Low-level measurement of alpha-particle emitting nuclei in ceramics and lead

The operationally defined bioavailable fraction from a commonly used sequential extraction (SE) procedure was compared to biological availability represented by plant uptake of¹³⁷Cs and⁹⁰Sr. Experiments were conducted at two locations in the Ukraine and at several field locations on the Savannah River Site, South Carolina. A significant regression existed between plant uptake and the ammonium acetate fraction (r ²=0.65), however, ratios of predicted uptake from the SE procedure to observed plant uptake ranged from 0.03 to 5.2 Data suggest that SE procedure was useful for qualitative interpretations of biological availability but lacked sufficient rigor to be useful for quantitative predictions.     

Development and test of a new Knudsen effusion apparatus for the measurement of low vapour pressures

A new Knudsen effusion apparatus based on the mass-loss technique was developed. The apparatus was designed for the measurement of vapour pressures below 1 Pa, at temperatures between 250 K and 470 K, using simultaneously up to seven effusion cells. The quality of the results obtained with this new apparatus was verified through the study of two reference compounds, anthracene and phenanthrene. Both the measured vapour pressures and the derived standard molar enthalpies of sublimation are in excellent agreement with values available in the literature for these compounds.     

Surface Phenomena in the Ionization Chamber of the Mass Spectrometer Ion Source

High Energy Chemistry - The resonance interaction of ionizing electrons with 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules was studied by negative-ion mass spectrometry. The installation of an...     

微小型氢火焰离子化检测器及在色谱中的应用

构建了一种微小型氢火焰离子化检测器(μ-FID).与传统FID不同,助燃空气从收集极上部侧面导入,沿收集极与检测器壳体之间的缝隙向下流动,以环状气流沿壁流入燃烧室,流向反转后从中空的收集极内流出.火焰喷口位于燃烧腔的正中心轴线上,该区域助燃气的流动非常稳定,因此噪音电平非常低.采用更高的极化电压以提高离子化效率.对喷口材料及其内径、收集极长度、收集极至喷口的距离等结构参数进行了优化.在最优条件下,极化电压800 V时,检测器的信噪比比极化电压为150 V时提高一个数量级以上,检出限达1×10-12 g/s.相对于常规FID,μ-FID的气体消耗降低了70%,仅需要氢气和空气两种气体;具有体积小、重量轻、结构简单、灵敏度高、成本低廉等优点,适合作为便携式微型色谱的通用型检测器.     

Calibration of the LNMRI Secondary Standard Ionization Chamber for 131I capsules used in nuclear medicine

The radionuclide ¹³¹I has been increasingly used in nuclear medicine therapy procedures. Nowadays, the ¹³¹I source administered to the patient is manufactured in two different geometries: solution and capsules. The purpose of this study is the accurate measurement of the activity present in a ¹³¹I capsule without destroys it. The methodology to determine the capsules activity is to obtain the calibration factor of an IG12 secondary standard activity measurement system based on the IG12 well-type ionization chamber set up at Brazilian national metrology laboratory for ionizing radiation (LNMRI) of institute of radiation protection and dosimetry (IRD).The result obtained, 6.4670?±?0.0381?×?10^?18?A?Bq^?1, is quite similar to the calibration factor of the ¹³¹I solution contained in the standard ampoule geometry, 6.4515?±?0.0368?×?10^?18?A?Bq^?1. After obtaining the calibration factor it was used to measure ¹³¹I therapy capsules in order to check the performance of radionuclide calibrators of some Brazilian nuclear medicine centers.     

ALFITeX: a new code for the deconvolution of complex alpha-particle spectra

A new code for the deconvolution of complex alpha-particle spectra has been developed. The ALFITeX code is written in Visual Basic for Microsoft Office Excel 2010 spreadsheets, incorporating several features aimed at making it a fast, robust and useful tool with a user-friendly interface. The deconvolution procedure is based on the Levenberg–Marquardt algorithm, with the curve fitting the experimental data being the mathematical function formed by the convolution of a Gaussian with two left-handed exponentials in the low-energy-tail region. The code also includes the capability of fitting a possible constant background contribution. The application of the singular value decomposition method for matrix inversion permits the fit of any kind of alpha-particle spectra, even those presenting singularities or an ill-conditioned curvature matrix. ALFITeX has been checked with its application to the deconvolution and the calculation of the alpha-particle emission probabilities of ²³⁹Pu, ²⁴¹Am and ²³⁵U.     

超声喷雾电离源的研制与表征

研制了超声喷雾电离源(SSI)。采用核糖核酸A、溶菌酶等样品和商品化的线性离子阱质谱仪对该电离源进行了表征。实验发现,对于生物大分子,超声喷雾电离质谱(SSI-MS)能够获得与电喷雾质谱(ESI-MS)类似的多电荷离子。但与同等条件下ESI-MS所获得的谱图相比,SSI主要获得低价态的多电荷离子。在此基础上,系统考察了SSI-MS各主要操作参数对不同价态蛋白质多电荷离子信号强度的影响,并提出了SSI离子化的可能机理。结果表明,在喷雾气压3.4~3.6 MPa、喷雾口到质谱入口的距离4~6 mm、离子传输管温度250~300℃、样液流速50~100μL/min、2%~5%甲酸酸性且不含甲醇的条件下,各价态蛋白质离子信号强度及信号分布均达到最优;而离子传输管温度越高,喷雾压力越大或溶剂中甲醇等挥发性成分越高,则越有利于低价态离子的形成。     

氧-火焰离子化检测器的研制及应用

本文介绍选择测定复杂有机混合物中各含氧化合物的氧-火焰离子化(O-FID)检测器,该仪器是专门对氧响应的O-FID检测器,还报道了在O-FID检测器上对含氧化合物的定量校正工作。     

电离学说的发展历程及启示

系统地研究了电离学说的发生、发展过程,发现电离学说与电解质溶液理论相伴发生、发展;电离学说的发展历程可分为4个历史阶段：对溶液的早期认识、电化学重要概念的提出、电离理论的提出、电离学说的完善。     

微小型氢火焰离子化检测器及在色谱中的应用

构建了一种微小型氢火焰离子化检测器(μ-FID).与传统FID不同,助燃空气从收集极上部侧面导入,沿收集极与检测器壳体之间的缝隙向下流动,以环状气流沿壁流入燃烧室,流向反转后从中空的收集极内流出.火焰喷口位于燃烧腔的正中心轴线上,该区域助燃气的流动非常稳定,因此噪音电平非常低.采用更高的极化电压以提高离子化效率.对喷口...     

Development and testing of a comprehensive chemical mechanism for the oxidation of methane

A comprehensive chemical mechanism to describe the oxidation of methane has been developed, consisting of 351 irreversible reactions of 37 species. The mechanism also accounts for the oxidation kinetics of hydrogen, carbon monoxide, ethane, and ethene in flames and homogeneous ignition systems in a wide concentration range. It has been tested against a variety of experimental measurements of laminar flame velocities, laminar flame species profiles, and ignition delay times. The highest sensitivity reactions of the mechanism are discussed in detail and compared with the same reactions in the GRI, Chevalier, and Konnov mechanisms. Similarities and differences of the four mechanisms are discussed. The mechanism is available on the Internet as a fully documented CHEMKIN data file at the address http://www.chem.leeds.ac.uk/Combustion/Combustion.html . © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 513–538, 2001     

Future direction for measurement,testing and conformity assessment

Measurement and testing are of fundamental importance to science, technology and the economy. There is no science without measurements, no quality without testing and no global market without standards. This article tries to look into the future for the testing community. Based on the anticipated changes in the environment for the testing activities a prediction of the coming technical development as well as acceptance of test results is given. Also the future of accreditation is discussed.     

Utilization of steel plates from abolished old metallurgical factory for shielding of low activity measurement devices

Steel plates about 80 years old from abolished rolling workshops of the POLDI factory at Kladno, Czechoslovakia, can be utilized for the construction of shielding in low activity measurement devices.     

电化学电喷雾电离源控制系统的研制

控制系统是电化学电喷雾电离源的核心部件及研制难点.本研究通过单片机控制数模、模数转换及蓝牙无线通讯模块构建了一套电化学电喷雾电离源(EC/ESI source)的控制系统.利用此系统及一种同轴式探针组成了完整的电化学电喷雾电离源,对9,10-二苯基蒽进行了循环伏安及在线电化学/电喷雾电离质谱(Online EC/ESI-MS)测试.结果表明:此系统具有高达±1 mV的电势控制精度,电流测量精度优于±0.1 μA(增益为0.01 V/μA)或±0.01 μA(增益为0.1 V/μA).本系统具有成本低廉,可在电喷雾高压上安全悬浮,易于操控的特点.     

台式大气压离子源飞行时间质谱仪的研制及性能表征

自制了一款台式大气压离子源飞行时间质谱仪。该仪器采用垂直引入式结构,主要由离子源、大气压接口、离子传输装置及质量分析器组成,其中分析器长度为550 mm。以电喷雾离子源对仪器性能进行表征:仪器在m/z 38.96、132.91、609.28、1 009.58处获得的分辨率分别为4 200、4 900、6 000、7 500;可明显测到甲醇的[CH3OH+H]+峰(m/z 33)和PEG1500的[HO(CH2CH2O)39H+Na]+峰(m/z 1 758);绘制了利血平离子在质荷比609处的峰面积与样品浓度间的标准曲线,其动态线性范围为1~200 pg/μL;信噪比为3时,方法的检出限为1 pg/μL。大气压接口的分子离子反应装置通过碰撞诱导解离效应获得了样品的碎片离子,可用于样品的分子结构分析。该仪器能与多种常压电离技术联用,有望用于药品、环境、食品等领域。     

Field testing of collection and measurement of radioxenon for the Comprehensive Test Ban Treaty

Pacific Northwest National Laboratory, with guidance and support from the U.S. Department of Energy's NN-20 Comprehensive Test Ban Treaty (CTBT) Research and Development program, has developed and demonstrated a fully automatic sampler-analyzer (ARSA) for the collection and quantitative measurement of the four xenon radionuclides,^131mXe (11.9 d),^133mXe (2.19 d),¹³³Xe (5.24 d), and¹³⁵Xe (9.10 h), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a CTBT, and may have applications in stack monitoring and other areas where xenon radionuclides are present. The activity ratios between certain of these radionuclides permit discrimination between radioxenon originating from nuclear detonations and that from nuclear reactor operations, nuclear fuel reprocessing, or from medical isotope production and usage. With the ARSA system, xenon is continuously and automatically separated from the atmosphere at flow rates of about 100 lpm by sorption-bed techniques. Samples collected in 8 hours are automatically analyzed by electron-photon coincidence spectrometry to provide detection sensitivities as low as 100 μBq/m³ of air. This sensitivity is about 10-fold better than achieved with reported laboratory-based procedures¹ for the short time collection intervals of interest. Gamma-ray energy spectra and gas analysis data are automatically collected.     

Lanthanum fluoride coprecipitation technique for the preparation of actinides for alpha-particle spectrometry

A simple and rapid procedure is described by which actinides can be mounted in a form suitable for alpha-particle spectrometry without recourse to electrodeposition. The actinides are coprecipitated as fluorides with 100 g of lanthanum carrier from an acidic solution. The precipitate is mounted on a 0.1 -pore membrane filter containing LaF₃ substrate, also prepared from 100 g of lanthanum. The resolution obtained using samples of pure radiotracers and of frations isolated from lake sediments is generally comparable to that afforded by the conventional electrodeposition technique. The coprecipitation yield is generally quantitative. The entire procedure can be completed in about 90 min.     

On-site determination of formaldehyde: a low cost measurement device for museum environments

A trapping reagent for formaldehyde, based on the pararosaniline reaction, was evaluated as a method of determination of formaldehyde in the aqueous or vapour phase. Collection of formaldehyde vapour relied upon passive diffusion of formaldehyde into the trapping media and quantitative results were obtained without the need for liquid impingers, bubblers or active sampling pumps. Moreover, a novel, hand-held absorption spectrophotometric measurement device was designed to provide on-site, quantitative measurements. It is proposed that the full measurement system devised would be ideally suited to specific sampling applications such as those found in museum enclosures.     

Matrix Assisted Ionization in Vacuum, a Sensitive and Widely Applicable Ionization Method for Mass Spectrometry

An astonishingly simple new method to produce gas-phase ions of small molecules as well as proteins from the solid state under cold vacuum conditions is described. This matrix assisted ionization vacuum (MAIV) mass spectrometry (MS) method produces multiply charged ions similar to those that typify electrospray ionization (ESI) and uses sample preparation methods that are nearly identical to matrix-assisted laser desorption/ionization (MALDI). Unlike these established methods, MAIV does not require a laser or voltage for ionization, and unlike the recently introduced matrix assisted ionization inlet method, does not require added heat. MAIV-MS requires only introduction of a crystalline mixture of the analyte incorporated with a suitable small molecule matrix compound such as 3-nitrobenzonitrile directly to the vacuum of the mass spectrometer. Vacuum intermediate pressure MALDI sources and modified ESI sources successfully produce ions for analysis by MS with this method. As in ESI-MS, ion formation is continuous and, without a laser, little chemical background is observed. MAIV, operating from a surface offers the possibility of significantly improved sensitivity relative to atmospheric pressure ionization because ions are produced in the vacuum region of the mass spectrometer eliminating losses associated with ion transfer from atmospheric pressure to vacuum. Mechanistic aspects and potential applications for this new ionization method are discussed.      

Development of a HPTLC method for in-process purity testing of pentoxifylline

A HPTLC method for the separation and identification of pentoxifylline and related substances, impurities of reaction partners, and side reaction products has been developed using different mobile and stationary phases. For quantitative assay of possible by-products as impurities, LiChrospher RP-18 F254s chromatoplates, acetone-chloroform-toluene-dioxane (2:2:1:1 v/v) as a mobile phase, and detection at 275 nm were employed. Linearity (r > or = 0.997), recovery (86.5-115.5%), and determination limit (0.1-0.6%) were evaluated and found to be satisfactory. This method enables monitoring of the synthesis, as well as purity control of pentoxifylline-containing raw materials and pharmaceuticals.