow for a Rietveld preferred orientation correction. The effects of preferred orientation on the PDF will be presented on the basis of simulated diffraction pattern. An algorithm to describe the changes in the PDF and the inverse sine Fourier transform as a convenient tool to calculate the powder diffraction pattern will be introduced. This is a good alternative to the Debye equation and allows to take preferred orientation into account both for the PDF and the calculated powder.

Investigation of layered double hydroxides type ZnMgAl-carbonate and derivates.

Layered double hydroxides (LDHs) or hydrotalite-like compounds belong to a class of synthetic two-dimensional inorganic materials with lamellar structures, where the hydroxyl-hydrated compounds are formed by chemical substitution of divalent ion of the brucite-like octahedral layers by trivalent ions [1]. The LDH are represented by the general formula, Figure a , where M2+, M3+ are divalent and trivalent cation and Am- is interlayer anion responsible by charge balancing, the range of divalent and trivalent ions (x) varies normally between 0.17 a 0.33. According Montanari and co-works [2] compounds type ZnAl-hydrotalcites (ZnAl-HT) have relevant industrial interest; however the scientific literature concerning this material as catalysts or catalyst precursor is scarce. Based on this fact, in the present communication we will present a studied on how the variation in percentage of Zinc in a ZnMgAl-HT catalyst precursor can influence the formation of mixed oxides after calcination. The ZnMgAl-HTs, Figure b , y=5, 10,15,20,25,50,75 and 100% were prepared by co-precipitation and urea method. Mg-Zn/Al mixed oxides were prepared from calcinations of hydrotalcites precursors at 5000C for 4 hours. The material synthesized were characterized by X-ray powder diffraction, the measurements were carried out in Bruker D8 DaVinci diffractometer, equipped with CuKα radiation , LynxEye linear Position Sensitive Detector, Ni-filter. Data was collect between 8 and 800in 2θ with step size of 0.020and the count time of 0.05 per step. Soller slit 2.50of divergence and 0.2 mm primary slit were used. For the ZnMgAl-HT samples the measurements were performed at different temperatures, range 25-12000C, heating rate 50C/min. It was observed differences among XRD patterns for y greater than 25% of Zn in urea method at 5000C, and for co-precipitation method just for the substitution at 50 and 75% of Zn. These results suggested that the increase in Zn percentage change the structure of calcinated samples.

Design and development of position sensitive detectors for neutron scattering instruments at National Facility for Neutron Beam Research in India

Various neutron scattering instruments at Dhruva reactor, BARC, are equipped with indigenously developed neutron detectors. Range of detectors includes proportional counters, beam monitors and linear position sensitive detectors (PSD). One of the instruments is recently upgraded with multi-PSD system of high efficiency and high resolution PSDs arranged in stacking geometry. These efforts have resulted in improving the throughput of the instrument and reducing experiment time. Global scarcity of 3He has made essential to explore other options like BF3 gas and 10B coatings.PSDs with coaxial geometry using BF3 gas and 10B coating (90% enriched) are fabricated and characterized successfully. These PSDs are used as the alternative to 3He PSD in equivalent geometry. Though efficiency of PSDs in similar dimensions is lower than that with 3He, these large numbers of PSDs can be arranged in multi-PSD system. The PSD design is optimized for reasonable efficiency. An array of 60 BF3 filled PSDs (1 m long) is under development for the Time of Flight Instrument at Dhruva. Further improvement in efficiency can be obtained with novel designs with complex anode-cathode geometry. Various challenges arise for long term operation of PSDs with BF3 gas, in addition to complexity of data acquisition electronics. Study of gas aging with detector fabrication materials has been carried out. PSDs with 10B coating show advantage of non toxic nature but have low efficiency. Multiple 10B layers intercepting neutron beam are used to increase the efficiency. PSD designed with small anode- cathode spacing and array of multiwire grids placed between double sided 10B coated plates are being fabricated. Assembly is arranged in curvilinear geometry with zero parallax. Overview of these developments is presented.

Scanning CCD Detector for X-ray Powder Diffraction

We discuss the design, fabrication and use of a custom CCD detector for x-ray powder diffraction measurements. The detector is mounted on a diffractometer arm, where line-by-line readout of the CCD is coupled to continuous motion of the arm. As the arm moves, the data from the CCD detector are accumulated and can be viewed as if it were a "film strip" with partial powder diffraction rings. Because of the unique design of the camera, both high-resolution and rapid measurements can be performed. Powder diffraction patterns are collected with speeds of a few minutes, or less, with many of the advantages of large area position-sensitive detectors, for example amorphous silicon flat panels, such as high sensitivity, direct evidence of grainy samples and freedom from low-angle asymmetry, but with resolution better than linear position-sensitive detectors and nearly as good as the ultimate in resolution, analyser-crystal detection [2,3].

Development of 3He LPSDs and read-out system for the SANS spectrometer at CPHS

The Compact Pulsed Hadron Source (CPHS) is a 13-MeV proton-linac-driven neutron source under construction in Tsinghua University. Time-of-flight (TOF) small-angle neutron scattering (SANS) spectrometer is one of the first instruments to be built. It is designed to use linear position-sensitive detectors (LPSDs) of 3He gas proportional counters to cover a 1m×1m area. Prototypical LPSDs (Φ=12mm, L=1m) have been made and read-out system is developed based on charge division. This work describes the in-house fabrication of the prototypical LPSDs and design of the read-out system including front-end electronics and data acquisition (DAQ) system. Key factors of the front-end electronics are studied and optimized with PSPICE simulation. DAQ system is designed based on VME bus architecture and FPGA Mezzanine Card (FMC) standard with high flexibility and extendibility. Preliminary experiments are carried out and the results are present and discussed.

Low Noise, High throughput Small-Angle Neutron Scattering of Protein in Solution

Small-Angle Neutron Scattering (SANS) is well-suited to study structure and function of protein in solution by exploiting the natural scattering contrast difference between proteins and other biomolecules such as lipids and nucleic acids. The combination of high neutron flux and low experimental background makes the Bio-SANS instrument at ORNL's High Flux Isotope Reactor (HFIR) an ideal tool to study proteins and other biomolecules within complex biological assemblies and composites, in situ and in-vivo. The procedures used for protein solution scattering at the Bio-SANS are presented here. The scattering signal is collected by a newly-developed Linear Position-Sensitive Detector (LPSD), which has a count rate capability of at least one million neutrons per second. It enables the Bio-SANS to utilize the full potential of the intense cold neutron source at HFIR. The detector-to-sample distance is adjustable from ∼1m to ∼15.3m to provide q-range from 0.0009 1/A to 0.7 1/A. The data collected at different distances are corrected against dark current, pixel efficiency, sample transmission and geometry to produce 1D profiles to be merged into a full scattering data set. A calibrated standard sample or direct beam intensity is used to obtain the absolutely scaled intensity of protein scattering. A few examples are presented here to demonstrate the procedure and the capability. They include scattering from protein crowded by another protein, membrane protein in a membrane-mimic environment, etc.

A prototype of the linear position-sensitive detectors for CPHS

Abstract The time-of-flight (TOF) small-angle neutron scattering (SANS) di_ractometer is one of the first instruments to be built at the Compact Pulsed Hadron Source (CPHS) of Tsinghua University. It requires a 1 × 1 m2 area detector to cover the designed Q-range without moving the detector. We contemplate an array of 1D linear position-sensitive detectors (LPSDs) of 3He gas proportional counters. Each LPSD will have a cylindrical geometry with an active length of 1 m and a diameter of 12 mm. We describe the in-house fabrication of the first LPSDs and the preliminary testing of their performance.

Design and operation of the wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source

The wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source (SNS) is optimized to provide a high neutron flux at the sample position with a large solid angle of detector coverage. The instrument incorporates modern neutron instrumentation, such as an elliptically focused neutron guide, high speed magnetic bearing choppers, and a massive array of (3)He linear position sensitive detectors. Novel features of the spectrometer include the use of a large gate valve between the sample and detector vacuum chambers and the placement of the detectors within the vacuum, both of which provide a window-free final flight path to minimize background scattering while allowing rapid changing of the sample and sample environment equipment. ARCS views the SNS decoupled ambient temperature water moderator, using neutrons with incident energy typically in the range from 15 to 1500 meV. This range, coupled with the large detector coverage, allows a wide variety of studies of excitations in condensed matter, such as lattice dynamics and magnetism, in both powder and single-crystal samples. Comparisons of early results to both analytical and Monte Carlo simulation of the instrument performance demonstrate that the instrument is operating as expected and its neutronic performance is understood. ARCS is currently in the SNS user program and continues to improve its scientific productivity by incorporating new instrumentation to increase the range of science covered and improve its effectiveness in data collection.

SPEAR — ToF neutron reflectometer at the Los Alamos Neutron Science Center

This article discusses the Surface ProfilE Analysis Reflectometer (SPEAR), a vertical scattering geometry time-of-flight reflectometer, at the Los Alamos National Laboratory Lujan Neutron Scattering Center. SPEAR occupies flight path 9 and receives spallation neutrons from a polychromatic, pulsed (20Hz) source that pass through a liquid-hydrogen moderator at 20K coupled with a Be filter to shift their energy spectrum. The spallation neutrons are generated by bombarding a tungsten target with 800MeV protons obtained from an accelerator. The process produces an integrated neutron flux of ∼ 3.4×106 cm−2 s−1 at a proton current of 100μA. SPEAR employs choppers and frame overlap mirrors to obtain a neutron wavelength range of 4.5–16 A. SPEAR uses a single 200mm long 3He linear position-sensitive detector with ∼ 2 mm FWHM resolution for simultaneous studies of both specular and off-specular scattering. SPEAR’s moderated neutrons are collimated into a beam which impinges from above upon a level sample with an average angle of 0.9° to the horizontal, to facilitate air-liquid interface studies. In the vertical direction, the beam converges at the sample position. The neutrons can be further collimated to the desired divergence by finely slitting the beam using a set of two 10B4C slit packages. The instrument is ideally suited to study organic and inorganic thin films with total thicknesses between 5 and 3000 A in a variety of environments. Specifically designed sample chambers available at the instrument provide the opportunity to study biological systems at the solid-liquid interface. SPEAR’s unique experimental capabilities are demonstrated by specific examples in this article. Finally, an outlook for SPEAR and perspectives on future instrumentation are discussed.

Design and performance of vacuum capable detector electronics for linear position sensitive neutron detectors

We describe the design and performance of electronics for linear position sensitive neutron detectors. The eight tube assembly requires 10 W of power and can be controlled via digital communication links. The electronics can be used without modification in vacuum. Using a transimpedance amplifier and gated integration, we achieve a highly linear system with coefficient of determinations of 0.9999 or better. Typical resolution is one percent of tube length.

A neutron reflectometer with horizontal sample geometry at CARR

Abstract A neutron reflectometer with horizontal sample geometry has been developed by the Institute of Chemistry, Chinese Academy of Sciences (ICCAS), and recently installed at China Advanced Research Reactor (CARR) under the participating research team agreement with China Institute of Atomic Energy (CIAE). This instrument is the first neutron reflectometer in China, and is dedicated to the structural characterization of thin films and multilayers of soft matter. For the cold neutron source and curved guide, the feasible wavelength of the incident neutron beam is 4.75 A monochromated by pyrolytic graphite crystals, and this permits the scattering vector Q ranging from –0.23 to 0.4 A−1. This instrument is equipped with a 3He point detector to measure the incident neutron beam and a 3He point detector or linear position sensitive detector to detect the reflected neutron beam. It allows a step-by-step measurement by isochronously changing the incident and reflective angles, and also can be treated as a simple optical imaging element simultaneously measuring neutron reflectivity of multi incident angles using a loosely collimated beam in the absence of significant off-specular scattering. A detailed description of this flexible instrument and its performance characteristics are given.