A one-dimensional position-sensitive detector for thermal neutrons

A one-dimensional position-sensitive detector of thermal neutrons has been developed to equip high-efficiency neutron spectrometers at the ИБР-2 research reactor. The detector is based on a multiwire proportional chamber filled with a mixture of ³He + CF₄ and has an active area of 200 × 80 mm and a spatial resolution of 2 mm. The detector has been used to good effect in the REFLEX and HRFD spectrometers of the ИБР-2 reactor, as well as in the diffraction facility of the ИВВ-2M research reactor (Zarechnyi, Russia).     

A fiber-optic thermal detector of unconfined alpha particles

A prototype thermal detector intended for measuring spectra and profiles of energetic particles and based on a multifoil thermal detector was tested. Three types of absorbing films were tested: nickel foil, diamond-like carbon (DLC) film, and epitaxial CVD diamond film. A fiber-optic infrared bolometer was used as a sensing element.     

A thermal neutron detector based on single-crystalline silicon

It is shown that a change in the specific electrical conductivity (SEC) in silicon single crystals after irradiation and radiation defect annealing is directly proportional to the thermal neutron fluence. This fact is used as a basis of a method for measuring the neutron flux. In this case, the proportionality factor is dependent on the neutron spectrum, being independent of the initial SEC, which significantly simplifies detector calibration. In measurements of the thermal neutron fluence in terms of relative and absolute units, the rms was 4 and 8%, respectively.     

A scintillation strip detector for detection of thermal neutrons

A scintillation strip detector designed for precise experiments on the reflectometry of thermal neutrons is described. Test results obtained on the beam of a time-of-flight spectrometer have shown that the detector has a detection efficiency for thermal neutrons close to 100%, a lowered sensitivity to the neutron background, and a low level of intrinsic noise. The coordinate resolution of the detector can be varied in the range 1.5–0.1 mm. The strip is manufactured from a mixture of a ZnS(Ag) scintillator and a ⁶LiF neutron converter.     

GC-14A气相色谱仪热导检测器三种故障的处理方法

热导检测器 (ＴＣＤ)是ＧＣ - 14Ａ气相色谱仪常用检测器之一。但ＴＣＤ故障往往不易准确判断 ,处理不当还会扩大故障部位。本文在排除电路和气路方面的原因外 ,分析了ＴＣＤ常见的三种故障现象 ,提出了相应的处理方法。(1)开机后基线不稳 ,噪声大或基线严重漂移。故障分析 :可能是ＴＣＤ被污染 ,从ＴＣＤ工作时间长短可粗略推断ＴＣＤ受污染的程度。处理方法 :对于轻微污染 ,可将ＴＣＤ的气路进口和出口拆下 ,用 5 0ｍＬ注射器依次将丙酮、无水乙醇和蒸馏水从进气口反复注入 5～ 10次 ,用吹气球从进气口处缓慢吹气 ,吹出杂质和残余液体 ,然…     

Erosion, corrosion and erosion–corrosion of EB PVD thermal barrier coatings

Electron beam (EB) physical vapour deposited (PVD) thermal barrier coatings (TBCs) have been used in gas turbine engines for a number of years. The primary mode of failure is attributed to oxidation of the bond coat and growth of the thermally grown oxide (TGO), the alumina scale that forms on the bond coat and to which the ceramic top coat adheres. Once the TGO reaches a critical thickness, the TBC tends to spall and expose the underlying substrate to the hot gases. Erosion is commonly accepted as a secondary failure mechanism, which thins the TBC thus reducing its insulation capability and increasing the TGO growth rate. In severe conditions, erosion can completely remove the TBC over time, again resulting in the exposure of the substrate, typically Ni-based superalloys. Since engine efficiency is related to turbine entry temperature (TET), there is a constant driving force to increase this temperature. With this drive for higher TETs comes corrosion problems for the yttria stabilised zirconia (YSZ) ceramic topcoat. YSZ is susceptible to attack from molten calcium–magnesium–alumina–silicates (CMAS) which degrades the YSZ both chemically and micro-structurally. CMAS has a melting point of around 1240 °C and since it is common in atmospheric dust it is easily deposited onto gas turbine blades. If the CMAS then melts and penetrates into the ceramic, the life of the TBC can be significantly reduced. This paper discusses the various failure mechanisms associated with the erosion, corrosion and erosion–corrosion of EB PVD TBCs. The concept of a dimensionless ratio D/d, where D is the contact footprint diameter and d is the column diameter, as a means of determining the erosion mechanism is introduced and discussed for EB PVD TBCs.     

On the analysis of in-tube flaw-detection results characterizing the state of a trunk gas pipeline with corrosion flaws

Today, results of in-tube flaw detection (ITFD) are used mainly to solve routine problems of the provision of service reliability of operating gas pipelines (via the removal or selective repair of damaged pipes). However, the task of nondestructive testing consists in not only the detection of flaws but also in the determination of the principal causes of their appearance. This calls for the use of quantitative indexes of flaw parameters for estimating steady tendencies toward the development of damaging, determining the most essential causes of the formation of detected flaws, and predicting possible dynamics of their propagation as the time of operation of a trunk gas pipeline (TGP) system increases. These tasks can be solved based on an analysis of primary results of ITFD by selecting and using steady quantitative indexes of the total damaging using statistical techniques.Translated from Defektoskopiya, Vol. 40, No. 10, 2004, pp. 79–88.Original Russian Text Copyright © 2004 by Gorchakov, Dolgov, Yu. Surkov, Rybalko, A. Surkov.     

单片机控制的气相色谱热导检测器研究

针对气相色谱热导检测器的弱信号失真问题,研究与设计热导检测器的弱信号测量电路及其单片机控制系统,进一步提高气相色谱热导检测系统的灵敏度和可靠性。     

An LED-based illuminator for microphotometric studies of cells

A fiber-optic illuminator with superbright semiconductor LEDs for single-cell microphotometry is described. The illuminator provides excitation at wavelengths of 385, 440, 480, and 530 nm (30, 70, 50, and 20 mW, respectively). The long-term instability of its radiant power is ≤0.1 %/h, and its service life is 30000 h. The characteristics of the LED-based illuminator are compared to those of a commercial illuminator based on a DeltaRAM scanning monochromator (Photon Technology International, United States).     

A microcantilever-based pathogen detector

The ability to detect small amounts of materials, especially bacterial organisms, is important for medical diagnostics and national security issues. Engineered micromechanical systems provide one approach for constructing multifunctional, highly sensitive, real-time, immunospecific biological detectors. We present qualitative detection of specific Salmonella enterica strains using a functionalized silicon nitride microcantilever. Detection is achieved due to a change in the surface stress on the cantilever surface in situ upon binding of a small number of bacteria. Scanning electron micrographs indicate that less than 25 adsorbed bacteria are required for detection.     

A multielectrode X-ray detector

A multielectrode vacuum photoemission detector for X-ray tomography of plasmas at the ITER facility is described. The detector characteristics have been investigated with an X-ray source. The spectral response of the detector to X-ray photons with energies of 3–30 keV has been determined. The spatial and angular dependences of the X-ray detection efficiency are presented. The useful signal of the ITER facility has been estimated.     

基于LED的光谱可调光源结构研究

介绍了一个由大量LED组合而成的光谱可调光源,通过不同LED的组合产生不同光谱分布,可以模拟各种光源。该光源主要由LED屏体、光谱匹配模块以及LED控制驱动模块构成。LED屏体由2 304个窄带LED组成,通过LED数据分配卡将接收到的显示数据进行分配,并驱动屏体上的LED,以PWM的方式精确控制每一个LED的电流,实现256级及以上灰度等级显示。整个系统经初步调试,已能模拟部分光谱。该光源将具有广泛的应用前景。     

Development of a thermal neutron detector based on scintillating fibers and silicon photomultipliers

We propose a technique for thermal neutron detection, based on a (6)Li converter placed in front of scintillating fibers readout by means of silicon photomultipliers. Such a technique allows building cheap and compact detectors and dosimeters, thus possibly opening new perspectives in terms of granular monitoring of neutron fluxes as well as space-resolved neutron detection.     

新型三电炉结构平板式导热系数测定仪的设计

为实现导热系数的快速测定,基于一维无限大稳态导热原理,研制了一种新型三电炉结构平板式导热系数测定仪。它以MSP430F147单片机为测量控制核心,设计了相应的接口电路。相对于同类产品,在减少体积、减少测试过程中试件数量及利用PID温度控制等方面进行了良好的设计。实验结果表明,该仪器具有测试速度快、误差小、量程宽和造价低等特点。     

气相色谱热导检测器的信号测量与电源电路研究

在气相色谱仪中,采用热导检测器检测物质成分的浓度变化,具有构造简单、测定范围广、稳定性好、线性范围宽等优点。针对气相色谱热导检测器的弱信号失真和电源不稳定问题,研究与设计热导检测器的弱信号测量电路、信号放大电路以及电源电路。实践表明,该方法有效提高气相色谱热导检测系统的可靠性。     

A neural-network classifier of flaws for multifrequency Eddy-current tests of heat-exchange pipes

A neural-network classifier has been developed that evaluates the geometric characteristics of a detected flaw on the basis of the parameters of the corresponding multifrequency signals obtained via scheduled eddy-current tests conducted with a through-type probe. The classifier is intended for testing heat-exchange pipes in steam generators of a nuclear power plant with a water-moderated water-cooled power reactor. The representative library of signals required for the design was formed on the basis of theoretical and experimental data. The theoretical data were obtained in a numerical physical and mathematical model of the electromagnetic testing procedure implemented with the MagNum3D program for finite-element analysis. The experimental data were obtained through measurement of multifrequency eddy-current signals from test specimens with artificial flaws.     

A three-parameter model for fatigue behaviour of circumferential surface flaws in pipes

A three-parameter model, recently proposed by the authors for part-through-cracked round bars, is employed herein to examine the shape evolution of a circumferential external surface defect in a metallic round pipe under fatigue loading. The elliptical-arc flaw presents an aspect ratio α=a_el/b_el (a_el,b_el=ellipse semi-axes) and a relative crack depth ξ=a/t, where a and t are the depth of the deepest point on the crack front and the pipe wall thickness, respectively. The third parameter of the model is the ellipse shifting s=a_el/a, which defines the distance of the ellipse centre from the external boundary of the pipe cross-section. Thick- and thin-walled pipes are considered. Fatigue crack propagation paths in the diagram of α against s and ξ are numerically obtained for different initial flaw configurations under cyclic bending loading.     

A new method for detection of internal flaws in ferrodielectrics and ferroelectrics

A fundamentally new method for detection of internal flaws in ferrodielectrics and ferroelectrics is substantiated theoretically and experimentally. Traditional acoustic methods are based on the flaw-surface reflection of acoustic waves that occurs owing to abrupt changes in elastic properties at an interface. In contrast, the generation of acoustic waves that occurs upon incidence of EM waves on the flaw surface and that results from abrupt changes in the magnetoelastic and piezoelectric properties forms the basis of the new method.     

A nonlinear modulation technique used to inspect flaws: Electromagnet-caused modulation

Different mechanisms of local modulation of acoustic characteristics of model flaws (crack, notch) caused by a U-type electromagnet are considered with reference to a nonlinear modulation acoustic technique of crack detection. The results of an experiment on notch modulation performed by means of bending an object’s surface and applying a magnetic field and tangential forces to the surface near the foot of an electromagnet, depending on the electromagnet orientation with respect to the notch plane and amplitude of its excitation, are discussed. The specific features of two-dimensional detection of individual cracks (closed and half-open) in metal plates by linear and nonlinear techniques are discussed.     

A measuring square-law diode detector

A general approach, circuit diagrams, and test results of a square-law detector with improved metrological characteristics are presented. The detector is based on a “diode + current-to-voltage converter” scheme. The measured characteristics are as follows: the dynamic range is 40 dB, and quadraticity factor is 2.00 ± 0.05. The working frequency band of a particular detector is from 0.001 to 2 GHz. The proposed approach is suitable for detectors of most kinds (series, parallel, single- and two-cycle, etc.), operating in the radio frequency band.