High-resolution Position-sensitive Detector Research Articles

A ∼100 μm-resolution position-sensitive detector for slow positronium

In this work we describe a high-resolution position-sensitive detector for positronium. The detection scheme is based on the photoionization of positronium in a magnetic field and the imaging of the freed positrons with a Microchannel Plate assembly. A spatial resolution of (88±5) μm on the position of the ionized positronium –in the plane perpendicular to a 1.0 T magnetic field– is obtained. The possibility to apply the detection scheme for monitoring the emission into vacuum of positronium from positron/positronium converters, imaging positronium excited to a selected state and characterizing its spatial distribution is discussed. Ways to further improve the spatial resolution of the method are presented.

Installation of a high-resolution position-sensitive scintillation detector in the small and wide angle neutron scattering instrument (TAIKAN), MLF, J-PARC

The small and wide angle neutron scattering instrument (TAIKAN) installed at the Material and Life Science Experimental Facility (MLF), Japan Proton Accelerator Research Complex (J-PARC) can cover a Q-range from 5 × 10−3 to 17 Å−1 simultaneously, where the magnitude of the scattering vector Q is defined by Q = 4πsin(θ/2)/λ (θ and λ represent the scattering angle and the wavelength, respectively). To extend the accessible low Q-limit (Qmin) to a value in the order of 10−4 Å−1, we successfully installed an ultra-small-angle detector with a spatial resolution of approximately 0.41 mm × 0.41 mm in TAIKAN. This detector is a high-resolution position-sensitive detector (HR-PSD), comprising a cross-wired position-sensitive photomultiplier tube and a ZnS/6LiF scintillator. HR-PSDs of the same type have been installed on steady-state small-angle neutron scattering (SANS) instruments at the research reactor (JRR-3), Japan. Comparing with these previously installed the HR-PSDs, we improved most of the HR-PSD components such as the scintillator, preamplifier, and data acquisition systems to increase its maximum count rate. A maximum count rate of 46 kcps was achieved with 10% counting loss, which is 2.3 times for those installed in the steady-state SANS instruments at JRR-3. Using the ultra-small-angle detector with existing 3He detector banks, TAIKAN can simultaneously cover a Q-range from 8 × 10−4 Å−1 to 17 Å−1 (over four orders of magnitude in Q).

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.

Performance of high-resolution position-sensitive detectors developed for storage-ring decay experiments

As next generation spectroscopic tools, heavy-ion cooler storage rings will be a unique application of highly charged RI beam experiments. Decay spectroscopy of highly charged rare isotopes provides us important information relevant to the stellar conditions, such as for the s- and r-process nucleosynthesis. In-ring decay products of highly charged RI will be momentum-analyzed and reach a position-sensitive detector set-up located outside of the storage orbit. To realize such in-ring decay experiments, we have developed and tested two types of high-resolution position-sensitive detectors: silicon strips and scintillating fibers. The beam test experiments resulted in excellent position resolutions for both detectors, which will be available for future storage-ring experiments.

Modeling of ion beam induced charge sharing experiments for the design of high resolution position sensitive detectors

In a multi-electrode device, the motion of free charge carriers generated by ionizing radiation induces currents on all the electrodes surrounding the active region [1]. The amount of charge induced in each sensitive electrode is a function of the device geometry, the transport parameters and the generation profile. Hence this charge sharing effect allows the signal from each sensitive electrode to provide information about the electrical characteristics of the device, as well as information on the location and the profile of each ionization track.The effectiveness of such approach was recently demonstrated in Ion Beam Induced Charge (IBIC) experiments carried out using a 2MeV He microbeam scanning over a sub-100μm scale silicon device, where the ion strike location point was evaluated through a comparative analysis of the charge induced in two independent surface electrodes coupled to independent data acquisition systems [2].In this report, we show that the Monte Carlo method [3] can be efficiently exploited to simulate this IBIC experiment and to model the experimental data, shedding light on the role played by carrier diffusion, electronic noise and ion beam spot size on the induction of charge in the sensitive electrodes. Moreover, the Monte Carlo method shows that information on the ion strike position can be obtained from the charge signals from the sensitive electrodes.

Optimization of the thickness of a ZnS/6LiF scintillator for a high-resolution detector installed on a focusing small-angle neutron scattering spectrometer (SANS-U)

This study involves the upgrade of a high-resolution position-sensitive detector (HR-PSD) installed on the small-angle neutron scattering spectrometer (SANS-U) at the Japan Atomic Energy Agency. By using both neutron lenses and the HR-PSD, the accessible low-Qlimit can be extended to the order of 10−4 Å−1[Qis the magnitude of the scattering vector defined byQ= (4π/λ)sinθ, where λ and 2θ are the wavelength and the scattering angle, respectively]. The HR-PSD consists of a cross-wired position-sensitive photomultiplier tube (PSPMT) and a commercial ZnS/6LiF scintillator. To improve the experimental efficiency of focusing small-angle neutron scattering (FSANS) experiments, a high-performance ZnS/6LiF scintillator developed at the Japan Atomic Energy Agency has been utilized. For the PSPMT and data-acquisition system installed on SANS-U, the thickness of the ZnS/6LiF scintillator was optimized by measuring the thickness dependence of the pulse-height spectra. Under the experimental conditions of SANS-U, the optimum thickness of the ZnS/6LiF scintillator (ZnS:6LiF = 2:1) was determined to be 0.433 mm by measuring the total counts and peak positions of the pulse-height spectra. Installation of the optimized ZnS/6LiF scintillator improved detection efficiency by 1.39 times over that of a commercial scintillator at the same level of background counts andQresolution in FSANS experiments.

Modernization of the small-angle neutron scattering spectrometer SANS-U by upgrade to a focusing SANS spectrometer

The small-angle neutron scattering spectrometer SANS-U at the research reactor (JRR-3) of the Japan Atomic Energy Agency, Tokai, Japan, has been successfully upgraded. This major upgrade was undertaken in order to install a high-resolution position-sensitive detector consisting of a cross-wired position-sensitive photomultiplier tube combined with a ZnS/6LiF scintillator on the SANS-U spectrometer. Without changing the total length of the spectrometer, the aim was to extend the accessible low-Qlimit (Qis the magnitude of the scattering vector) and to shorten the measurement time by employing focusing small-angle neutron scattering (FSANS). By using both spherical MgF2biconcave lenses and the new high-resolution position-sensitive detector, the accessible low-Qlimit was extended from 2.5 × 10−3to 3.8 × 10−4 Å−1. As a result, SANS-U can continuously cover a wideQrange from 3.8 × 10−4to 0.35 Å−1with a wavelength of 7 Å. FSANS can be utilized not only to improve the accessible low-Qlimit but also to increase the intensity of incident neutrons passing through the sample in the conventionalQrange from 2.5 × 10−3to 0.35 Å−1. The use of `high-intensity' FSANS also allowed a reduction of the measuring time by approximately 1/3.16 by increasing the incident neutron intensity.

Performance studies on high pressure 1-D position sensitive neutron detectors

The powder diffractometer and Hi-Q diffractometer at Dhruva reactor make use of five identical 1-D position sensitive detectors (PSDs) to scan scattering angles in the range 3° to 140°. In order to improve the overall throughput of these spectrometers, it is planned to install a bank of 15 high-efficiency and high-resolution PSDs arranged in three layers with five PSDs in each layer. With each high pressure PSD (3He 10 bar + Kr 2 bar) showing the efficiency gain of 1.8 at 1.2 A, detector bank is expected to show overall gain of 5.5 times the present detection efficiency and reduction in data collection time by equivalent factor. The 1-D PSDs are developed in batches of five, and are characterized so that all PSDs operate at uniform parameters such as position resolution, uniformity of efficiency and linearity of response. Position spectrum indicates the differential position resolution to be ∼1 mm and integral position resolution to be 3–4 mm. Broadening of position spectrum at the extreme end of sensitive length of PSD is analysed using fine shift of the beam. Dependence of position resolution and dynamic range of output pulse on the input impedance of pre-amplifier is also presented.

A Tunable External Cavity Laser Diode Possessing a Stable Wavelength

In this work we describe a simple external-cavity laser diode equipped with a feedback control system, in which a high-resolution position-sensitive detector detects the slight misalignment of the light within the cavity. Our system not only provides a stable wavelength that can be tuned within a maximum scanning range of 1.87 nm, but also allows for faster scanning, through precise control of the reflection angle within the cavity. The simultaneous controls on the rotation-angle of the external mirror and the injection current enabled us to realize continuous wavelength-tuning.

Large-aperture automatic focimeter for the measurement of optical power and other optical characteristics of ophthalmic lenses.

We propose an optical apparatus enabling the measurement of spherical power, cylindrical power, and optical center coordinates of ophthalmic lenses. The main advantage of this new focimeter is to provide a full bidimensional mapping of the characteristics of ophthalmic glasses. This is made possible thanks to the use of a large-area and high-resolution position-sensitive detector. We describe the measurement principle and present some typical mappings, particularly for progressive lenses. We then discuss the advantages in terms of speed and versatility of such a focimeter for the measurement of complex lens mappings.

The new high resolution ultra small-angle neutron scattering instrument at the High Flux Reactor in Grenoble

In 1998, the combined Interferometer and Ultra Small Angle Neutron Scattering (USANS) instrument S18 at the 58 MW High Flux Reactor at the Institute Laue-Langevin in Grenoble (France) started operation. The instrument has been upgraded to allow more advanced neutron optics experiments for fundamental, nuclear and condensed matter physics. The new supermirror guide along with the two channel cut silicon perfect crystals, configured as an advanced high resolution Bonse-Hart camera, provides optimal intensity conditions. A large range of wavelengths is accessible by variations of the Bragg angle and by using different reflecting planes of a properly cut silicon monochromator block in combination with different channel-cut analyzer crystals. The fine adjustment analyzer system is achieved by an advanced piezo drive, which has an accuracy of 0.036 seconds of arc. The basic features of the USANS camera, which takes advantage of a new tail suppression method, and the results of various test measurements concerning intensities, long term stability and the accessible wavelength range will be presented. A high resolution position sensitive detector can either be used to analyze beam profiles or to perform neutron radiography experiments.

Development of high-resolution single-ion PSD using random access memories

Using heavy-ion microbeam, we have examined the feasibility of a Static Random Memory (SRAM) as an in situ Position Sensitive Detector (PSD) with bit-cell size resolution for extremely low current ion beams. It is found that SRAMs are promising candidates for high-resolution PSD to diagnose an extremely low current ion microbeam.

Neutron topography of interferometer output beams

Intensity distributions of the output beam of a perfect-crystal neutron interferometer recorded by a high-resolution position-sensitive detector are analysed. It was found that the interference pattern visibility is determined by an incoherent foundation of constant amplitude (no Moiré fringes were observed). A hypothesis about vibrations of the interferometer plates is presented. A modification of the setup following from this supposition increases the interference pattern visibility from 40% to 65–70%.

Phase-space measurement of stored electron beam at the Cornell Electron Storage Ring using a combination of slit array and CCD detector

A new technique for fast phase-space measurement has been developed and tested during a recent APS/CHESS undulator run. A measurement time of a few seconds was obtained by using a slit array and a high-resolution position sensitive detector system. The detector system consists of a CdWO4 scintillation crystal, an optical imaging system, and a CCD detector. The short measurement time increases the measurement accuracy by reducing the effects from the instabilities of the electron beam in storage ring. The vertical emittance at the Cornell Electron Storage Ring in single-bunch and low-current mode was measured, and reasonable agreement with the expected values for both source size and source divergence were obtained (σy=75 μm and σy′=12 μrad). The effects of the finite size of the first slit on the measurement results are discussed, and a comprehensive data analysis procedure is described.

X-ray detectors for structure investigations constructed at JINR

The performance characteristics of a few high resolution position-sensitive detectors constructed at JINR are presented. The detectors supplied with original software operate with an IBM PC/AT. One of these devices has been succesfully applied for protein molecule structure investigations and the other for studies of the structure-forming process during combustion. The preliminary parameters of the high count rate MWPC with parallel electronics and the testing results of the microstrip detector are given.

CCD X-ray detectors: Opportunities and challenges

Charge coupled device (CCD) arrays are showing considerable promise for a variety of X-ray imaging applications. Performance characteristics such as high dynamic range, versatile readout and data-storage modes, and time-resolved capabilities, present interesting opportunities for new kinds of experiments on high-brilliance sources. We illustrate some of these possibilities with results of our recent synchrotron radiation studies using CCDs as high-resolution position-sensitive detectors. While important hurdles have already been overcome, several challenges remain for the effective exploitation of CCDs in X-ray applications. Among these are requirements for further increases in spatial resolution, radiation hardening, and very-high-speed data acquisition. Ongoing developments and future directions are discussed in this context.

Use of CCD detectors for spectroscopy and scattering experiments

The application of CCD detectors in X-ray synchrotron radiation experiments is described. Performance characteristics such as high dynamic range, versatile readout and data storage modes, and time-resolved capabilities promise interesting possibilities for future experiments on high-brilliance sources. The operation of CCDs as high-resolution position-sensitive detectors, used in conjunction with dispersive optics, is illustrated by recent results on near-edge reflectivity from multilayers and magnetic absorption experiments with circularly polarized X-rays.

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>

Charge state dependence of [formula omitted] for ions in very thin targets

Relative stopping powers of 3 MeV/u He, Li and C ions have been measured in very thin carbon targets (2–26 μg/cm 2). Energy losses were measured using a high resolution position sensitive detector (PSD) in the focal plane of a magnetic spectrometer, so that only one charge state (the incident charge state) was detected. As expected for fully stripped light projectiles in C targets, the stopping power data for He and Li ions scale as Z 1 2 to within our ~1% experimental precision. However, for C ions, charge-changing effects are found to influence the stopping considerably. The evolution of the charge-state distribution as a function of foil thickness for 3 MeV/u C ions in C foils has been determined in prior experiments. A two-component charge state model is used to predict the corresponding evolution of stopping power for both C 6+ and C 5+ ions, using these charge state data. Comparison of the model with our observations of dE dx show that charge-changing events themselves contribute significantly to stopping in thicker foils, even in the present high velocity regime. From our data we extract the stopping cross sections S 00 and S 11 for the fully stripped and one-electron ions in the absence of charge-changing events, and the energy loss U = (2.3 ±0.2) keV undergone in the charge-change cycle C 6+ C 5+. A higher order Z 1 effect of ∼ −2.8% is observed in the total stopping cross-section S o for the fully stripped ion. This is comparable with the usual Bloch term plus Lindhard's polarisation term, which together yield a −2.0% effect. However, the presence of charge-changing energy losses means that the polarisation theory gives only a very sketchy estimate of the appropriate higher order correction for heavy ions.

A High Resolution Position Sensitive Detector for Ultraviolet and X-Ray Photons

A new type of position sensitive detection system for ultraviolet and x-ray photons and for particles is described. A compact laboratory model with one-dimensional readout was constructed and tested. The full width at half maximum response to single x-rays was typically 0.13 mm, but the position determination accuracy was comparable to the channel center-to-center spacing of 0.053 mm. The detection system can be readily adapted to two-dimensional readout. Potential applications of this device for single-photon and flux counting in ultraviolet and x-ray astronomy are discussed.