Area Position Sensitive Detector Research Articles

HRTex: a high-resolution texture data processing tool for monochromatic neutron diffraction based on the pixel projection method

HRTex is a new texture data processing tool for two-dimensional position-sensitive area detectors on monochromatic neutron diffractometers. With the aim of improving the resolution and accuracy of pole figure calculations, HRTex treats the raw data of the area detector for each pixel and projects the intensity of each pixel directly onto a high-resolution pole figure. With the resultant refinement of the resolution, HRTex can distinguish close texture peaks with a flexible resolution setting and reduced information loss. Test results of HRTex on the data sets of two samples measured by two different neutron facilities are analysed, and the improvements in accuracy, resolution and efficiency of the pole figure calculation are discussed.

Experimental study of a boron coated straw detector module at CPHS

Large-area position-sensitive thermal neutron detector plays an important role in the small angle neutron scattering (SANS) technique. Considering the shortage of 3He supply, a detector module composed of 64 boron coated straw (BCS) tubes was developed in the present work for the time-of-flight (TOF) SANS instrument that will be deployed on the Compact Pulsed Hadron Source (CPHS) at Tsinghua University. In this paper, 64 straw tubes were tightly packed into 8 rows by 8 columns. A multiplex readout system was utilized to locate the straw tube that has registered a neutron deposition event in the detector module, and to reconstruct the longitudinal position according to the charge division method. Several key aspects, including the pulse height spectrum, the spatial resolution and the position linearity, have been studied using the CPHS neutron beams generated by 3 MeV protons. The results indicated that the detector module can achieve an average axial spatial resolution of 5.8± 0.2 mm with a good position linearity. The neutron detection efficiency of the detector module was simulated with Geant4 code and was found to be larger than 39% for the neutrons at CPHS operated with 13 MeV proton beams in the future. It was concluded that the BCS tubes can be used to build the two-dimensional position-sensitive area detector for the TOF-SANS instrument at CPHS.

Depth-Resolved X-ray Absorption Spectroscopy by Means of Grazing Emission X-ray Fluorescence.

Grazing emission X-ray fluorescence (GEXRF) is well suited for nondestructive elemental-sensitive depth-profiling measurements on samples with nanometer-sized features. By varying the grazing emission angle under which the X-ray fluorescence signal is detected, the probed depth range can be tuned from a few to several hundred nanometers. The dependence of the XRF intensity on the grazing emission angle can be assessed in a sequence of measurements or in a scanning-free approach using a position-sensitive area detector. Hereafter, we will show that the combination of scanning-free GEXRF and fluorescence detected X-ray absorption spectroscopy (XAS) allows for depth-resolved chemical speciation measurements with nanometer-scale accuracy. While the conventional grazing emission geometry is advantageous to minimize self-absorption effects, the use of a scanning-free setup makes the sequential scanning of the grazing emission angles obsolete and paves the way toward time-resolved depth-sensitive XAS measurements. The presented experimental approach was applied to study the surface oxidation of an Fe layer on the top of bulk Si and of a Ge bulk sample. Thanks to the penetrating properties and the insensitivity toward the electric conduction properties of the incident and emitted X-rays, the presented experimental approach is well suited for in situ sample surface studies in the nanometer regime.

Scanning-free grazing emission x-ray fluorescence by means of an angular dispersive arrangement with a two-dimensional position-sensitive area detector

We report on the application of a two-dimensional position-sensitive area detector towards grazing emission x-ray fluorescence (GEXRF) spectroscopy. GEXRF allows for surface-sensitive studies with nanometer-scale accuracy in the depth direction by measuring the intensity variation of an x-ray fluorescence line with the grazing emission angle. The presented experimental setup is based on a fixed sample-detector arrangement and does not require any moving components. We show that the dispersion of the grazing emission angle along a position-sensitive detector allows to acquire with an excellent angular resolution a full GEXRF profile in a single measurement. Moreover, the use of a two-dimensional detector allows to perform experiments with an increased solid angle of detection per emission angle. This results in combination with the nonsequential and simultaneous acquisition of the GEXRF profiles of different emission lines in considerably reduced acquisition times. The realization, the demands, and the main characteristics of the scanning-free GEXRF setup will be presented. A few experimental examples will serve to illustrate the analytical possibilities offered by the presented setup.

The Application of PSD in Vibration Measurment

Position Sensitive Detector (PSD) is a new type of photoelectric position sensor. Compared with traditional CCD, PSD has high position resolution, simple circuit and fast response. Operational principle of PSD and how it can be used in vibration system are firstly shown in this paper. Based on the MCU, a vibration measurement system using a BOS-PSD0220 type sensor is designed. The system is then experimentally measured at the most sensitive area of PSD. The result is compared with data calculated by MATLABLE, which demonstrates PSD is a good choice for vibration measurement.

Synchrotron measurement of the 3D shape of X-ray reflections from the γ/γ′-microstructure of nickel-base superalloys

Abstract The 3D shape of X-ray reflections from the γ/γ′-microstructure of a nickel-base superalloy was investigated using synchrotron X-ray radiation and a position sensitive area detector. The measurements were performed on the 4th generation single-crystal nickel-base superalloy TMS138. The results show that X-ray reflections from non-cubic crystallographic planes have a complex 3D shape which changes during rafting. The 3D intensity distributions contain information about the spacing of the planes and their orientation as well. Whereas h00 reflections show the usual splitting into a γ′ and one γ-subreflection, the hh0 and hhh reflections show two and three γ-peaks respectively, resulting from the different types of {100} matrix channels. Therefore, these 3D diffraction measurements supply additional information about the spatial distribution of microstrains.

A new position sensitive area detector for high-speed and high-sensitivity X-ray diffraction analysis

A state-of-art semiconductor technology-based position sensitive area detector, namely D/teX-25, has recently been developed for high-speed and high-sensitivity X-ray diffraction (XRD) analysis of materials. X-ray powder diffraction intensities obtained by a D/teX-25 detector were found to over 50 times higher than those by a conventional scintillation counter. A D/teX-25 detector mounted on a conventional 2 kW XRD system has been used to collect ultrafast XRD data with scanning speeds up to 160°2θ per minute. Ultrahigh-speed XRD is particularly useful for time-resolved dynamical and in-situ studies. A D/teX-25 detector was successfully used on a Rigaku XRD differential scanning calorimetry (DSC) system for simultaneous measurements of XRD and DSC data under controlled temperature and humidity conditions. This has made possible the study of complex and rapid phase transformations of pharmaceutical terfenadine. The D/teX-25 area detector has also been used for recording two-dimensional XRD patterns showing the particle-size effects on α-quartz powder intensities and to obtain digital X-ray topographic images of a complex dislocation network in a Si wafer.

A data-acquisition system for area detectors

The use of position-sensitive area detectors with high-flux radiation sources demands high-rate data-acquisition systems. Ideally, such devices should be commercially available and machine independent. In this paper, the basic features of such a system are described. The steps are highlighted that determine the counting rates of present-day addressing-logic and computer-bus speeds. The improvements expected with a new industrial standard bus system are briefly described.

A small-distortion two-dimensional position-sensitive detector (PSD) with on-chip MOSFET switches

A new type of two-dimensional (2D) position-sensitive detector (PSD) for precise light beam position sensing is reported. Four wide MOSFET gates are added around the square sensing area of a conventional tetralateral 2D PSD. This changes the tetralateral 2D PSD to a one-dimensional (1D) PSD, but its sensing direction can be alternated between the horizontal and vertical directions. This results in as good a linearity of position sensing in the 2D PSD as in the 1D PSD. Experimental results show the position non-linearity of the output signal to be drastically reduced from 7% in the conventional operation to 0.02% in the MOSFET switching operation. The maximum operating frequency of the MOSFETs is about 5 kHz for this prototype device.

Synchrotron radiation applications of charge coupled device detectors (invited)

Scientific charge coupled devices (CCDs) offer many opportunities for high brightness synchrotron radiation applications where good spatial resolution and fast data acquisition are important. We describe the use of virtual-phase CCD pixel arrays as two-dimensional area detectors illustrating the techniques with results from recent x-ray scattering, imaging, and absorption spectroscopy studies at NSLS, CHESS, SRC, and LURE DCI. The virtual phase architecture allows direct frontside illumination of the CCD detector chips giving advantages in the speed and sensitivity of the detector. Combining developments in x-ray optics (dispersive geometry), position sensitive area detectors (CCDs), and fast data acquisition, we have been able to perform time-resolved measurements at the microsecond level. Current developments include faster data transfer rates so that the single bunch timing structure of third generation synchrotron sources can be exploited.

Time-of-Flight Pulsed Neutron Diffraction Study on Uniaxial Stress-Induced Domain Switching in LaNbO4

The domain orientation switching phenomena in the ferroelastlc material LaNbO4 were observed by means of a time-of-flight neutron diffraction technique using a position-sensitive area detector. When stress is applied to the direction nearly perpendicular to (100) of one of the domains in the specimen, the a- and c-axes are easily transformed into the c- and a-axes of another domain, respectively. The domains with [001] nearly parallel to the stress direction do not switch orientation. Thus, the domain which occupied 34% of the specimen at the initial stage expanded up to 92% of the total volume by switching from other orientated domains. The estimated stress was 600 gW/mm2 at the final stage. The mechanism of switching orientation can structurally be interpreted by a small rotation and a small displacement of NbO4 tetrahedra at the domain boundary which is a transient zone with a prototype structure.

A time resolving data acquisition system for multiple high-resolution position sensitive detectors

An advanced time-resolving data collection system for use in neutron and X-ray spectrometry has been implemented and put into routine operation. The system collects data from high-resolution position-sensitive area detectors with a maximum cumulative rate of 10/sup 6/ events per second. The events are sorted, in real-time, into many time-slice arrays. A programmable timing control unit allows for a wide choice of time sequences and time-slice array sizes. The shortest dwell time on a slice can be below 1 ms, and the delay to switch between slices is zero.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Hydrogen-deuterium exchange in structural biology

Abstract The large difference in neutron scattering length of hydrogen and deuterium atoms provides a unique tool to study biological macromolecules. These molecules exist in an aqueous environment and have an atomic composition of about 50% hydrogen atoms with the rest being mainly carbon, oxygen and nitrogen. By simply changing the ratio of hydrogen to deuterium the contrast of a sample constituent can be changed without altering the chemical composition. The scattering difference between the hydrogen isotopes has now been used to study structural details of proteins, viruses, nucleic acid protein complexes and membranes. The use of small-angle scattering analysis from proteins in solution is a particularly good example of the power of this new technique. From the first experiments with myoglobin, hemoglobin and TMV solutions in 1968 at the HFBR in Brookhaven it became, however, soon evident that the flux was low and the detection system of a conventional spectrometer was inadequate to measure precisely small differences in the scattering pattern. Since these solution scattering patterns are circularly symmetrical, a development of multidetector systems was the first step to alleviate the need for better data. From an early five detector system [1] the development of linear and two-dimensional position sensitive detectors continues to this day [2–6]. Today, position sensitive area-detectors with an efficiency of 80% and 1.3 mm resolution with an active area of 50 cm × 50 cms are available. These detectors have a counting rate capability of 2 × 10 5 neutrons/s. Other instrumentation developments to facilitate the study of biomolecules include (1) cold moderators, (2) thin film multilayer monochromators [7–9], (3) neutron guides made either of multilayer supermirrors or coated with 58 Ni [10,11], (4) various crystal and mirror focusing devices [12,13]. Some of these features have been incorporated in a small-angle neutron spectrometer at the High Flux Beam Reactor at the Brookhaven National Laboratory. This spectrometer has a unique combination of features such as a high resolution area-detector, adjustable wavelength bandwidth and automated sample changer.

Discrimination Between Neutrons and Gamma Rays and Evaluation of Dose with a Position Sensitive Semiconductor Detector in a Mixed Field

Abstract The application of a surface barrier position sensitive detector (PSD) for discrimination between neutrons and gamma rays in a mixed field is investigated. A centre part of the sensitive area of PSD is covered with the n-p converter foil and the energy and position signals from the single detector are used for identification of neutrons and gamma rays. Output signals are fed to multichannel analysers and a computer, and dose rates are evaluated separately for neutrons and gamma rays, taking account of energy spectra and reaction efficiencies, by an unfolding calculation in real time.

Improvement of the quality of the data collected using a position-sensitive detector

A procedure for integrating the intensities of diffraction peaks which optimizes the signal-to-noise ratios and minimizes the possibility of introducing systematic errors has been extended to the data collected using a position-sensitive area detector. This technique, called “dynamic mask procedure”, is capable of finding precise boundaries of the peaks on the basis of the variances in the signal. It can now be applied to X-ray and neutron data collected on films and using one- and two-dimensional position-sensitive detectors. A test using the neutron data collected with an area detector showed a significant decrease in the estimated standard deviations of the integrated peak intensities compared with the traditional techniques of peak summation.

Neutron scattering studies of biological macromolecules in solution

Small-angle neutron scattering studies of biological macromolecules have developed rapidly in recent years due to the advent of high neutron-flux reactors,† efficient position-sensitive area detectors for neutrons (Allemand et al. 1975) and novel design of instruments (Ibel, 1976). At the same time position-sensitive detectors for X-rays (Gabriel &amp; Dupont, 1972) have revitalized the small-angle X-ray scattering field (Kratky &amp; Pilz, 1972; Luzzati et al. 1976) and it is now becoming clear that neutrons and X-rays can provide complementary structural information on biological complexes.