Two-dimensional Position Sensitive Detector Research Articles

Two-dimensional position sensitive neutron detector

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

Development of position-sensitive neutron detector based on scintillator

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

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

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

A flux- and background-optimized version of the NanoSTAR small-angle X-ray scattering camera for solution scattering

A commercially available small-angle X-ray scattering camera, NanoSTAR from Bruker AXS, has been modified to optimize its use for weakly scattering solution samples. The original NanoSTAR is a pinhole camera with two Göbel mirrors for monochromating and making the beam parallel, and with a two-dimensional position-sensitive gas detector (HiSTAR) for data collection. The instrument has one integrated vacuum. It was constructed for position-resolved studies and thus has a small beam size at the sample position. In the present work, the instrumental configuration has been optimized by numerical calculations based on phase-space analysis and Monte Carlo simulations in order to obtain a higher flux. This has led to a setup in which the beam at the sample is larger and the collimation part of the instrument is longer, so that divergence of the beam is similar to that of the original camera. An extra pinhole is included after the Göbel mirrors to make the beam size well defined after the mirrors. The camera thus has genuine three-pinhole collimation. The use of electron-microscope pinholes minimizes parasitic scattering. At the University of Aarhus, the modified camera is installed on a powerful rotating-anode X-ray source (MacScience 6 kW Cu with a 0.3 × 0.3 mm effective source size). Measurements have been performed on a wide variety of weakly scattering samples, such as surfactant micelles, homopolymer solutions, block copolymer micelles, proteinsetc. The data are routinely converted to absolute scale using the scattering from water as a primary standard. The standard configuration covers the range of scattering vectors from 0.01 to 0.35 Å−1with a flux of 1.7 × 107photons s−1for CuKα radiation at a generator power of 4.05 kW. The camera is easily converted to a high-resolution version covering 0.0037 to 0.22 Å−1with a loss of flux of about a factor of 10, as well as to a position-resolved version.

Design and performance of a two-dimensional multi-wire neutron detector with a sensitive area of 50×50 cm 2 and a spatial resolution of ∼2×2 mm 2

One two-dimensional position-sensitive multi-wire gaseous detector for small-angle neutron scattering (SANS), reflectometry and high-resolution diffractometry has been developed at the GKSS research center in co-operation with DENEX GmbH. The counter with a sensitive area of 500×500 mm 2 has been designed to be used in the reflectometer REFSANS being built at the new high flux reactor FRM-II. Tests of the detector with an 55Fe-source, cold neutrons and γ-radiation are presented.

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

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

A new detector system for radioactive ion beam experiments at the focal plane of the recoil mass spectrometer HIRA at NSC

7Be radioactive ion beam (RIB) has been produced by an in-flight separation technique using the recoil mass spectrometer Heavy Ion Reaction Analyzer (HIRA) at NSC. To carry out nuclear reaction studies using the low-intensity RIB, a compact geometry detector system has been installed at the HIRA focal plane. The new detector setup consists of a Multi-Wire Proportional Counter (MWPC) followed by a DE-E detector telescope. The MWPC is used for obtaining the RIB profile and normalization. Fast timing signal of the MWPC is also used for the time-of-flight measurements for correction of energy spread of the RIBs in event mode. The detector telescope consists of a gas ionization chamber which gives energy loss (DE), followed by a two-dimensional position-sensitive silicon detector which gives residual energy and position. The telescope provides particle identification, energy and reaction angle information. The measured position resolution of the MWPC is about 0.9 mm (FWHM). The detector setup has also been used in stable beam experiments as well where the MWPC provides mass spectrum of the recoils at the RMS focal plane according to their position.

A multi-crystal spectrometer with a two-dimensional position-sensitive detector and contour maps of resonant Kβ emission in Mn compounds

A newly constructed multi-crystal X-ray spectrometer is described and its application to resonant inelastic X-ray scattering (RIXS) study on several Mn compounds are presented. The apparatus features a use of a two-dimensional position-sensitive proportional counter as well as five cylindrically bent rectangular Ge (4 4 0) crystals with 35 mm×100 mm in size, whose radius of curvature is 550 mm. Diffracted X-rays from each crystal are horizontally dispersed and vertically focused onto different portion of the detector, and spectra are obtained by adding all the reflections from five crystals. Significant improvements in sensitivity have made it possible to present RIXS data as contour maps over wide energy ranges in both excitation and emission. RIXS contour maps for Kβ emission from MnO, Mn 2O 3, MnO 2, and KMnO 4 are presented and their implications are discussed. In particular, it is stressed that near-resonant inelastic X-ray scattering process contributes significantly to fluorescence as well as fluorescence excitation spectra.

First realisation of a three-dimensional refraction contrast computerised neutron tomography

We performed tomographic investigations of a sample with a special double crystal diffractometer (DCD) using only the refraction of a neutron beam as imaging signal. Up to now refraction contrast tomographies with DCDs have been performed with the standard detectors and linear position sensitive detectors (PSD). Especially the combination of a bent crystal type DCD with a PSD saved exposure time and increased the accuracy of the reconstructed image. However, the reconstructed objects had to be (high) slices of an object (having congruent cross sections in the height) due to the lack of any vertical resolution. Hence only two-dimensional slices of samples could be reconstructed and imaged. As the refraction effect is measured in a horizontal plane of scattering, other refraction angles out of that plane of scattering could be neglected. Therefore, a three-dimensional reconstruction of the sample volume becomes possible with a two-dimensional position sensitive detector. First results achieved by this set-up using the refraction contrast method will be given.

A neural network device for on-line particle identification in cosmic ray experiments

On-line particle identification is one of the main goals of many experiments in space both for rare event studies and for optimizing measurements along the orbital trajectory. Neural networks can be a useful tool for signal processing and real time data analysis in such experiments. In this document we report on the performances of a programmable neural device which was developed in VLSI analog/digital technology. Neurons and synapses were accomplished by making use of Operational Transconductance Amplifier (OTA) structures. In this paper we report on the results of measurements performed in order to verify the agreement of the characteristic curves of each elementary cell with simulations and on the device performances obtained by implementing simple neural structures on the VLSI chip. A feed-forward neural network (Multi-Layer Perceptron, MLP) was implemented on the VLSI chip and trained to identify particles by processing the signals of two-dimensional position-sensitive Si detectors. The radiation monitoring device consisted of three double-sided silicon strip detectors. From the analysis of a set of simulated data it was found that the MLP implemented on the neural device gave results comparable with those obtained with the standard method of analysis confirming that the implemented neural network could be employed for real time particle identification.

Data analysis process of a toroidal analyzer for electron–ion collision experiments

A toroidal analyzer has been developed to measure angular differential cross sections for electron scattering in electron–ion collisions. Energy and angular dispersed electron images are recorded by using a two-dimensional position sensitive detector. Operation and calibration of the analyzer are described with particular emphasis on a procedure to deduce the differential cross sections from the acquired two-dimensional data. Angular differential cross sections for elastic scattering of electrons from Ar7+ and Ar8+ ions are presented in the angular range from 34° to 85° at a collision energy of 100 eV in the center of mass frame.

Nuclear Dynamics of Core-Excited and Ionized Small Polyatomic Molecules Probed by Multiple Coincidence Momentum Imaging Technique

Our recent studies on nuclear dynamics of core-excited and core-ionized molecules probed by a multiple coincidence momentum imaging technique are reviewed. This technique consists of a time-of-flight spectrometer with a multi-hit two-dimensional position sensitive detector and a supersonic jet. One can probe the symmetries and the nuclear motions of polyatomic molecules using this technique. As a specific example, we illustrate how to resolve the symmetries of the CO2 C 1s−12πu core-excited states, which split into two states, A1 and B1, due to D∞h → C2v symmetry lowering by the static Renner-Teller effect, and how to probe the nuclear motion caused in these states. We discuss also symmetry lowering D3h → C3v and D3h → C2v initiated by the B 1s → 4a2'' excitation and F 1s ionization, respectively, in the BF3 molecule and nuclear motions in these core-excited and ionized states.

Lattice sites of ion-implanted Cu atoms in diamond

Radioactive 67Cu atoms were accelerated to 60keV at the online isotope separator ISOLDE at CERN, and implanted into a type IIa natural diamond sample to a dose of 2×1012cm−2. The channeling of β−-particles and conversion electrons emitted in the decay of 67Cu and 67Zn∗, respectively, were monitored about the three major axial directions with a two-dimensional position-sensitive detector. The electron emission channeling data were collected from the room-temperature-implanted sample and after annealing at 1200K.The observed channeling patterns were fitted with simulations based on the many beam formalism of electron motion through a crystal lattice. In the as-implanted sample, 25% of the Cu atoms were located a mean, isotropic displacement of 0.25(5)Å from substitutional sites, and the remainder, fR=75%, at sites that gave an isotropic emission yield. Annealing at 1200K results in enhanced axial and planar channeling effects. The fits to the data yield either a fraction f1=45(5)% of Cu atoms located 0.24(4)Å from substitutional sites and fR=57%, or a fraction f1=10(2)% at substitutional sites, a fraction f2=50(5)% at mean isotropic displacement of 0.5Å from substitutional sites, and a ‘random’ fraction fR=40%.

High-counting-rate and high-position-resolution neutron imaging detectors using short-lifetime phosphors with crossed-fiber readout

In order to obtain high-counting-rate and high-position-resolution neutron imaging, two-dimensional neutron position sensitive detectors using short-lifetime phosphors with crossed-fiber readout were developed. In these detectors, 7Li 2 10B 4O 7 ( 7L 10BO) was used as the neutron converter, the phosphor Y 2SiO 5 (lifetime ∼40 ns) and other organic phosphors with lifetimes of less than 10 ns were also used. Crossed-wavelength-shifting fibers were arranged on and under the phosphor/neutron converter sheet. Light generated in the phosphor sheet was detected by the few fibers surrounding the neutron interaction point. The X and Y position of the neutron interaction were determined by a double coincidence photon counting method. By carrying out a series of fundamental experiments for the imaging detector, it was determined that a position resolution of less than 0.5 mm could be obtained with a 0.25 mm thick Y 2SiO 5/ 7L 10BO sheet and wavelength shifting fibers 0.5 mm×0.5 mm in cross-sectional area. Experiments carried out at a cold neutron radiography facility, with maximum neutron flux of 1×10 8 n/s/cm 2, confirmed that the detector could work at a counting rate of more than 3 Mcps/line.

A position sensitive detector for SPIDR—a mission to map the cosmic web

The primary goal of the Spectroscopy and Photometry of the IGM's Diffuse Radiation (SPIDR) mission is to detect and map the huge filamentary structures, the “cosmic web”, predicted to be present in the IGM. To accomplish this task the SPIDR instrument comprises six imaging spectrographs providing high-resolution spatial maps of IGM features in the critical OVI and CIV lines at both rest and red-shifted wavelengths. Each spectrograph uses a two-dimensional position sensitive microchannel plate detector to image UV dispersed by a normal incidence grating, encoding spectral and spatial information. Two-dimensional imaging is recovered by tomographic reconstruction of data from the slowly spinning spacecraft. The detector configuration utilizes an open faced microchannel plate stack coated with a UV photocathode. The conservative imaging requirements are met by a wedge and strip anode whose performance has been enhanced by using the image charge technique. Image charge provides a highly stable and predictable detector response which has enabled us to use software simulation to improve the linearity of the readout considerably.

Optimization of a micro-strip gas chamber as a two-dimensional neutron detector using gadolinium converter

A micro-strip gas chamber (MSGC) has been under development as a two-dimensional position sensitive detector for neutron scattering experiments at the high-intensity proton accelerator facilities. The MSGC requirements as a neutron detector are high counting rate, high detection efficiency, high positional resolution, stability and large area coverage. The purpose of this paper is to verify the properties of Gadolinium as a MSGC converter. The arrangements of a capillary plate and MSGC gas pressure have been optimized by simulation of a Gadolinium converter. As a result of that, a position resolution of 160 μm and n/γ ratio of 200 were obtained at the gas pressure of 0.02 atm. In view of γ-ray sensitivity, the further improvement is required for practical applications.

Performance of the TPC with micro pixel chamber readout: micro-TPC

Micro-TPC, a time projection chamber(TPC) with micro pixel chamber($\mu$-PIC) readout was developed for the detection of the three-dimensional fine(sub-m illimeter) tracks of charged particles. We developed a two-dimensional position sensitive gaseous detector, or the $\mu$-PIC, with the detection area of 10$\times$10 cm${}^{2}$ and 65536 anode electrodes of 400 $\mu$m pitch. We achieved the gas gain of over 10000 without any other multipliers. With the pipe-line readout system specially developed for the $\mu$-PIC, we detected X-rays at the rate as high as 7.7 Mcps. We attached a drift cage with an 8 cm drift length to the $\mu$-PIC and developed a micro-TPC. We measured the basic performances of the micro-TPC and took three-dimensional tracks of electrons. We also developed a prototype of the MeV gamma-ray imaging detector which is a hybrid of the micro-TPC and NaI(Tl) scintillators and confirmed its concept by reconstructing the obtained data.

Polarized neutron reflectometry on lithographically patterned thin film structures

We report on the use of specular and off-specular polarized neutron reflectometry (PNR) for the study of magnetization reversal in patterned magnetic structures. We discuss the instrumental requirements and the measurement method and illustrate its potential by applying it to lithographically structured trilayer systems of the form (7.5 nm Au/20 nm Co/7.5 nm Au) prepared on oxidized Si wafers. In order to study the influence of the shape of the structures on the magnetic properties we prepared rectangular bars with a width of 1 μm and a length of 4 μm. The dots were arranged in a square lattice symmetry with a period of 10 μm. By using a two-dimensional position sensitive detector (PSD) we were able to record not only the specularly but also the off-specularly scattered intensity which has maxima at particular angles due to the in-plane periodicity of the discs. The second system that we studied is that of wires with a width of 2 μm and a period of 15 μm consisting of an exchange biased Co/CoO bilayer structure. By applying neutron spin analysis and monitoring the neutron reflectivity at a fixed angle of incidence as a function of an external magnetic field we were able to effectively study the magnetization reversal process in both systems.

Polarized neutron reflectometry on lithographically patterned thin film structures

We report on the use of specular and off-specular polarized neutron reflectometry (PNR) for the study of magnetization reversal in patterned magnetic structures. We discuss the instrumental requirements and the measurement method and illustrate its potential by applying it to lithographically structured trilayer systems of the form (7.5 nm Au/20 nm Co/7.5 nm Au) prepared on oxidized Si wafers. In order to study the influence of the shape of the structures on the magnetic properties we prepared rectangular bars with a width of 1 μm and a length of 4 μm. The dots were arranged in a square lattice symmetry with a period of 10 μm. By using a two-dimensional position sensitive detector (PSD) we were able to record not only the specularly but also the off-specularly scattered intensity which has maxima at particular angles due to the in-plane periodicity of the discs. The second system that we studied is that of wires with a width of 2 μm and a period of 15 μm consisting of an exchange biased Co/CoO bilayer structure. By applying neutron spin analysis and monitoring the neutron reflectivity at a fixed angle of incidence as a function of an external magnetic field we were able to effectively study the magnetization reversal process in both systems.

Development of a large area two-dimensional position sensitive Δ E− E detector telescope for material analysis

A large area two-dimensional position sensitive detector telescope has been designed and fabricated at NSC, New Delhi for performing ERDA based material characterization experiments. This gas ionization detector is working well with position resolution better than 2 mm and good z-separation in both high and low mass regions. Large solid angle is a pre-request to minimize the possible unwanted radiation damage during the measurement. The consequent kinematic broadening has been corrected by recording the position information. Two-dimensional position sensitivity has also been obtained. Possibility of controlled modification is shown in this work.