Position Sensitive Detector System Research Articles

Near-zero beam drift laser tracking and measurement system with two-stage compression structures.

This paper introduces a scheme of near-zero beam drift tracking technology with two-stage compression structures for the coordinate accuracy measurement of a laser tracker. The Galileo telescope system, with a magnification of 21.43, is designed to compress the beam drift in a dual-frequency interferometer. The azimuth and pitch of the beam drift are compressed to 2.41in. and 2.92in., and the compression rates are 95.0% and 91.9%, respectively. The improved four degrees of freedom position-sensitive detector system is used to further compress the beam drift. The peak-to-peak value of the beam drift is 0.9in. in the azimuth direction and 2.1in. in the pitch direction. The standard deviation of azimuth is within 0.15in, and the pitch is within 0.43in. The coordinate accuracy of the laser tracker can be improved 6.85 parts per million by simulation. The developed two-stage compression near-zero beam drift system can be used in the laser tracker to realize large-scale precision instrument geometric measurement.

Electron Capture by Proton Beam in Collisions with Water Vapor

In low energy ion-molecule collisions, electron capture is one of the most important channels. A new experimental setup was developed to study the electron capture process using low-energy ion beams extracted from an electron cyclotron resonance (ECR) plasma-based ion accelerator. Experiments were carried out with the proton beam colliding with water vapor in the energy range of 70–300 keV. Capture events were detected using a position-sensitive detection system comprising micro channel plates (MCPs) and a delay line detector (DLD). These e-capture events can be a result of pure capture reactions as well as transfer ionization. The capture cross section was found to decrease sharply with the beam energy and agreed well with previous measurements. The setup was also used to detect the events that gave rise to the single and multiple e-capture (integrated over all recoil-ion charge states) of C4+ ions. The capture cross-sections for one, two, three, and four electrons were measured for 100 keV C4+ ions. The ratio of multielectron capture yield to that for single e-capture decreased with the number of captured electrons.

Overview of planned upgrade to the secondary spectrometer of TOSCA

We describe a proposed upgrade to the indirect-geometry broad-band chemical spectrometer TOSCA at the ISIS Neutron and Muon Source, UK. By replacing the secondary spectrometer of the instrument, we expect a gain in detected intensity of an order of magnitude, improved spectral resolution over the entire energy range of the instrument and an improved signal-to-noise ratio. The new secondary spectrometer consists of 14 analyser modules, each constituted of a large, curved pyrolytic graphite analyser, a beryllium filter and a position-sensitive detector system. We present the prospective design and expected performance of the new analyser module as calculated from ray-tracing simulations. The improved performance will develop the instrument capabilities to tackle new and challenging experiments and ensure that TOSCA remains highly competitive in the years to come.

Image quality of list-mode proton imaging without front trackers

List mode proton imaging relies on accurate reconstruction of the proton most likely path (MLP) through the patient. This typically requires two sets of position sensitive detector systems, one upstream (front) and one downstream (rear) of the patient. However, for a clinical implementation it can be preferable to omit the front trackers (single-sided proton imaging). For such a system, the MLP can be computed from information available through the beam delivery system and the remaining rear tracker set. In this work, we use Monte Carlo simulations to compare a conventional double-sided (using both front and rear detector systems) with a single-sided system (only rear detector system) by evaluating the spatial resolution of proton radiographs (pRad) and proton CT images (pCT) acquired with these set-ups. Both the pencil beam spot size, as well as the spacing between spots was also adjusted to identify the impact of these beam parameters on the image quality.Relying only on the pencil beam central position for computing the MLP resulted in severe image artifacts both in pRad and pCT. Using the recently extended-MLP formalism that incorporate pencil beam uncertainty removed these image artifacts. However, using a more focused pencil beam with this algorithm induced image artifacts when the spot spacing was the same as the beam spot size. The spatial resolution tested with a sharp edge gradient technique was reduced by 40% for single-sided (MTF10% = 3.0 lp/cm) compared to double-sided (MTF10% = 4.9 lp/cm) pRad with ideal tracking detectors. Using realistic trackers the difference decreased to 30%, with MTF10% of 4.0 lp/cm for the realistic double-sided and 2.7 lp/cm for the realistic single-sided setup. When studying an anthropomorphic paediatric head phantom both single- and double-sided set-ups performed similarly where the difference in water equivalent thickness (WET) between the two set-ups were less than 0.01 mm in homogeneous areas of the head. Larger discrepancies between the two set-ups were visible in high density gradients like the facial structures. A complete CT reconstruction of a Catphan module was performed. Assuming ideal detectors, the obtained spatial resolution was 5.1 lp/cm for double-sided and 3.8 lp/cm for the single-sided setup. Double- and single-sided pRad with realistic tracker properties returned a spatial resolution of 3.8 lp/cm and 3.2 lp/cm, respectively. Future studies should investigate the development of dedicated reconstruction algorithms targeted for single-sided particle imaging.

Rectified Gaussian noise estimation and its use in position sensitive detection systems

Noise estimation of an amplified sensor output is essential for not only operating the position sensitive detection (PSD) system efficiently but also for improving accuracy. The noise can vary from device to device and depends on the operating environment; thus, its estimation should be conducted in real time. However, the rectified noise owing to the limited dynamic range of the analogue-to-digital converter makes this estimation challenging. This Letter presents the use of noise parameter estimation, such as non-uniform offset compensation, detection threshold calculation, and variance estimation of a beam's estimated angular position in PSD systems. Moreover, the estimation of rectified Gaussian noise parameters is proposed. Experiments with the implemented PSD system verify the performance of the proposed estimation method for the rectified Gaussian noise characteristics and the offset compensation method for the estimated beam position.

Camera-based sample-position detection and control for microgravity electrostatic levitation.

This paper presents a method for high-speed sample detection and position control in an electrostatic levitator. The algorithm uses images acquired from two charge coupled device cameras and allows for robust and reliable detection of the sample position under various process conditions. The results show improvements over position sensitive detector systems especially under harsh environments and during autonomous operation under microgravity conditions. The position of samples with a radius from 0.6 mm to 1.1 mm is detected in three dimensions with an accuracy of ±40 μm inside a 7 mm × 7 mm × 7 mm levitation area. The two orthogonally arranged cameras, recording images at a resolution of 260 px × 260 px, are used to calculate the position every 5 ms. The control model and the corresponding position controller for the three axes are presented as well. The system was successfully tested in the laboratory and under microgravity conditions at the drop tower, during parabolic flights, and on the MAPHEUS sounding rocket.

Optimization-Based Calibration Process for Position-Sensitive Detector Systems

In this paper, a calibration process for position-sensitive detector (PSD) systems is proposed. In a PSD system using a quadrature detector (QD), various error sources including the QD, circuit components, and mechanical misalignment that appear in actual implementation introduce inaccuracies in the beam position estimation. The error pattern can be non-linear in the beam power, and non-uniform in the beam position. To calibrate the PSD and enhance the estimation accuracy, this work proposes an optimization-based calibration process. The proposed calibration process is comprehensive, correcting all errors at once in the final assembly state, which can reduce the calibration time and cost. Moreover, the result of the calibration is stable with respect to variations in the beam power, gain stage, and beam position. The impressive enhancement in accuracy and stability of beam position estimation is demonstrated experimentally.

Analysis and Adjustment of Positioning Error of PSD System for Mobile SOF-FTIR.

A PSD-based solar spot position detection system is developed for solar tracking closed-loop control of mobile SOF-FTIR (Solar Occultation Flux method based on Fourier Transform Infrared spectrometer). The positioning error factors of PSD (position sensitive detector) are analyzed in detail. A voltage model for PSD signal conditioning circuit has been established to investigate the noise factors. The model shows that the positioning error is mainly related to PSD dark current and circuit gain. A static voltage deduction calibration method based on genetic algorithm is proposed to eliminate the effect of dark current. The gain ratio between channels is calculated based on the fitting curve slope of discrete position data of PSD center point with different light intensity for circuit gain calibration. The positioning accuracy and precision are greatly enhanced, especially when the light intensity is weak, compared with uncalibrated results. The positioning accuracy of center, middle and edge areas of PSD can reach 0.14%, 0.49%, and 1.09%, respectively, after correction in the range of light intensity voltage from 40 mV to 20 V. The corresponding standard deviations of each region are 0.005, 0.009, and 0.014, respectively. The adjustment methods proposed in this paper improve both measurement accuracy and detection limit. The results demonstrate that the calibrated PSD positioning accuracy can meet the requirements of SOF-FTIR for solar tracking.

Laser Beam Position-Dependent PSD-Based Calibrated Self-Vibration Compensated Noncontact Vibration Measurement System

This paper explores the notion and efficacy of harnessing the advantages of position sensitive detector (PSD) in the paradigm of noncontact vibration measurements. The study peruses an innovative foray into the domain of calibrated vibration measurement systems, wherein a first-of-its-kind strategy has been explored to nullify the self-vibration effect of the PSD platform by incorporating a micro-elctromechanical system digital accelerometer. The self-vibration compensated system has been designed and experimentally validated through NI-CompactRIO. The proposed system has been calibrated with a single axis Brüel&Kjær piezoelectric accelerometer. The system was observed to yield a maximum absolute error of 0.34 Hz in the measuring frequency range of 20–600 Hz. Furthermore, the system was observed to effectively measure displacement in the range of 2.32– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1300~\mu \text{m}$ </tex-math></inline-formula> with a maximum relative error of 2.7% across the span of gain settings varied at designated set of frequencies tested. Successive measurements yielded good repeatability characterized by a maximum standard deviation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 ~\mu \text{m}$ </tex-math></inline-formula> . A commendable system linearity was also achieved for its intended range of measurement as characterized by a correlation coefficient of 99.8%. The accuracy and robustness of the noncontact PSD system coupled with its inherent simplicity of system integration establishes itself as a potent and cost-effective tool in the realm of vibration measurements of highly sensitive systems susceptible to microvibrations (<1 kHz) compared to its more expensive prevalent noncontact laser Doppler vibrometer counterparts. The developed system also exhibits pivotal significance in critical application areas where human involvement is not advisable.

Active Target for α-Particle Condensation Studies in 16O

An active target has been developed for studying the Hoyle like states in 16O. It is a position and time sensitive detector system based on the Low-Pressure Multy-Wire Proportional Chamber (LPMWPC) technique and Si detectors. The few Torr pressure of methyl ((OCH3)2CH2) serves as a working gas for the LPMWPC operation, and the oxygen atoms of the methyl molecules serve as an experimental target. The main advantage of this new target-detector system is a high sensitivity to the low-energy, highly ionizing particles, produced after photodisintegration of 16O, and the insensitivity to the γ-rays and low ionizing particles, which allows one to detect only the products of the nuclear reaction, which are studied. The threshold energies for detection of α particles and 12C nuclei are about 50 keV and 100 keV, respectively. Temporal and positional resolution of the LPMWPC modules was investigated with the use of the α-particle source. This paper discusses the architecture of the active target and the test results of the prototype MWPC detector. This installation has been constructed to study the cluster states at 15.1 MeV in 16O using the proton beams from the Yerevan proton cyclotron and the Compton backscattered photon beams of the ELI-NP facility.

Spatial and Compositional Biases Introduced by Position Sensitive Detection Systems in APT: A Simulation Approach.

Due to the low capacity of contemporary position-sensitive detectors in atom probe tomography (APT) to detect multiple events, material analyses that exhibit high numbers of multiple events are the most subject to compositional biases. To solve this limitation, some researchers have developed statistical correction algorithms. However, those algorithms are only efficient when one is confronted with homogeneous materials having nearly the same evaporation field between elements. Therefore, dealing with more complex materials must be accompanied by a better understanding of the signal loss mechanism during APT experiments. By modeling the evaporation mechanism and the whole APT detection system, it may be possible to predict compositional and spatial biases induced by the detection system. This paper introduces a systematic study of the impact of the APT detection system on material analysis through the development of a simulation tool.

A compact scintillator based position sensitive detector system for gamma ray tracking applications

Abstract A Cerium doped Lutetium Yttrium Orthosilicate (LYSO) crystal based precision gamma detection system has been developed using a position sensitive photomultiplier tube, with minimal pulse processing requirements. The assembly’s detailed characterization has been reported in this work. This kind of a setup with a precise spatial resolution can be very useful for scanning high purity germanium detectors that use pulse shape analysis algorithms for signal processing in gamma ray spectroscopy experiments. The highly pure LYSO crystal used here is custom-made and the overall setup including the multi anode readout photomultiplier tube is compact. The system has been tested for energy, timing and position information regarding gamma photons interacting within the crystal using a coincidence mechanism. Position sensitivity has been found to be in the anticipated range of a few millimeters. This kind of a detector can be used in various fields, vis-a-vis, medical imaging, radioactive waste management, nuclear proliferation control, and various applications that deal with precisely identifying and locating radioactivity.

APCAD—Analysis program for the continuous-angle DSAM

We present a novel method for the analysis of Doppler-broadened γ-ray lineshapes observed by position-sensitive detector systems with the purpose to determine nuclear level lifetimes. This advance of the well-known Doppler-Shift Attenuation Method (DSAM) is specifically tailored to experiments employing γ-ray tracking detectors and takes advantage of the position resolution of these detector systems. The novel continuous-angle Doppler Shift Attenuation Method (caDSAM) is implemented in the comprehensive computer program APCAD for the calculation of Doppler-broadened γ-ray lineshapes, their fit to experimental data and extraction of level lifetimes. Extensions of the method qualifying it for measurements with radioactive and relativistic ion beams as well as for the measurement of “long” level lifetimes of the order of ∼200 ps are presented.Program summaryProgram Title: APCAD, StopSimProgram Files doi:http://dx.doi.org/10.17632/4hzzcvx2p7.1Licensing provisions: Creative Commons by 4.0 (CC by 4.0)Programming language: C++Supplementary material: User’s manual, installation notes, example dataNature of problem: Determination of nuclear level lifetimes from Doppler-broadened γ-ray lineshapes (DSAM)Solution method: Semi-analytical calculation of Doppler-broadened lineshapes as function of γ-ray energy and γ-ray observation angleExternal routines/libraries: ROOT, Geant4Subprograms used: CLX, DWEIKORestrictions: Only direct feeders can be considered in the current version (decay chains of length two only)Unusual features: Position resolution of γ-ray tracking detectors is exploited

New Very Small Angle Neutron Scattering (VSANS) Instrument

The design of a new Very Small Angle Neutron Scattering (VSANS) Instrument for use in National Institute of Standards And Technology (NIST) will be discussed. This instrument is similar to a shorter instrument we designed and delivered to ANSTO in Australia called the Bilby SANS instrument. The NIST VSANS and the ANSTO Bilby SANS instruments have very similar dimensions for length and diameter and have similar requirements for internal detector motion, top access port, walkway supports, and ports; however, the Bilby SANS instrument vacuum requirement was lower (7.5×10-5 Torr) and the entire (60,000 pound) vessel was required to move 1.5 meters on external rails with a repeatability of 100 um, which ADC achieved. The NIST VSANS length is 24 meter, internal diameter 2.3 meter with three internal carriages.The NIST VSANS instrument, which covers the usual SANS range will also allow configuration to cover the range between q ∼⃒ 10-4 A-1 to 10-3 A-1 with a sample beam current of (104 neutrons/s). The key requirements are a second position-sensitive detector system having a 1 mm pixel size and a longer sample-detector flight path of 20 m (i.e., a 40 m instrument).

Fragmentation of molecules under charge-changing collisions of a few MeV heavy ions

We investigated molecular fragmentation of CO and C2H2 molecules by impact of various fast heavy ions. Fragment ions produced in electron capture and loss collisions of projectile ions were measured in coincidence with final projectile charge states. Data acquisition using position sensitive detection system allows us to obtain 3D momentum imaging of fragment ions and kinetic energy release (KER) in various charge-changing collisions. It was found that the KER spectra show strong dependence on the type of charge-changing collisions. This may be caused by the difference of impact parameters associated with individual charge-changing collisions. Moreover we revealed the different fragmentation pathway between ion impacts and photoionization.

Employing digital pulse processing electronics for the readout of a Si(Li)—Compton—polarimeter for the SPARC collaboration

The future x-ray spectroscopy and polarimetry experiment program of the SPARC collaboration at GSI and FAIR relies strongly on the availability of two-dimensional position-sensitive, energy- and time-dispersive thick semiconductor detector systems, including the appropriate signal processing electronics. To meet these demands, the development of a compact and scalable data acquisition system that has higher rate acceptance compared to commercial VME electronics by employing digital pulse processing electronics was started.

Data Analysis of Transient Fire Angle Test System Based on Wavelet Theory

Aimed at the noise of PSD (position sensitive detector) system signal,In view of the PSD system signal characteristic, the wavelet way is provided for filtering and de-noising to improve system precision. Suitable wavelet processing method db10 is selected, The simulation results indicate that the algorithm can be a better way to filtering and de-noising.

Development of two-dimensional position sensitive detector systems using multi-pixel photon counters for neutron experiments

Neutron scattering experiments are indispensable to the structural analysis of many types of condensed matter and in the development of advanced materials. A high resolution detector system and a high counting rate detector system, both utilizing a neutron scintillator and multi-pixel photon counters (MPPCs), have been developed at the High-Energy Accelerator Research Organization (KEK). These systems will be used in the BL16 and BL06 neutron scattering instruments at the Material and Life Science Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). The high resolution detector is an MPPC position-sensitive detector (MPS) with a 105×128mm2 detection area and has positional resolution of 1mm. The high counting rate detector is an MPPC Pixel detector (MPIX) with a 320×40mm2 detection area. The maximum counting rate is 4 million counts per second (Mcps).

Fabrication of High-Resolution ${\hbox {Lu}}_{2}{\hbox {O}}_{3}{:}{\hbox {Eu}}$ X-Ray Scintillator by Physical Vapor Deposition

A new structured scintillator was developed that will stop significantly more of the incident X-rays without sacrificing spatial resolution. We have recently demonstrated that it is possible to deposit Lu2O3:Eu in a microcolumnar form using electron beam (e-beam) physical vapor deposition (EBPVD) technique. This new structured Lu2O3:Eu scintillator can have a huge impact on X-ray imaging applications including medical imaging, nondestructive testing and hard X-ray microtomography (XMT). Thin film fabrication of Lu2O3 doped with 5% europium was carried out by means of EBPVD. Uniform and stoichiometrically balanced films several microns thick were grown on various kinds of substrates. Their morphology was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Scintillation decay, afterglow, spatial resolution and light conversion efficiency were analyzed. A selected set of films was integrated into position-sensitive detection systems to determine their efficacy for synchrotron and laboratory X-ray source-based high-resolution microtomography.

High Dynamics and Precision Optical Measurement Using a Position Sensitive Detector (PSD) in Reflection-Mode: Application to 2D Object Tracking over a Smart Surface

When related to a single and good contrast object or a laser spot, position sensing, or sensitive, detectors (PSDs) have a series of advantages over the classical camera sensors, including a good positioning accuracy for a fast response time and very simple signal conditioning circuits. To test the performance of this kind of sensor for microrobotics, we have made a comparative analysis between a precise but slow video camera and a custom-made fast PSD system applied to the tracking of a diffuse-reflectivity object transported by a pneumatic microconveyor called Smart-Surface. Until now, the fast system dynamics prevented the full control of the smart surface by visual servoing, unless using a very expensive high frame rate camera. We have built and tested a custom and low cost PSD-based embedded circuit, optically connected with a camera to a single objective by means of a beam splitter. A stroboscopic light source enhanced the resolution. The obtained results showed a good linearity and a fast (over 500 frames per second) response time which will enable future closed-loop control by using PSD.