An Apparatus for β–γ Ray Separation

Abstract

A set‐up based on a coincidence measurement was developed in order to separate beta and gamma rays emitted from a ¹³⁷Cs sample. The coincidence system is composed of a NaI(Tl) and a plastic scintillation detector. According to the experimental results, a clear separation between beta and gamma rays was achieved.     

Silicon nitride windows for electron microscopy of whole cells

Silicon microchips with thin, electron transparent silicon nitride windows provide a sample support that accommodates both light‐, and electron microscopy of whole eukaryotic cells in vacuum or liquid, with minimum sample preparation steps. The windows are robust enough that cellular samples can be cultured directly onto them, with no addition of a supporting film, and there is no need to embed or section the sample, as is typically required in electron microscopy. By combining two microchips, a microfluidic chamber can be constructed for the imaging of samples in liquid in the electron microscope. We provide microchip design specifications, a fabrication outline, instructions on how to prepare the microchips for biological samples, and examples of images obtained using different light and electron microscopy modalities. The use of these microchips is particularly advantageous for correlative light and electron microscopy.     

High-resolution backscatter electron imaging of colloidal gold in LVSEM

High‐resolution backscatter electron (BSE) imaging of colloidal gold can be accomplished at low voltage using in‐lens or below‐the‐lens FESEMs equipped with either Autrata‐modified yttrium aluminium garnet (YAG) scintillators doped with cerium, or with BSE to secondary electron (SE) conversion plates. The threshold for BSE detection of colloidal gold was 1.8 keV for the YAG detector, and the BSE/SE conversion was sensitive down to 1 keV. Gold particles (6, 12 and 18 nm) have an atomic number of 79 and were clearly distinguished at 500 000× by materials contrast and easily discriminated from cell surfaces coated with platinum with an atomic number of 78. BSE imaging was relatively insensitive to charging, and build up of carbon contamination on the specimen was transparent to the higher energy BSE.     

Detective quantum efficiency of electron area detectors in electron microscopy

Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.     

Measurements of tribological properties of poly(pyrrole) thin film bearings

We report the results of a recent study on the tribological properties of electropolymerised thin films at light loads and low speeds. Poly(pyrrole) films incorporating different counter-ions have been electrochemically deposited onto gold electrodes on the plano-convex glass substrates and studied extensively. The measuring apparatus has been greatly improved from that reported earlier and now provides simultaneous monitoring of frictional force and wear. High precision capacitive gauging is employed to provide high resolutions of frictional force of better than 100 μN and height variation (wear) of 2 nm. A large number of specimens of poly(pyrrole) grown from five different counter-ions were prepared and their performances evaluated. The film morphology of each type of film was examined by atomic force microscopy (AFM) for control of the variability of film formation. Results are presented for the friction coefficients and wear rates observed for the films typically at a load of 2 N and a sliding speed of 5 mm s⁻¹. The effects of normal loading force and sliding speed on the friction coefficient are also discussed with a load range of 0.2–5 N and a sliding speed up to 30 mm s⁻¹.     

纳秒激光等离子体光源的光谱测量技术

提出了一种新的探测和测量激光等离子体软X射线源光谱强度的方法。此方法使用通道电子倍增器和定标过的硅光电二极管为探测器,前者是非标准探测器,后者为标准探测器。应用电荷灵敏前置放大器和峰值探测器测量探测器产生的电量,并以高分辨率的光谱仪为分光元件,在已知光栅效率、通道电子倍增器增益、硅光电二极管能量响应的条件下,给出了计算激光等离子体软X射线源在某一波长光谱强度的公式。     

Efficiency Determination for NaI (Tl) Detectors in the 23 keV to 1333 keV Energy Range

Abstract

The photopeak efficiency of a NaI (Tl) detector was determined experimentally for 23‐1333 keV photon energy by using polyester coated radioisotopes ²²Na, ⁵⁴Mn, ⁵⁷Co, ⁶⁰Co, ¹⁰⁹Cd, ¹³⁷Cs, and ¹³³Ba. The energy resolution of the NaI (Tl) detector was also measured. The data were analyzed using the Genie‐2000 from Canberra. The experimental values were fitted to an analytical function of photon energy and an agreement was observed for the entire range of the studied energies. The results have shown that the NaI (Tl) detector is a particularly attractive detector for field application, as it works at room temperature and has a high probability of detecting gamma radiation.     

A novel pixellated solid‐state photon detector for enhancing the everhart–thornley detector

This article presents a pixellated solid‐state photon detector designed specifically to improve certain aspects of the existing Everhart–Thornley detector. The photon detector was constructed and fabricated in an Austriamicrosystems 0.35 µm complementary metal‐oxide‐semiconductor process technology. This integrated circuit consists of an array of high‐responsivity photodiodes coupled to corresponding low‐noise transimpedance amplifiers, a selector‐combiner circuit and a variable‐gain postamplifier. Simulated and experimental results show that the photon detector can achieve a maximum transimpedance gain of 170 dBΩ and minimum bandwidth of 3.6 MHz. It is able to detect signals with optical power as low as 10 nW and produces a minimum signal‐to‐noise ratio (SNR) of 24 dB regardless of gain configuration. The detector has been proven to be able to effectively select and combine signals from different pixels. The key advantages of this detector are smaller dimensions, higher cost effectiveness, lower voltage and power requirements and better integration. The photon detector supports pixel‐selection configurability which may improve overall SNR and also potentially generate images for different analyses. This work has contributed to the future research of system‐level integration of a pixellated solid‐state detector for secondary electron detection in the scanning electron microscope. Microsc. Res. Tech. 76:648–652, 2013. © 2013 Wiley Periodicals, Inc.     

一种新型的微化学分析器

一种新型的微化学分析器,单片集成毛细管区带电泳系统的制作 及其分离性质。在玻璃片上的实验模型中,分离沟道长４．５ｃｍ在１００Ｖ／ｃｍ的电下理论塔板数可至４０,０００。     

Application of channel electron multipliers in an electron detector for low‐voltage scanning electron microscopy

An electron detector containing channel electron multipliers was built and tested in the range of low‐voltage scanning electron microscopy as a detector of topographic contrast. The detector can detect backscattered electrons or the sum of backscattered electrons and secondary electrons, with different amount of secondary electrons. As a backscattered electron detector it collects backscattered electrons emitted in a specific range of take‐off angles and in a large range of azimuth angles enabling to obtain large solid collection angle and high collection efficiency. Two arrangements with different channel electron multipliers were studied theoretically with the use of the Monte Carlo method and one of them was built and tested experimentally. To shorten breaks in operation, a vacuum box preventing channel electron multipliers from an exposure to air during specimen exchanges was built and placed in the microscope chamber. The box is opened during microscope observations and is moved to the side of the scanning electron microscope chamber and closed during air admission and evacuation cycles enabling storing channel electron multipliers under vacuum for the whole time. Experimental tests of the detector included assessment of the type of detected electrons (secondary or backscattered), checking the tilt contrast, imaging the spatial collection efficiency, measuring the noise coefficient and recording images of different specimens.     

Slow-neutron detector based on thin CVD diamond film

A slow-neutron detector based on thin CVD diamond film is discussed. A deep graphitized layer in the diamond film acts as one of the electrodes in the detector. The detector demonstrates low sensitivity to γ radiation, at the background level. The detector is tested with a laboratory neutron source based on the isotope ²⁵²Cf in a moderator. Slow neutrons are detected by means of the boron isotope ¹⁰В and lithium isotope ⁶Li. In both cases, slow neutrons are recorded with about 3% efficiency. The efficiency of slow-neutron recording is also assessed theoretically.     

高功率发光二极管诱导荧光微流控芯片分析小型化检测器的研制

以高功率发光二极管（LED）为激发光源,研制了一种新型的小型化LED诱导荧光检测器,用于微流控芯片分析检测。利用MOS管的压控恒流原理,设计恒流驱动电路,使高功率LED发光稳定。通过设计和制造光学结构,成功将LED的发散光聚焦成约3.5mm×0.3mm的线状光束,可方便地与微流控芯片中的微通道对准,避免了复杂的机械校准结构。光学系统体积大大减少,约为9.5cm×4cm×17cm。用荧光染料NBD和高密度脂蛋白评价该体系的性能,结果表明LED激发光源稳定,检测器重复性好;样品峰形良好,可用于微芯片毛细管电泳分析检测。基本实现了LED诱导荧光检测器的微型化。     

A multichannel wire gas electron multiplier

A novel and relatively simple method of production of electrodes for a multichannel wire gas multiplier was developed. Two modifications of the multipliers have been tested: with a multiplication of electrons between two wire electrodes, MWGEM, and between a wire electrode and continuous anode, MWCAT. For both MWGEM and MWCAT detectors, filled with neon under pressure of 760 Torr and irradiated by β-particles (⁶³Ni), the coefficient of proportional multiplication of electrons up to ～10⁴ was obtained. For the MWGEM detector irradiated by α-particles (²³⁹Pu), the coefficient of proportional multiplication of 300 was obtained. It is observed, that in contrast to the GEM detectors, produced by perforation of a metal-clad plastic foil, in a MWGEM the discharges do not destroy its electrodes even for the potentials above the threshold of discharges. The results on operation of the MWCAT filled with Ar, Ar + 20% CH₄, and Ar + 1% Xe are also presented.     

太赫兹CMOS场效应管模型及实验分析

针对商业CMOS(互补金属氧化物半导体)场效应管模型在高频下易失效的问题,运用ADS软件构建了基于经典动力学理论的非线性RCL传输线模型,并结合实测数据说明了本文模型的精准性及太赫兹波段场效应管的工作原理。构建了基于经典动力学理论的非线性RCL传输线模型仿真系统,并将其与商业模型仿真结果进行对比,分析了在太赫兹波段本文模型与商业模型的区别。测试了现有场效应管探测器的频率响应,并对实测数据与两种模型仿真数据进行对比,说明本文模型提高了预测精度。最后,结合3σ原则分析了场效应管沟道尺寸对载流子散射效应的影响,以及场效应管进入弹道工作模式的条件。实验结果表明:本文模型与商业模型的区别主要在于模型中是否存在电感部分,该部分可作为场效应管沟道中载流子动量是否守恒及散射效应是否可以忽略的表征参数。相较于商业模型,本文模型对探测器最佳频率工作点的预测精准度可提高0.3%,对探测器带宽的预测精准度可提高约10%。该项研究为CMOS场效应管模型的精确建立及仿真分析提供了良好基础。     

Evaluation of Halogen‐Specific Detector (XSDTM) for Trace Analysis of Chlorinated Fatty Acids in Fish

Abstract

The applicability of a halogen‐specific detector (XSD?, manufactured by OI Analytical) was evaluated for GC analysis of chlorinated fatty acid methyl esters (FAMEs) that are present at trace levels in transesterified fish extract, a complex matrix consisting of similar but nonchlorinated compounds. A characteristic of the XSD working principle is that thermal electron emission, negative surface ionization and positive surface ionization are all operative in a concerted manner. While the XSD is not superior to other GC detectors in terms of signal‐to‐noise, its merit is in its high selectivity (10⁶) and low detection limit (2 pg Cl) for chlorinated fatty acids, and ease of operation and maintenance. Its reasonably wide linear range (up to 10 ng Cl) is desirable for trace analysis of chlorinated FAMEs. A major drawback of this detector is a certain degree of peak broadening and peak tailing of eluted compounds with concentrations larger than ～1 ng Cl/µL in the injected solution even though this value does not exceed the upper limit of the XSD linear range. Nevertheless, in trace analysis of chlorinated compounds, the concentrations of analytes are usually well below 1 ng Cl/µL. Parallel use of the XSD and a universal detector such as FID in gas chromatography is useful for optimizing operation conditions for trace analysis and simultaneously analyzing nonchlorinated major components.     

高效毛细管电泳仪的研制

介绍了国内最早出现的高效毛细管电泳商品化仪器———１２２９型高效毛细管电泳仪。简要说明了１２２９型高效毛细管电泳仪的原理、结构、特点和设计依据，它采用了两种进样方式、多波长紫外在线检测系统、弹簧压力冲洗方式、恒温及数据处理系统。给出了分离前列腺素和血栓素的实验条件和图谱。     

Design and operation of a portable scanner for high performance microchip capillary array electrophoresis

We have developed a compact, laser-induced fluorescence detection scanner, the multichannel capillary array electrophoresis portable scanner (McCAEPs) as a platform for electrophoretic detection and control of high-throughput, integrated microfluidic devices for genetic and other analyses. The instrument contains a confocal optical system with a rotary objective for detecting four different fluorescence signals, a pneumatic system consisting of two pressure/vacuum pumps and 28 individual addressable solenoid valves for control of on-chip microvalves and micropumps, four Polymerase Chain Reaction (PCR) temperature control systems, and four high voltage power supplies for electrophoresis. The detection limit of the instrument is ~20 pM for on-chip capillary electrophoresis of fluorescein dyes. To demonstrate the system performance for forensic short tandem repeat (STR) analysis, two experiments were conducted: (i) electrophoretic separation and detection of STR samples on a 96-lane microfabricated capillary array electrophoresis microchip. Fully resolved PowerPlex(?) 16 STR profiles amplified from 1 ng of 9947A female standard DNA were successfully obtained; (ii) nine-plex STR amplification, sample injection, separation, and fluorescence detection of 100-copy 9948 male standard DNA in a single integrated PCR- capillary electrophoresis microchip. These results demonstrate that the McCAEPs can be used as a versatile control and detection instrument that operates integrated microfluidic devices for high-performance forensic human identification.     

Performance Analysis of Wire Electrodes on Machining Ti-6Al-4V Alloy using Electrical Discharge Machining Process

High-strength materials with complex shapes can be easily machined by electrical discharge machining process. In the present study, an attempt has been made to analyze the influence of wire electrode on Kerf width and workpiece surface roughness in wire EDM process. Due to its importance in the aircrafts and automobiles, Ti-6Al-4V alloy has been chosen as the workpiece material. The various experiments have been conducted based on a Taguchi L₉ orthogonal array with various types of wire electrodes, such as conventional brass wire, zinc-coated wire and diffused coated brass wire. From the experimental results, it has been observed that diffused coated wire produced better surface finish with minimum kerf width compared to the other two wire electrodes. It has also been observed that the pulse off-time has more influent nature on machining characteristics such as surface roughness and kerf width.     

A Versatile Thin-Layer Detector Cell for High Performance Liquid Chromatography

ABSTRACT

A thin-layer electrochemical cell constructed from engineering plastics is described. The sandwich design can accommodate carbon or metal electrodes embedded in the wall of a rectangular channel. Miniature grid electrodes can be placed across the channel. The new transducer has been used in both static and hydrodynamic experiments including amperometric detection in liquid chromatography.     

Reversed‐Phase Liquid Chromatography with Electrokinetic Flow Analysis System

Abstract

An electrokinetic flow analysis system was introduced for reversed‐phase chromatography separation. It consisted of a C₈‐modified silica monolithic column, a UV‐Vis detector, and a pressurizing electroosmosis pump (EOP) to deliver mobile phase steadily and continuously. Acetonitrile was used as the organic solvent component of the mobile phase, i.e., the pump carrier, to improve the separation resolution of three aromatic compounds. The effect of acetonitrile concentration on the separation resolution and flow rate of mobile phase was investigated. When 35% acetonitrile (v/v) solution, containing 0.5 mmol/L hexamethylene tetraamine, was used as the mobile phase, three aromatic components could be baseline separated by the electrokinetic flow analysis system.