One-dimensional Detector Research Articles

One-dimensional parallax-free position-sensitive detector for diffraction measurements based on a home-made thin THGEM.

A large parallax-free gas diffraction meter based on a thinner-THGEM (thick gaseous electron multiplier) has been developed at the Beijing Synchrotron Radiation Facility (BSRF). A thinner-THGEM of thickness 200 µm is adopted, which can be shaped into a curve to eliminate parallax-error effects. The detector is designed to have a 48° open angle positioned 20 cm from the powder samples. A front-end electronics board with 128 channels direct-current mode was adapted for the 8 keV BSRF beamline with 0.2 ns/100 ns stable duty cycle. Two powder samples, TiO2 and SnO2, were tested separately. The measured spectra with an angular resolution of 0.148 ± 0.081° are consistent with the data from the powder diffraction file. Combining the gas gain of the thinner-THGEM with the electronic circuit dynamic range, a very broad dynamic range of about 107 could be obtained.

Edge detection methods based on RBF interpolation

Edge detection is a widely used tool in signal/image processing with the aim of identifying abrupt changes or discontinuities in a signal/digital image. For the detection of jump discontinuities in 1D problems, we present an iterative method based on interpolation with Variably Scaled Kernels (VSKs). This is shown to outperform an existing iterative edge detection method based on multiquadric (MQ) radial basis function interpolation. To extend our purely one-dimensional edge detector to any dimension, we then introduce an innovative non iterative technique that detects jumps/edges by identifying the local maxima of the normalized absolute values of the RBF interpolant coefficients. The RBF interpolant is built-upon the compactly supported C 2 Wendland function and exploits its advantageous properties to provide a robust and low-cost method. Numerical examples in 1D and 2D are included to illustrate its effectiveness and efficiency. In the context of edge detection for digital images, comparisons with Canny method are also presented.

High resolution, high efficiency liquid scintillator capillary array for gamma imaging.

We fabricated a liquid scintillator capillary array (LSCA) for gamma imaging with the aim of developing a one-dimensional detector system utilizing a streak camera for high temporal and spatial resolution pulsed gamma radiation detection. The detector's performance was studied in a simulation and via an experiment. The maximum efficiency of the LSCA's emission was at a wavelength of 420 nm. To establish a high fidelity representation of the detector's edge spread function and modulation transfer function (MTF), a slanted edge algorithm was introduced to calculate the edge spread function of the discrete sampling array's image screen. The simulation results showed that the spatial resolution of the LSCA was better for 14 MeV neutrons than for 1.25 MeV gamma radiation. The experimental results show that in comparison with a 6-mm-thick LaBr3 image plate, the LSCA had a higher temporal and spatial resolution when used as a gamma detector. The spatial resolution was 1.1 lp/mm (MTF = 0.1) for the LSCA. In addition, when an ultra-violet streak camera was coupled with the LSCA, it had a comparable sensitivity to that of a 6-mm-thick LaBr3 image plate.

Deconvolution–convolution treatment on powder diffraction data collected with CuKα X-ray and NiKβ filter

A method to remove small CuKβ peaks and step structures caused by NiK-edge absorption as well as CuKα2 sub-peaks from powder diffraction intensity data measured with Cu-target X-ray source and Ni-foil filter is proposed. The method is based on deconvolution–convolution treatment applying scale transform of abscissa, Fourier transform, and a realistic spectroscopic model for the source X-ray. The validity of the method has been tested by analysis of the powder diffraction data of a standard LaB6 powder (NIST SRM660a) sample, collected with the combination of CuKα X-ray source, Ni-foil Kβ filter, flat powder specimen and one-dimensional Si strip detector. The diffraction intensity data treated with the method have certainly shown background intensity profile without CuKβ peaks and NiK-edge step structures.

Improvement of deconvolution–convolution treatment of axial-divergence aberration in Bragg–Brentano geometry

An improved method to correct observed shift and asymmetric deformation of diffraction peak profile caused by the axial-divergence aberration in Bragg–Brentano geometry is proposed. The method is based on deconvolution–convolution treatment applying scale transform of abscissa, Fourier transform, and cumulant analysis of an analytical model for the axial-divergence aberration. The method has been applied to the powder diffraction data of a standard LaB6 powder (NIST SRM660a) sample, collected with a one-dimensional Si strip detector. The locations, widths and shape of the peaks in the deconvolved–convolved powder diffraction data have been analyzed. The finally obtained whole powder diffraction pattern ranging from 10° to 145° in diffraction angle has been simulated by the Pawley method applying a symmetric Pearson VII peak profile model to each peak with ten background, two peak-shift, three line-width, and two peak-shape parameters, and the Rp value of the best fit has been estimated at 4.4%.

Accurate Online Measurement of Iron Concentration in Galvannealed Coating Layers by Shift of X-ray Diffraction Peak

The authors have developed a new online measurement system for the Fe concentration in galvannealed (GA) coating layers based on the proportionality between the X-ray diffraction (XRD) peak angle of the δ1 phase and the Fe concentration. The online system was realized by high speed measurement of the XRD peak angle by a one-dimensional detector and use of a correction algorithm for the angular error caused by the displacement of the GA strip surface from the measurement position. The XRD profile and displacement were simultaneously measured by the one-dimensional detector and a laser displacement meter, respectively. The high accuracy of this new online system was demonstrated in a continuous galvanizing line with GA steel strips of Si-added and Si-free base steels. The developed system showed sufficiently high accuracy even with the Si-added base steel, with which adequate accuracy could not be obtained with conventional online systems, based on the diffracted intensity of the Γ phase, due to the suppression of Γ phase formation. Since the δ1 phase is the major phase of the GA layers, the main advantage of the developed system is that its accuracy is less sensitive to the composition of the base steel. The developed system can be applied to other online measurement applications in the steel industry for various purposes such as measurement of phase transition, orientation, crystallinity, strain and other features.

Effective Atomic Number Measurement with Energy-Resolved Computed Tomography Using Two-Dimensional “transXend” Detector

Introduction: We have previously developed an effective atomic number (Zeff) measurement method using linear attenuation coefficients (LACs) obtained by energy-resolved computed tomography (CT) with one-dimensional (1D) detector. The energy-resolved CT was performed with a “transXend” detector, which measured X-rays as electric current and then gave X-ray energy distribution with unfolding analysis using pre-estimated response function (RF). The purpose of this study is to measure Zeff by the energy-resolved CT using a flat panel detector (FPD). Methods: To demonstrate a 2D transXend detector, we developed the stripe absorbers for the FPD. Eleven human tissue-equivalent material rods which were grouped into four material categories were measured by X-rays with 120 kVp tube voltage, 2.3 mA tube current, and 1.0 s exposure time. Zeff is measured by the ratio of LACs with two different pseudo-monochromatic X-ray energies. RFs of each rod material were estimated by numerical calculation. First, we employed the RF estimated for the same rod material (self-RF scenario). Second, we employed the RF estimated for the different rod materials in the same material category (cross-RF scenario). The purpose of the cross-RF scenario was to find representative rod materials in each material category. Results: Upon the self-RF scenario, measured Zeffs were systematically underestimated. Median relative error to theoretical Zeff was -6.92% (range: -7.89% - -4.60%). After normalizing measured Zeffs to the theoretical one for Breast, median relative error improved to -0.75% (range: -1.79% - +1.73%). Upon the cross-RF scenario, the representative rod materials were found in two material categories. Conclusion: Zeff measurements were performed by energy-resolved CT using 2D transXend detector with numerically-estimated RF data. Normalized Zeffs for all rod materials in the self-RF scenario were in good agreement with the theoretical ones.

Development of One-Dimensional Norm Detector for Nanosecond-Level Transient Electric Field Measurement

This paper develops a one-dimensional norm detector for nanosecond-level transient electric field (E-field) measurement based on the digital measurement technology. It has two main advantages over the traditional measurement method. First, the measured signals can be stored and no transmission line is needed. Hence, it can detect the E-field coupled in hermetically sealed cavities, such as the cockpit of an aircraft or a vehicle under electromagnetic compatibility test. Second, commonly used norms of the measured waveform can be acquired by the signal processing software quickly and conveniently. Therefore, the efficiency of the measurement experiment can be improved. This paper describes the detailed realization of the norm detector and the design of its signal processing software. The maximum sampling rate of the norms detector is 2 GSPS and the memory depth is 8 kB. Via adjusting the height of the antenna, the measuring range can be 0.1–55 kV/m and the estimated operation bandwidth is 1 kHz–460 MHz. The norm detector is tested and compared with the traditional E-field sensor with the fiber-optic link by measuring the square waveform and the actual electromagnetic pulse waveform. Furthermore, the norm detector can measure magnetic field, coupled current or high-voltage pulse by a simple structural modification.

A two-dimensional partial response maximum likelihood detection scheme for misalignment compensation in holographic data storage systems

A two-dimensional (2D) partial response maximum likelihood (PRML) detection scheme for misalignment compensation for holographic data storage systems is proposed. In the proposed detection scheme, a misalignment estimator and a predetermined table are added to the conventional 2D PRML scheme to estimate and reflect the effect of misalignment in the vertical and horizontal directions, respectively. In the vertical detection, the misalignment estimator located behind the vertical 2D equalizer and one-dimensional PRML detector estimates the misalignment by the adaptive least-mean-square algorithm (LMS). To improve the estimation accuracy, the misalignment is estimated iteratively by modifying the vertical equalizer coefficients reflecting the estimated misalignment. By considering the estimated misalignment, the vertical 2D equalizer coefficients, horizontal 2D equalizer coefficients, and 2D partial response (PR) target are selected among the predetermined table. In the predetermined table, the vertical and horizontal 2D equalizer coefficients for various misalignments were previously computed on the basis of the misalignment and 2D PR target by the LMS. By employing the horizontal 2D equalizer coefficients and 2D PR target reflecting the misalignment in the horizontal detection, the effect of misalignment is effectively mitigated. Simulation results show that the proposed scheme has more than 3 dB gains than the conventional scheme in the 10% misalignment in the horizontal and vertical directions.

Calibration of large area Micromegas detectors using cosmic rays

Currently m2-sized micropattern detectors with spatial resolution better than 100 μm and online trigger capability are of big interest for many experiments. Large size in combination with superb spatial resolution and trigger capability implicates that the construction of these detectors is highly sophisticated and imposes strict mechanical tolerances. We developed a method to survey assembled and working detectors on potential deviations of the micro pattern readout structures from design value as well as deformations of the whole detector, using cosmic muons in a tracking facility. The LMU Cosmic Ray Facility consists of two 8 m2 ATLAS Monitored Drift Tube chambers (MDT) for precision muon reference tracking and two segmented trigger hodoscopes with sub-ns time-resolution and additional 10 cm position information along the wires of the MDTs. It provides information on homogeneity in efficiency and pulse height of one or several micropattern detectors installed in between the MDTs. With an angular acceptance of −30° to +30° the comparison of the reference muon tracking with centroidal position determination or time projection chamber like track reconstruction in the micropattern detector allows for calibration in three dimensions. We present results of a m2-sized one-dimensional resistive strip Micromegas detector consisting of two readout boards with in total 2048 strips, read out by 16 APV25 front-end boards. This 16-fold segmentation along the precision direction in combination with a 10-fold segmentation in orthogonal direction by the resolution of the trigger hodoscope, allows for very detailed analysis of the 1 m2 detector under study by subdivision into 160 partitions, each being analyzed separately. We are able to disentangle deviations from the readout strip straightness and global deformation due to the small overpressure caused by the Ar:CO2 (93:7) gas mixture flux. We introduce the alignment and calibration procedure, report on homogeneity in efficiency and pulse height and present results on deformation and performance of the m2-sized Micromegas.

DxTools: processing large data files recorded with the Bruker D8 diffractometer

Data processing is the daily reality for crystallographers, who often seek to automate this repetitive task. With modern commercial diffractometers allowing for more elaborate experiments to be performed, the use of commercial software is almost unavoidable for processing data, because these are often provided in a manufacturer-specific format. This is especially the case when the intensity is recorded as a function of more than one single scanning motor and/or when recording data with a one-dimensional detector. A simple, free and open-source alternative is here presented to process the type of diffraction data recorded with the Bruker D8 diffractometer. It allows handling of data files (in uxd and brml format) corresponding to reciprocal space maps (in the Qx Qz and Qx Qy planes), temperature-dependent scans, spatial scans, sin2ψ measurements and pole figures. The program is easy to use and can be extended to any file format. It can be downloaded from https://aboulle.github.io/DxTools/.

FPGA-based GEM detector signal acquisition for SXR spectroscopy system

The presented work is related to the Gas Electron Multiplier (GEM) detector soft X-ray spectroscopy system for tokamak applications. The used GEM detector has one-dimensional, 128 channel readout structure. The channels are connected to the radiation-hard electronics with configurable analog stage and fast ADCs, supporting speeds of 125 MSPS for each channel. The digitalized data is sent directly to the FPGAs using fast serial links. The preprocessing algorithms are implemented in the FPGAs, with the data buffering made in the on-board 2Gb DDR3 memory chips. After the algorithmic stage, the data is sent to the Intel Xeon-based PC for further postprocessing using PCI-Express link Gen 2. For connection of multiple FPGAs, PCI-Express switch 8-to-1 was designed. The whole system can support up to 2048 analog channels. The scope of the work is an FPGA-based implementation of the recorder of the raw signal from GEM detector. Since the system will work in a very challenging environment (neutron radiation, intense electro-magnetic fields), the registered signals from the GEM detector can be corrupted. In the case of the very intense hot plasma radiation (e.g. laser generated plasma), the registered signals can overlap. Therefore, it is valuable to register the raw signals from the GEM detector with high number of events during soft X-ray radiation. The signal analysis will have the direct impact on the implementation of photon energy computation algorithms. As the result, the system will produce energy spectra and topological distribution of soft X-ray radiation. The advanced software was developed in order to perform complex system startup and monitoring of hardware units. Using the array of two one-dimensional GEM detectors it will be possible to perform tomographic reconstruction of plasma impurities radiation in the SXR region.

Proton computed tomography using a 1D silicon diode array.

Proton radiography (PR) and proton computed tomography (PCT) can be used to measure proton stopping power directly. However, practical and cost effective proton imaging detectors are not widely available. In this study, the authors investigated the feasibility of proton imaging using a silicon diode array. A one-dimensional silicon diode detector array (1DSDA) was aligned with the central axis (CAX) of the proton beam. Polymethyl methacrylate (PMMA) slabs were used to find the correspondence between the water equivalent thickness (WET) and 1DSDA channel number. Two-dimensional proton radiographs were obtained by translation and rotation of a phantom relative to CAX while the proton nozzle and 1DSDA were kept stationary. A PCT image of one slice of the phantom was reconstructed using filtered backprojection. PR and PCT images of the PMMA cube were successfully acquired using the 1DSDA. The WET of the phantom was measured using PR data. The resolution and maximum error in WET measurement are 2.0 and 1.5 mm, respectively. Structures down to 2.0 mm in size could be resolved completely. Reconstruction of a PCT image showed very good agreement with simulation. Limitations in spatial resolution are attributed to limited spatial sampling, beam collimation, and proton scatter. The results demonstrate the feasibility of using silicon diode arrays for proton imaging. Such a device can potentially offer fast image acquisition and high spatial and energy resolution for PR and PCT.

Turbulence burst over four micro-topographies in the wind tunnel

Investigating the mechanisms of wind-sand movement is essential to deeply understand sand storm and desertification process, and further to control the wind-sand hazards. It is considered that turbulence burst may have great influence on the motion of sand particles. But current theoretical and experimental studies mostly concentrate on the turbulence burst over flat surface or in the water. Sand dunes and sand ripples are basic forms of desert landscape, and the slope gradient will inevitably affect the frequency of turbulence burst. In this paper, instantaneous velocities over 4 different sand surfaces, including smooth flat bed, flat sand bed, sand bed with ripples and slope bed, are measured using one-dimensional hot wire detector. The results show that for the slope sand surface, wind field in leeward slope region is a buffering zone, which doesn't obey logarithmic function. On the flat sand surface, the distribution of turbulence intensity and Reynolds normal stress are gradually decreasing along the height of boundary layer. On the slope sand surface, the stronger turbulence behavior happens near the top of slope. Based on Mu-level method analysis, it is found that the turbulence bursts on both flat sand surface and sand ripples mainly occur near the surface, and gradually decrease with the height. Compared to flat sand surface, the burst frequency is 30%~50% higher on the sand ripples surface, which indicates that micro-topography have an influence on the turbulence burst. This work may be helpful in understanding the initiation and transportation of sand storm, as well as the desertification process.

Multi-tube area detector developed for reactor small-angle neutron scattering spectrometer SANS-J-II

A newly developed multi-tube area detector for a small-angle neutron scattering (SANS) spectrometer (SANS-J-II) at the research reactor JRR-3 in Tokai, Japan, has been implementedviathe use of one-dimensional position-sensitive3He detectors (tubes). Ninety-six active tubes of 8 mm in diameter and 650 and 580 mm in length were filled with 15 atm (1.52 MPa) of3He and aligned vertically parallel in order to cover a sufficiently large area for small-angle scattering measurement. These tubes are enclosed in an air chamber together with neutron encode and GATENET modules (VME boards), which compose a standard data acquisition system for the spallation neutron source of the Japan Proton Accelerator Research Complex. This system facilitates the acquisition of time-of-flight neutron event data. The multi-tube detector is mounted on a truck moving in a vacuum chamber of the SANS spectrometer. After discriminating noise originating from γ-rays, and calibrating the positions and sensitivities of individual tubes, the resolution was determined (i.e.channel widths along parallel and vertical directions along a tube). The counting rate of one tube was determined to be 1.4 × 103counts per second with a counting loss of 1%. This implies that the new detector, composed of 96 tubes, can detect more than 105neutrons per second with a counting loss of 1%. To demonstrate its use, small-angle scattering originating from a diblock copolymer film with a highly oriented lamellar microdomain was observed. The data acquisition in event mode has a great advantage in time-resolved measurements that are synchronized with external stimuli imposed on a sample.

SUPR: Spectral Unmixinig Plate Reader for Live-Cell FRET Biosensor Drug Screening

We have developed a high-throughput Spectral Unmixing Plate Reader (SUPR) which can acquire a fluorescence emission spectrum across 384 wells, with short (< 4 min) read time for the entire plate. The entire spectrum is recorded at once with a compact spectrometer equipped with an uncooled one-dimensional array detector. For application to FRET in living cells, FRET protein biosensors, with genetically encoded GFP (donor) and RFP (acceptor) tags, are expressed in HEK cells, and single-component spectra are acquired from water (Raman), untransfected cells (autofluorescence), cells expressing donor only, and cells expressing acceptor only. Each observed spectrum is decomposed into a linear combination of component spectra to determine FRET efficiency. The method enables unprecedented speed, precision, and accuracy. It rigorously and painlessly accounts for phenomena such as bleed-through of the donor emission into the acceptor channel, cross-talk associated with direct excitation of the acceptor, and cell autofluorescence. Excitation and detection are both from the top, so low-cost polypropylene plates typically used in qPCR work very well in this application. This novel technology has been combined with our previously developed fluorescence lifetime technology (Petersen et al, Rev Sci Inst, 2014) allowing for high-throughput quantitation of FRET efficiency from independent measurements. We have screened small-molecule libraries with an intramolecular cardiac calcium pump FRET biosensor, expressed in living cells (Gruber et al., J. Biomol Screening, 2014) using this multiplexed fluorescence detection platform and identified several previously unknown small-molecule effectors. The information obtained from both fluorescence lifetime and spectrum measurements reduced the number of false-positives and increased confidence in our hit selection methods. The development of this technology and screening assay will prove useful for drug discovery but also answering basic biological questions with fluorescence based assays.

Note: An X-ray powder diffractometer with a wide scattering-angle range of 72° using asymmetrically positioned one-dimensional detectors.

An X-ray powder diffractometer has been developed for a time-resolved measurement without the requirement of a scattering angle (2θ) scan. Six one-dimensional detector modules are asymmetrically arranged in a vertical line at a designed distance of 286.5 mm. A detector module actually covers a diffraction angle of about 12° with an angular resolution of 0.01°. A diffracted intensity pattern is simultaneously recorded in a 2θ angular range from 1.63° to 74.37° in a "one shot" measurement. We tested the performance of the diffractometer with reference CeO2 powders and demonstrated diffraction measurements from an operating lithium-air battery.

Simple and accurate optical height sensor for wafer inspection systems

An accurate method for measuring the wafer surface height is required for wafer inspection systems to adjust the focus of inspection optics quickly and precisely. A method for projecting a laser spot onto the wafer surface obliquely and for detecting its image displacement using a one-dimensional position-sensitive detector is known, and a variety of methods have been proposed for improving the accuracy by compensating the measurement error due to the surface patterns. We have developed a simple and accurate method in which an image of a reticle with eight slits is projected on the wafer surface and its reflected image is detected using an image sensor. The surface height is calculated by averaging the coordinates of the images of the slits in both the two directions in the captured image. Pattern-related measurement error was reduced by applying the coordinates averaging to the multiple-slit-projection method. Accuracy of better than 0.35 μm was achieved for a patterned wafer at the reference height and ±0.1 mm from the reference height in a simple configuration.

The benefits of one-dimensional detectors for high-pressure powder X-ray diffraction

High-pressure powder X-ray diffraction is a fundamental technique for investigating structural responses to externally applied force. Synchrotron sources and two-dimensional detectors are required. In contrast to this conventional setup, high-resolution beamlines equipped with one-dimensional detectors could offer much better resolved peaks but cannot deliver accurate structure factors because they only sample a small portion of the Debye rings, which are usually inhomogeneous and spotty because of the small amount of sample. In this study, a simple method to overcome this problem is presented and successfully applied to solving the structure of an L-serine polymorph from powder data. A comparison of the obtained high-resolution high-pressure data with conventional data shows that this technique, providing up to ten times better angular resolution, can be of advantage for indexing, for lattice parameter refinement, and even for structure refinement and solution in special cases.

MYTHEN2 detector series

We would like to inform users that the MYTHEN 1K detector is announced for end-ofsales as of 31 December 2015. During the past decade, MYTHEN 1K detectors have transformed the field of X-ray powder diffraction (XRPD), increasing the accuracy of XRPD data, boosting timeresolved measurements and introducing pair distribution function analysis to laboratory diffractometers. This fruitful life cycle would not have been possible without the creative diffraction and scattering community, who exploited every feature of Hybrid Photon Counting (HPC) technology. DECTRIS thanks numerous users, original equipment manufacturers and synchrotron partners for valuable collaborations and inspiration for future developments. The end-of-life of MYTHEN 1K does not mean the end-of-support. Spare parts and software support will be available for a period of five years. For our synchrotron partners, MYTHEN 1K will be offered for construction and upgrades of large detector systems, comprising more than four modules, like MYTHEN 6K and MYTHEN 24K. DECTRIS’ one-dimensional detector line will be continued with MYTHEN2. The two series, X for synchrotron and R for laboratory and industrial use (Fig. 1), preserve all the benefits of the MYTHEN technology and respond to our customers’ requirements: compact modules with 1280 and 640 strips, noise-free single photon counting down to 4 keV and system modularity with DCS4. The MYTHEN2 X series offers frame rates up to 1 kHz for optimal temporal resolution and throughput at synchrotron facilities, while the price–performance ratio and compact housing of the R series is suitable for any laboratory diffractometer. MYTHEN2 will continue to provide professional solutions for classical and inventive experimental setups. ISSN 1600-5767