骨铅体内测量系统最佳测量位置的选择

^109Cd K XRF骨铅体内测量系统对体重指数大的对象测量所得的结果误差较大。测量时胫骨在探测器前的位置对测量结果误差的影响很大。采用模拟重指数大的被测对象的大体模,与原来的标准体模在探测器前不同距离时进行测量的对比分析表明,体重指数大的被测对象因其胫骨周围组织层较厚,造成康普顿计数大量增加。若胫骨与探测器的距离太近,仪器不能正常工作,致使X能谱图谱形畸变,得到不正确的结果。因此,在测量时,应保持胫骨在探测器前的距离为25mm,同时,应注意相干散射峰的峰位变化,保持仪器即时显示的死时间30%左右,以保证最后测量结果的精密度和准确度。     

Evaluation of direct axial sample introduction for ion mobility detection after capillary gas chromatography

An ion mobility detector has been designed and constructed for direct axial interfacing with capillary gas chromatography. The principle advantages of this detector were the following: (1) Direct concentric introduction of the capillary column into the ionization region, eliminating peak broadening in the transfer line and improving the efficiency with which neutral molecules were swept from the detector. (2) A variable capillary insertion distance, providing a sensitivity/resolution interplay that could be modified in response to the needs of the assay. (3) An inert gas flow external to the drift cylinder, preventing atmospheric impurities from infiltrating the ultratrace detector. Qualitative and quantitative capabilities of the detector were evaluated using standard preparations of n-hexyl ether.     

Use of the Pearson IV function to describe the dependence of detection efficiency of Ge detectors on gamma-ray energy

2000 analytical functions were fitted to the measured gamma-ray detection efficiencies of a Ge detector for a small irradiation vial located at the closest distance from the detector. Among these, the Pearson IV function, gave the best fit. The measured and calculated efficiencies were compared for 50 determinations (for energies which varied between 61 and 2754 keV) and a relative standard deviation of 8.3% was obtained.     

Effect of different arrangements of point source,aluminum absorber and detector on mass absorption coefficient of beta-particles

Summary The transmission of 0.766 MeV beta-particles emitted from ²⁰⁴Tl through aluminum has been investigated for different arrangements of point source, absorber and detector. In the first arrangement, the mass absorption coefficient (μ_m) has been measured as a function of the absorber to the source distance (H_AS), when the absorber foil was placed just above the window of a surface barrier solid state detector. In the second arrangement, the mass absorption coefficient has been measured as a function of the absorber to detector distance (H_AD), when the absorber foil was placed just on the source. The measured mass absorption coefficients of beta-particles have been compared to the values gained in a previous work.     

An X-ray fluorescence spectrometer with a pyroelectric X-ray generator and a secondary target for the determination of Cr in steel

An X-ray fluorescence (XRF) setup with a pyroelectric X-ray generator and a secondary target for the determination of Cr in steel is presented. The pyroelectric X-ray generator, which can be driven by a dry battery, is a low power X-ray source and emits X-rays over a large solid angle. X-rays emitted by this generator can be effectively put to use by a disk-shaped secondary target. An appropriate arrangement of (i) X-ray generator, (ii) sample support, (iii) secondary target, and (iv) detector enables secondary X-rays to irradiate the sample from a short distance. The secondary X-rays are emitted from a wide-area secondary target. The present arrangement also enables the sample to be placed near the detector. The short distance from the sample to both the secondary target and the detector enhances signal intensity. An absolute amount of 1.3 μg Cr can be detected by the present setup. A minimum detection limit of 0.09 wt.% Cr in steel by 1000-s measurement has been achieved.     

Semi-empirical determination of detector absolute efficiency in INAA of voluminous samples

When neutron activation analysis of voluminous samples is performed using the absolute method, the detector absolute efficiency for -ray emiting distributed sources must be known. In this study, a Monte-Carlo program was developed to include the calculation of the effective solid angle subtended by a collimated detector from irregularly shaped voluminous samples. The program cna cope with dififerent sample shapes and geometries provided that the sample covers the view of the detector. Data such as the source and detector dimensions, the source-detector distance, the detector view at a cartain distance, the thickness and the composition of any intervening materials, the -ray energies of interest and the corresponding attenuation coefficients for each material are required. The method adopted for calculating the detector absolute efficiency of the voluminous sample in a certain geometry takes into account the effect by -rays baing emited from different position within the sample and also considers their attenuation in the sample material as well as any intervening materials between the sample and the detector and is compared with a reference point source. The alculations are varified experimentally using a distributed source of 75 mm diameter and 100 mm thickness and two semiconductor detectors. The difference between the calculated and measured absolute efficiencies did not exceed 4%.     

A computer program for calculating Ge(Li) detector counting efficiencies for Marinelli beakers

A novel computing method has been developed to calculate the absolute photopeak efficiency of a Ge(Li) detector for Marinelli beakers of different heights and diameters and with variable density. For each point in the cylindrical sample the detection efficiency is calculated taking into account the distance from the detector and gamma-ray attenuation and the efficiency is integrated numerically over the volume of the sample. The detector is approximated as a point detector with an experimentally determined effective interaction depth. It is necessary to measure the absolute efficiency for a point source located on the detector axis and on a line beside the detector parallel to the axis. The computer program calculates the absolute counting efficiency for Marinelli beakers of any geometry and for any density. The measured and calculated values for three different densities give a good (–2.2%) overall agreement.     

The Measurement of Extremely Low Light Levels in Analytical Chemi- and Bio-Luminescence: A Mathematical and Practical Evaluation of Some Physical Factors Influencing Detector Output and Instrument Design

Abstract

In order to study the design features which affect the sensitivity of chemi- and bio-luminescence measuring devices, mathematical models have been devised. These models have been tested experimentally, and good agreement with their predictions obtained. Features such as dimensions of source and detector, distance from source to detector, and the use of mirrors have been investigated. This approach has provided a rational basis for the design of luminescence measuring devices.     

高效毛细管电泳紫外检测器光路的特殊性及其优化

紫外检测器用于高效毛细管电泳（ＨＰＣＥ）的主要难题在光路中,ＨＰＣＥ中熔融石英毛细管（内径通常在５０μｍ左右）直接放在光路中,一方面光程短,另一方面,光在透镜及毛细管界面上的折射与反射使光程常比毛细管内径短,甚至可能绕过毛细管内腔［１,２］．本文编制...     

An empirical expression for the full energy peak efficiency of an N-type high purity germanium detector

An empirical expression for the full energy peak efficiency (ε) in terms of the gamma-ray energy (E) and the vertical distance from the detector surface (z) (i.e.,ε=ε(z,E)) has been obtained for an N-type high purity germanium (HPGE) detector using an extended mixed standard radionuclide solution. Comparison of the calculated efficiencies and the experimentally measured values for the energy range of 59.5–1332.5 keV and a source-to-detector distance of 1.2–7.2 cm showed that the theoretical values agree with that of the experiment within 1.5–3.7% standard deviations. This shows a good agreement between the theory and the experiment.     

Quantitative measurement of 125I with NaI(Tl) scintillation survey meter

This paper describes a NaI(Tl) scintillation survey meter which can quantify 125I on a contaminated surface in situ. This survey meter has four inherent windows; 20-45 keV the singles photopeak region, 45-80 keV the sum photopeak region, 20-80 keV the total photopeak region, and 80 keV-. The activity was calculated based on the sum peak method. The calculated activity of a point source agreed with the standardized source activity within an uncertainty of about 10% both up to the distance of 3 cm from the detector surface along the axis of the detector and on the detector surface. The activity of a simulated plate source also agreed with the source activity within the same uncertainty.     

Instrument-induced effects in the analysis of polycyclic aromatic compounds by capillary gas chromatography with atomic emission detection (GC-AED)

Peak splitting of high molecular weight polycyclic aromatic compounds originating from the microwave plasma of an atomic emission detector (AED) coupled to a GC has been described and evaluated. The influence of the solute structure, solute concentration, and physical conditions in the AED (such as detector temperature, make-up gas flow, concentration of reagent gases and distance of column end from the plasma) have been studied. An explanation is presented for peak splitting, which is based on an insufficient solute decomposition and solute mass flow in the discharge tube. Modification of the instrument by introduction of additional make-up gas applied through the transfer line has been shown to improve peak shape and solute response.     

Geometrical counting efficiency for a circular radiating source and a circular detector using a microcomputer simulation

For versatile applications of alpha-spectrometric analysis, the geometrical counting efficiency was conveniently evaluated for a circular detector faced to a circular radiating source with a Monte Carlo simulation method using a microcomputer after checking the qualities of the random numbers. The results were tabulated as functions of the distance (Q) between the detector and the source and of the source diameter (P), normalized with the detector diameter. An application was attempted for the uniformity examination of a natural uranium source electrodeposited on a stainless steel plate.     

Influence of the distance between a spectrometer and sample on the intensity of X-ray fluorescence

Expressions for calculating the extreme point coordinates of focal spots of X-ray tubes and a detector’s sensitive area are found. These coordinates are used in calculations of the sample area. The dependence of the X-ray fluorescence intensity on the distance between a spectrometer and an analyzed sample is studied experimentally. The intensities of the FeK _α spectral lines in iron-containing materials are calculated at different geometric parameters of a spectrometer. It is found that the distance between a sample and detector at which the maximum of the measured intensity is observed depends on the size and position of the detector and X-ray tube collimators, as well as on the relative position of the X-ray tube and detector. Recommendations on how to achieve the maximum intensity of X-ray fluorescence are proposed. The results of the present work can be used for the development of X-ray fluorescence analysis techniques applicable for free-flowing materials directly in technological processes.     

Raman efficiencies of natural rocks and minerals: performance of a remote Raman system for planetary exploration at a distance of 10 meters

Raman spectroscopy is a powerful technique for materials analysis, and we are developing and analyzing a remote Raman system for use on a planetary lander or rover. We have acquired data at a distance of 10m from a variety of geologic materials using different instrument designs. We have employed a pulsed laser with both an ungated detector and a gated detector. A gated detector can reduce long-lived fluorescence while still collecting all Raman signal. In order to design a flight instrument, we need to quantify how natural surfaces will respond to laser stimulus. We define remote Raman efficiency of natural surfaces as the ratio of radiant exitance leaving a natural surface to the irradiance of the incident laser. The radiant exitance of a natural surface is the product of the sample radiance, the projected solid angle, and the full-width-half-maximum of the Raman signal. We have determined the remote Raman efficiency for a variety of rocks and minerals. The best efficiencies are achieved for large, clear, single crystals that produce the most radiant exitance, while darker fine-grained mineral mixtures produce lower efficiencies. By implementing a pulsed laser, gated detector system we have improved the signal detection and have generally decreased the integration time necessary to detect Raman signal from natural surfaces.     

Characteristics of NaI detector in positron imaging device HEADTOME employing circular ring array

In positron emission computed tomographs employing circular ring arrays of detectors, the performance of the imaging device has been specified ultimately by the characteristics of the detector. The responses of NaI detector were studied when detecting positron annihilation photon (511 keV). The study was mainly by using the NaI detector used in hybrid emission computed tomography (CT) "HEADTOME" we had developed. A series of measurements were carried out positioning two detectors with 40 cm distance and scanning 22Na point source in water. Both detectors was inclined from 0 degrees through 30 degrees to change incident angle of positron annihilation toward crystal face. Energy window was set from 100 to 700 keV. The results were presented as follows: Shortening the crystal length from 7 to 5 cm made sensitivity decrease about 10% and resolution deteriorate about 1 mm (FWHM). As the results of varying the width of the crystal, 20 mm width was optimal at any incident angle. The lead septum between the detectors was the thickness of 4 mm enough to reject multiple detector interactions (crosstalk). Beam mask which was made of lead in order to improve spatial resolution and placed on crystal face worked effectively for incident angles from 0 degrees to 15 degrees but degraded uniformity of spatial resolution from 0 degrees to through 30 degrees.     

毛细管电泳高频电导检测器的研制

设计了一种新的毛细管电泳检测器.根据高频电导滴定原理,将电导电极做成两个金属圆筒套于分离毛细管外,并向两个电极施加高频电压.经毛细管分离后的组分流过两个电极之间时,高频电流发生变化,得到毛细管电泳图.该检测器具有应用范围广、操作简便及重现性好等优点,已初步应用于混合无机离子的测定.     

A novel electromagnetic induction detector with a coaxial coil for capillary electrophoresis

A novel electromagnetic induction detector with two inductors for CE was described here.The two inductors were used as signal detection and reference,respectively.The parameters affecting the detector performance(including coil turns,detection distance, excitation frequency,voltage,etc.) were optimized.Under the optimum condition,the feasibility of the detector was examined by analyzing inorganic ions.The fabricated detector showed good linear relationship between the response and the analytes concentrations,with a detection limit of 13μmol/L for Na~+(S/N = 3).A variety of advantages,such as simple construction, ease of operation,and considerably universal response,suggested this novel detector a promising application prospect in analytical area.     

Determination of the fiber-size distribution function in polydisperse dielectric fibrous materials

A simple method has been proposed for determining the average fiber length in unit volume of a polydisperse fibrous material as depending on fiber diameter. The method consists in the measurement of light attenuation as a function of the distance from an examined sample. The method entails comparison of the measured energy fluxes that reach a detector before and after scattering by an examined fibrous material sample and uses an integral relation that expresses the intensity of light transmitted through a random medium via the electric-field correlation function. Formulas have been found for the electric-field correlation function after the passage through a layer of a polydisperse fibrous material with random arrangement and orientation of fibers. The obtained correlation function enables one to derive an integral equation that expresses the logarithmic ratio of the energy fluxes reaching the radiation detector before and after the passage through a scattering medium via the fiber size-distribution function. Solution of this integral equation makes it possible to determine the fiber-size distribution function from the light attenuation measured as depending on the distance from the point of observation. Experiments have been carried out for several fibrous filters and relevant calculations have been presented. The results of the solution of the integral equation agree with the data obtained by other experimental methods and with visual processing of electron micrographs.     

Natural gas pipeline leak detector based on NIR diode laser absorption spectroscopy

The paper reports on the development of an integrated natural gas pipeline leak detector based on diode laser absorption spectroscopy. The detector transmits a 1.653 microm DFB diode laser with 10 mW and detects a fraction of the backscatter reflected from the topographic targets. To eliminate the effect of topographic scatter targets, a ratio detection technique was used. Wavelength modulation and harmonic detection were used to improve the detection sensitivity. The experimental detection limit is 50 ppmm, remote detection for a distance up to 20 m away topographic scatter target is demonstrated. Using a known simulative leak pipe, minimum detectable pipe leak flux is less than 10 ml/min.