Circular Detector Research Articles

Design, fabrication and characterization of a front-etched micromachined thermopile for IR detection

This paper presents the design, fabrication and experimental results of a front-etched CMOS compatible micromachined thermopile IR detector. The N-polysilicon/Al thermocouples were embedded in a 2.5 µm thick SiO2–Si3N4–SiO2 sandwich membrane, and XeF2 front-side isotropic post-etching was adopted to release and thermally isolate the thermopile structure. Due to the isotropy of XeF2 etching, a lot of flexibility was allowed in etching window layout and thermopile structure design. Etching windows in the dielectric absorber area were designed to avoid cutting off the heat transfer path from the absorber to hot junctions, and aluminum strips were patterned in the absorber to ensure the temperature was uniform across the absorber area. Two different thermopile structures, circle and rectangle, were designed and fabricated to investigate detector performance with respect to the thermopile structure. The steady-state behavior of fabricated detectors was anticipated by thermal ANSYS simulation. Due to the fact that the circular structure can get a higher temperature difference between hot and cold junctions, the circular thermopile detector has a quicker response, two times higher responsivity and detectivity than the rectangular thermopile detector. The circular thermopile detector exhibits a responsivity of 102.0 V W−1, a detectivity of 9.2 × 107 cm Hz1/2 W−1 and a time constant of 16.8 ms, in air at room temperature.

Separation and aquatic toxicity of enantiomers of the organophosphorus insecticide O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN)

Enantioselectivity in separation and toxicity of chiral pesticides has become important research areas in environmental science, because these studies give a deeper insight into the environmental effect of chiral pesticides. In this study, enantiomeric separation of the organophosphorus pesticide and acaricide O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN) was investigated by chiral high-performance liquid chromatography (HPLC) with two chiral stationary phases. The racemate and separated enantiomers of EPN were tested for aquatic toxicities assay using Daphnia magna and zebrafish ( Danio rerio) embryo test. The enantiomers of EPN were completely separated on Chiralpak AD and Chiralpak AS columns coupled with a circular dichroism detector at 236 nm. Better separations were achieved with lower temperatures (e.g., 20 °C) and lower levels of polar modifiers (e.g., 1%). A significant difference was found between the enantiomers in their acute aquatic toxicity; the (+)-enantiomer was about 10 times more toxic than its antipode. On the contrary, the (−)-enantiomer induced crooked body, yolk sac edema and pericardial edema significantly more than (+)-enantiomer in the zebrafish embryo test. These results suggest that biological toxicity of chiral pesticides should be assessed by using their individual enantiomers with more comprehensive methods.

Geometric efficiency for a circular detector and a linear source of arbitrary orientation and position

A new axisymmetric radiation vector potential which is singular along its entire axis of symmetry is derived for a spherically symmetric point radiation source. This potential and a previously given non-singular point source potential are integrated to give radiation vector potentials for a straight linear source of constant strength. Analytical solutions are given for the geometric efficiency G of a line source and a circular disk detector when the line source is parallel to the detector axis. The analytical solution is also given for the case where the line source is parallel to the disk surface, such that the source axis and the detector axis intersect. All other cases are given as simple one-dimensional trigonometric integrals. Numerical results for G are given for all cases considered, and results given previously by Pommé for a line source parallel to the detector plane have been verified. The methods and vector potentials presented here can be adapted for calculations with many different geometries, and many results are applicable in other fields such as electromagnetism, gravity and fluid mechanics.

SU-GG-T-430: Normalized Bragg Peak Curves for Various Proton Energies in a Cylindrical Water Phantom: A Simulation with MCNPX and GEANT4 Monte Carlo Codes

Purpose: To simulate protoninteraction(energy from 60 to 250 MeV) in water using MCNPX version 2.7B Monte Carlo code to determine accurately proton ranges from Bragg peak. Method and Materials: A cylindrical water phantom (100cm length, 30cm radius), composed of 1000 packed circular sensitive detector discs (2cm radius, 1 mm thick) was used. A pencil beam source was incident on the surface of the cylinder in z direction. Tabular nuclear data from LA150N and LA150H libraries were used for neutrons and protons with 150 MeV, the LAHET physics code was used and the hadronic interactions were handled using the Bertini cascade model. The Vavilov model was used to account for charged‐particle straggling. Normal transport was performed for neutron,proton,photon, electron, deuteron, triton, helium‐3, alpha, and heavy ions. Light ion recoil was accounted for in the simulations and the cutoff energy for these particles was set to zero to prevent early termination of their transport. A 5cm × 5cm field size beam was also simulated. A total of 80,000 source histories were run for each simulation. Eleven sourceenergies were tested for the pencil beam and three sourceenergies were studied for the 5cm × 5cm field size beam. Results: Our MCNPX results were compared with GEANT4 results as well as the Continuing Slowing Down Approximation (CSDA) data from the United States National Institute of Standards and Technologies (NIST). The deviation in Bragg peak range was <1% of that calculated with the GEANT4 and <0.6% of the CSDA data. The entrance to peak dose ratios between the different codes were comparable for 150 and 200 MeV though larger difference was noted for 250 MeV beam. Conclusions: Our proton Bragg peak simulation results using MCNPX are in excellent agreement with GEANT4 as well as NIST data.

New area detector for atomic-resolution scanning transmission electron microscopy

A new area detector for atomic-resolution scanning transmission electron microscopy (STEM) is developed and tested. The circular detector is divided into 16 segments which are individually optically coupled with photomultiplier tubes. Thus, 16 atomic-resolution STEM images which are sensitive to the spatial distribution of scattered electrons on the detector plane can be simultaneously obtained. This new detector can be potentially used not only for the simultaneous formation of common bright-field, low-angle annular dark-field and high-angle annular dark-field images, but also for the quantification of images by detecting the full range of scattered electrons and even for exploring novel atomic-resolution imaging modes by post-processing combination of the individual images.

Direct Enantiomeric Separation of Chiral Pesticides by LC on Amylose Tris(3,5-dimethylphenylcarbamate) Stationary Phase under Reversed Phase Conditions

Amylose tris(3,5-dimethylphenylcarbamate) chiral stationary phase was used by liquid chromatography under reversed-phase conditions for the chiral separation of 20 pesticides, of which ten samples were separated directly under suitable conditions. The influence of mobile phase composition and column temperature from 0 to 40 °C on the separation was investigated. The mobile phases were methanol/water or acetonitrile/water at a flow rate of 0.5 mL min−1 with UV detection at 230 nm. The two enantiomers of fenamiphos, terallethrin, fenoxaprop-ethyl, benalaxyl and lactofen could obtain base separation under optimized conditions, while the enantiomers of quizalofop-ethyl, metalaxyl, napropamide, fluroxypyr-meptyl and 2,4-D-ethylhexyl got partial separation. The retention factors (k) and selectivity factor (α) for the enantiomers of most investigated pesticides decreased with increasing the temperature. The lnα–1/T plots for enantiomers of chiral pesticides were linear at the range of 0–40 °C except for that of metalaxyl, fenoxaprop-ethyl and 2,4-D-ethylhexyl enantiomers in methanol/water. The thermodynamic parameters calculated based on linear Van’t Hoff plots showed the chiral separation was controlled by enthalpy. Better separation was not always at low temperature. The chiral recognition mechanisms were discussed. The elution orders of the eluting enantiomers were determined by a circular dichroism detector.

Development of a Bioaerosol single particle detector (BIO IN) for the Fast Ice Nucleus CHamber FINCH

Abstract. In this work we present the setup and first tests of our new BIO IN detector. This detector was constructed to classify atmospheric ice nuclei (IN) for their biological content. It is designed to be coupled to the Fast Ice Nucleus CHamber FINCH. If one particle acts as an ice nucleus, it will be at least partly covered with ice at the end of the development section of the FINCH chamber. The device combines an auto-fluorescence detector and a circular depolarization detector for simultaneous detection of biological material and discrimination between water droplets, ice crystals and non activated large aerosol particles. The excitation of biological material with UV light and analysis of auto-fluorescence is a common principle used for flow cytometry, fluorescence microscopy, spectroscopy and imaging. The detection of auto-fluorescence of airborne single particles demands some more experimental effort. However, expensive commercial sensors are available for special purposes, e.g. size distribution measurements. But these sensors will not fit the specifications needed for the FINCH IN counter (e.g. high sample flow of up 10 LPM). The newly developed -low cost- BIO IN sensor uses a single high-power UV LED for the electronic excitation instead of much more expensive UV lasers. Other key advantages of the new sensor are the low weight, compact size, and the little effect on the aerosol sample, which allows it to be coupled with other instruments for further analysis. The instrument will be flown on one of the first missions of the new German research aircraft "HALO" (High Altitude and LOng range).

Ultra fast electron beam X-ray computed tomography for two-phase flow measurement

Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies, we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focusing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm × 1.5 mm × 1.5 mm active pixel area. X-ray radiation is produced on a circular water cooled tungsten target. The CT system achieves up to 7000 frames per second with a spatial resolution of 1 mm. First two-phase flow experiments have been carried out on gas–water flows in bubble columns. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in future to study the evolution of two-phase gas–water pipe flow at high pressures and temperatures.

Integrated micromachined thermopile IR detectors with an XeF2 dry-etching process

Based on the Seebeck effect, the CMOS compatible micromachined thermopile is widely used in infrared detection for its advantages of low-cost, high batch yield, broad spectral response and insensitivity to ambient temperature. We present two integrated thermopile IR detectors on stacked dielectric layers realized by a standard P-well CMOS technology, followed by one CMOS compatible maskless XeF2 isotropic dry-etching step. Characterizations of CMOS devices, before and after XeF2 etching, respectively, were performed to investigate the effects of XeF2 etching on the CMOS devices. With a 2.5 µm thick stacked silicon oxide–nitride–oxide layer as an absorber, the rectangular thermopile detector and the circular thermopile detector provided responsivity of 14.14 and 10.26 V W−1, specific detectivity of 4.15 × 107 and 4.54 × 107 cm Hz1/2 W−1, and time constant of 23.7 and 14.6 ms, respectively. Compared with the rectangular thermopile detector, the circular thermopile detector is mechanically more stable, because its circular structure design eases the internal stress problem in the CMOS layers. After XeF2 etching, the maximum changes of threshold voltage, maximum transconductance and switching threshold voltage were 0.97%, 1.25% and 0.08%, respectively. Experimental results show that the effects of XeF2 etching on the CMOS devices are insignificant, and XeF2 etching is suitable for post-CMOS micromachining.

Flow imaging by high speed transmission tomography

Fourth generation medical X-ray scanners using a gantry with a rotating X-ray source and a fixed circular detector array as sensor head, are too slow for imaging of the process dynamics for instance in multiphase flows. To avoid inconsistent measurements and motion blurring, all measurements need to be carried out in a short time compared to the time constants of the process dynamics. Two different high speed tomographic imaging systems are presented here demonstrating that image rates of several thousand images per second is possible.

Stereoisomeric Separation and Bioassay of a New Organophosphorus Compound, O,S-Dimethyl-N-(2,2,2-trichloro-1-methoxyethyl)phosphoramidothioate: Some Implications for Chiral Switch

The manufacture and use of single- or enriched-enantiomer pesticides are green-chemistry developments advocated in the 21st century, but predictive work for chiral switch of newly produced chiral active ingredients is limited. In the present study, the stereoselective separation, target activity, and nontarget toxicity of O,S-dimethyl-N-(2,2,2-trichloro-1-methoxyethyl)phosphoramidothioate (MCP), a new organophosphorus compound, were investigated. Because being highly active and safe is a prerequisite for marketing single-isomer products, the above studies were used to offer some implications for the chiral switch of racemic MCP. The results showed that all four stereoisomers of MCP were successfully separated with a Chiralpak AD column on HPLC. The resolved isomers and the pairs of enantiomers were further distinguished using a circular dichroism detector, designating the first and third eluted peaks as one pair of enantiomers and the second and fourth peaks as the other pair. Then, the insecticidal activities and acute and delayed toxicities of the resolved isomers of MCP were evaluated by their acute lethal efficacy against Daphina magna , their inhibitory potentials to acetylcholinesterase (AChE), and axon-like outgrowth of the SH-SY5Y cells, respectively. The inhibition potencies of the isomers against AChE in SH-SY5Y cells were low and slightly stereoselective. On the other hand, a significant difference was observed among the isomers in their activities and delayed neurotoxicities. The 48 h acute toxicities of isomers to D. magna followed the order peak 1 approximately pair 1 (i.e., equimolar mixture of peaks 1 and 3) > peak 4 approximately racemate > pair 2 (i.e., equimolar mixture of peaks 2 and 4) > peak 2 > peak 3, with 1.0-6.3-fold differences among them. In comparison, the inhibitory potentials of the isomers toward axon growth of SH-SY5Y cells decreased in the order peak 2 > pair 2 > peak 4 > racemate > peak 3 > pair 1 approximately peak 1, with at least a 60-fold difference between the strongest and weakest inhibitors. Those results imply that peak 1 has the optimal target selectivity and ecological profile among the four stereoisomers. It was calculated that two-thirds of the usual pesticide usage can be saved concomitantly with a substantial decrease in neuropathic risk if MCP is present only as peak 1 rather than the racemate. When considering the absence of the economically feasible synthetic methods and techniques to produce optically pure isomers of organophosphorus pesticides, pair 1 of MCP shows considerable worth for future applications on the basis of its biological predominance and cost effectiveness.

Electroacoustic and Acoustic Attenuation Spectroscopy as New Tools for In Situ-Monitoring of Metal Oxide Precursor Preparation in Liquid Phase

The in situ-monitoring of a solid synthesis was realised by electroacoustic and acoustic attenuation spectroscopy. These techniques were applied to track the crystal growth of alumina precursor nanoparticles used as model compound. A commercially available set-up with a circular flow detector cell for joint electroacoustic and attenuation measurements was used. Course of zeta potential as well as particle growth was measured during continuous hydrolysis of dry Al-sec-butoxide in isopropanol. Zeta potential shows minima and maxima with increasing water amount, whereas particles start to grow significantly after a defined time of operation. In some experiments the synthesis was stopped ahead of time and the formed solids were additionally studied ex situ by characterisation methods such as solid-state NMR or transmission electron microscopy. Measured ultrasound data can be correlated to elemental processes during particle formation. First experiments on monitoring of synthesis scale-up show potential for future application of this technique.

A planar circular detector based on multiple point chemi- or bio-luminescent source within a coaxial cylindrical reactor

An analytical method was proposed for calculating radiative fluxes incident on a planar circular detector from a volume multiple point chemi- or bio-luminescent source inside a coaxial cylindrical reactor. The method was designed for a cylindrical reactor when the surface reflections were neglected and when chemi- or bio-luminescence reaches a detector embedded in the same homogeneous optical medium as the point emitters of the volume multiple point source model. The radiative fluxes from arbitrarily distributed point emitters were expressed by one generalized quadruple-integral formula. Then some double- and single-integral formulas were obtained for calculating radiative fluxes from identically radiating point emitters uniformly distributed within the reactor. Selected results were computed and illustrated graphically. The obtained formulas are suitable for optimizing and/or calibrating the considered source-detectors systems (optical radiometers or luminometers) and determining radiative fluxes generated by chemical, biological, and physical processes leading to chemi-, bio-, radio-, and sono-luminescence for example.

A local shift‐variant Fourier model and experimental validation of circular cone‐beam computed tomography artifacts

Large field of view cone-beam computed tomography (CBCT) is being achieved using circular source and detector trajectories. These circular trajectories are known to collect insufficient data for accurate image reconstruction. Although various descriptions of the missing information exist, the manifestation of this lack of data in reconstructed images is generally nonintuitive. One model predicts that the missing information corresponds to a shift-variant cone of missing frequency components. This description implies that artifacts depend on the imaging geometry, as well as the frequency content of the imaged object. In particular, objects with a large proportion of energy distributed over frequency bands that coincide with the missing cone will be most compromised. These predictions were experimentally verified by imaging small, localized objects (acrylic spheres, stacked disks) at varying positions in the object space and observing the frequency spectrums of the reconstructions. Measurements of the internal angle of the missing cone agreed well with theory, indicating a right circular cone for points on the rotation axis, and an oblique, circular cone elsewhere. In the former case, the largest internal angle with respect to the vertical axis corresponds to the (half) cone angle of the CBCT system (typically approximately 5 degrees - 7.5 degrees in IGRT). Object recovery was also found to be strongly dependent on the distribution of the object's frequency spectrum relative to the missing cone, as expected. The observed artifacts were also reproducible via removal of local frequency components, further supporting the theoretical model. Larger objects with differing internal structures (cellular polyurethane, solid acrylic) were also imaged and interpreted with respect to the previous results. Finally, small animal data obtained using a clinical CBCT scanner were observed for evidence of the missing cone. This study provides insight into the influence of incomplete data collection on the appearance of objects imaged in large field of view CBCT.

Performance tests of large area position-sensitive planar germanium detectors with conventional and amorphous contacts

Large area position-sensitive planar germanium wafers are increasingly being used for a variety of gamma-ray imaging and tracking tasks. Position sensitivity can be achieved through measuring charge collected on orthogonal strip electrodes, and by digital pulse shape analysis. However, the development of this detector technology has been slow, and criteria to measure improved performance have not been well established. We have studied 93 and 88 mm square segmented detectors of 20 mm thickness made with conventional boron and lithium electrodes, and two 100 mm circular segmented detectors of 14 mm thickness with amorphous germanium contacts. We have compared these detectors with a planar detector of 15 mm thickness. Conventional energy resolution tests of individual strips are insufficient to fully categorize the performance of the position sensitive detectors. We propose some basic tests which can rapidly quantify any segmented detector characteristics, and show potential inadequacies which become important when imaging or tracking is attempted.

Absolute Rotary Angular Measurement by Using Multi Electrode Circular Position Sensitive Detector

A new type of circular semiconductor position sensitive detector (PSD) called multi electrode circular PSD (ME-CPSD), which consists of a photosensitive region, a resister line, and 16 electrodes, is presented. The photosensitive region is in the shape of a ring, which is formed by the radial arrangement of long and narrow photodiodes. The outer ends of the photodiodes are connected to the continuous resistor line. Photoexcited carriers generated in the photodiode flow to the resistor line and are extracted by the multi electrode, which divides the resistor into 16 equal parts. The angular position of the light spot is calculated from the output current of the selected electrodes. Compared to conventional circular PSDs, the reliability of angular measurement is better, this is because the ME-CPSD does not have an undetectable region caused by unavoidable discontinuities in the structure of conventional circular PSDs. This device can not only measure the absolute angular position but also carry out a more precise angular measurement by selecting narrower electrode intervals. This device has the capability of realizing a high-precision noncontact angular measurement system with a simple construction.

The Chiral Separation of Triazole Pesticides Enantiomers by Amylose-tris(3,5-dimethylphenylcarbamate) Chiral Stationary Phase

The amylose-tris(3,5-dimethylphenylcarbamate) chiral stationary phase was synthesized and used to separate the enantiomers of triazole pesticides by high-performance liquid chromatography. The mobile phase was n-hexane-isopropanol applying a flow rate of 1.0 mL/min. Six triazole pesticides were enantioselectively separated. Myclobutanil, paclobutrazol, tebuconazole, and uniconazole obtained complete separation with the resolution factors of 5.73, 2.99, 1.72, and 2.07, respectively, and imazalil and diniconazole obtained partial separation with the resolution factors of 0.79 and 0.77 under the optimized conditions. The effect of the content of isopropanol as well as column temperature on the separation was investigated. A circular dichroism detector was used to identify the enantiomers and determine the elution orders. The results showed the low temperature was good for the chiral separation except for diniconazole. The thermodynamic parameters calculated based on linear Van't Hoff plots showed the chiral separations were controlled by enthalpy.

Quantitative Analysis of Three Chiral Pesticide Enantiomers by High-Performance Column Liquid Chromatography

Methods for the enantiomeric quantitative determination of 3 chiral pesticides, paclobutrazol, myclobutanil, and uniconazole, and their residues in soil and water are reported. An effective chiral high-performance liquid chromatographic (HPLC)-UV method using an amylose-tris(3,5-dimethylphenylcarbamate; AD) column was developed for resolving the enantiomers and quantitative determination. The enantiomers were identified by a circular dichroism detector. Validation involved complete resolution of each of the 2 enantiomers, plus determination of linearity, precision, and limit of detection (LOD). The pesticide enantiomers were isolated by solvent extraction from soil and C18 solid-phase extraction from water. The 2 enantiomers of the 3 pesticides could be completely separated on the AD column using n-hexane isopropanol mobile phase. The linearity and precision results indicated that the method was reliable for the quantitative analysis of the enantiomers. LODs were 0.025, 0.05, and 0.05 mg/kg for each enantiomer of paclobutrazol, myclobutanil, and uniconazole, respectively. Recovery and precision data showed that the pretreatment procedures were satisfactory for enantiomer extraction and cleanup. This method can be used for optical purity determination of technical material and analysis of environmental residues.

An ultra fast electron beam x-ray tomography scanner

This paper introduces the design of an ultra fast x-ray tomography scanner based on electron beam technology. The scanner has been developed for two-phase flow studies where frame rates of 1 kHz and higher are required. Its functional principle is similar to that of the electron beam x-ray CT scanners used in cardiac imaging. Thus, the scanner comprises an electron beam generator with a fast beam deflection unit, a semicircular x-ray production target made of tungsten alloy and a circular x-ray detector consisting of 240 CZT elements with 1.5 mm × 1.5 mm × 1.5 mm size each. The design is optimized with respect to ultra fast imaging of smaller flow vessels, such as pipes or laboratory-scale chemical reactors. In that way, the scanner is capable of scanning flow cross-sections at a speed of a few thousand frames per second which is sufficient to capture flows of a few meters per second velocity.

On-line Liquid Chromatography and Circular Dichroism Detection of Stereo-isomers of α-Tocopherol Derivatives Generated by an Electrochemical Reaction

The electrochemical oxidation of (+/-)-alpha-tocopherol on a porous graphite electrode was performed in the presence of methanol, and successive separation and detection of the products were performed by an on-line liquid chromatography/mass spectrometry system. Three products were identified, one of which was determined to be alpha-tocopheryl quinone, because its m/z was 469 [M+Na](+). The other two products showed identical mass and UV spectra, and were suspected to be diastereomers of 9-methoxy-alpha-tocopheron, because their molecular weights were m/z 483 [M+Na](+), and also because it is known that the chemical oxidation of alpha-tocopherol by benzoyl peroxide or N-bromosuccinimide in the presence of methanol should provide 9-methoxy-alpha-tocopheron. To confirm that these two compounds were diastereomers, a circular dichroism detector was used. The signs of both peaks detected by the circular dichroism detector at 230 nm were opposite. In addition to observations of identical mass and ultraviolet spectra, these results indicated that the two products were diastereomers of 9-methoxy-alpha-tocopheron, whose stereochemistry is different at the newly generated chiral center of the 9-position. The on-line use of a circular dichroism detector with an electrochemical cell/liquid chromatography system may expand the utility of the system to study the metabolism of a chiral drug.