月球样品的中子活化分析技术研究

月球的起源是月球研究的核心问题。月球探测任务返回的数据和样品极大地提高了人类对地月系统的认知,同时也发现了更多未解之谜,亟待未来的探测任务和科学研究来解答。嫦娥五号月壤是我国首次地外天体采集返回的样品,也是继美国和苏联探月采样任务45年后人类再次获得的月球样品。鉴于月球样品的珍贵性和特殊性,利用先进技术开展其全元素含量的非破坏精准分析对于认识月球演化和月球资源就地开发利用具有重要的意义。依托大型核反应研究堆和加速器中子注量率优势,利用中子活化分析技术可实现月球样品中的全元素非破坏分析：1)仪器中子活化分析技术(INAA)可测量Na—U元素之间的60余种元素;2)瞬发γ中子活化分析技术(PGNAA)可补充测量INAA不适合测量的元素如H、B、C、N等;3)中子深度剖面分析技术(NDP)可测量样品近表面(微米级)聚变能源³He的浓度深度分布;4)缓发中子测量技术(DNC)可定量样品中痕量裂变核素如²³⁵U和²³⁹Pu,并结合INAA可测量²³⁸U/²³⁵U同位素比值;5)14 Me...     

硅酸盐矿物中低含量元素的电子探针异点分步定量法

以电子探针分析硅酸盐矿物国家标准样品 ,研究了不同分析方法和实验条件对硅酸盐矿物的主量元素和质量分数<2 %的低含量元素的电子探针定量分析精度的影响;结果表明 ,在硅酸盐矿物的电子探针定量分析中 ,在假定不含低含量元素的情况下先用常规实验条件分析主量元素的含量 ,尔后用非常规实验条件异点分析低含量元素的含量 ,并让主量元素参与低含量元素定量计算的ZAF校正 ,可以保证不同含量的被测元素均具有较高的分析精度 ,并称该法为“异点分步定量法”。     

质谱检测技术在火星探测中的应用

火星探测对人类寻找地外生命、探索行星产生和演化机制具有重要的科学意义.质谱技术已经在火星探测方面得到了实际应用,获得的数据正在改写着人类对火星的基本认识.本文综述了国内外质谱技术在火星探测任务中的应用现状,特别是我国学者的研究进展、存在问题和应对策略.     

合成甲醇新型合金催化剂的组成与结构特征

本文采用化学分析、BET比表面和孔分布测量、X射线衍射及电子探针技术研究了一氧化碳加氢合成甲醇新型铜锌铝合金催化剂的组成和结构特征。实验结果表明,催化剂比表面较低,但活性表面积比例高,孔分布范围在25—300(?),最可几孔径为90—110(?)。对合成甲醇活性较高的催化剂颗粒进行电子探针元素面扫描,发现其表面元素组成与工业上广泛使用的ICI催化剂基本相同。对与氧化亚氮接触后的催化剂进行X射线衍射测量,发现有明显的氧化亚铜相,由此可以认为,在合金催化剂上零价铜是活性的,而且一价铜也具有相对的稳定性。     

陨石微结构研究

本文利用扫描电子显微镜对吉林、西乌旗、渑池球粒陨石基质、球粒、单矿物及熔壳微结构进行研究,发现了不同类型原生及次生微结构,据此可以区分陨石原生及次生的特点。它们反映了陨石形成过程中经历凝聚、熔融、热变质、重熔、溶蚀、断裂等作用。陨石单矿物中微结构与基质及球粒中相似。     

黔西南卡林型金矿中超微金的微束分析研究

应用同步辐射X射线荧光分析、电子探针及分析电子显微镜等微束分析技术,成功地研究了我国西南几个卡林型金矿中超微金的赋存状态,对所谓的“不可见”金(5—500nm)直接得到了它们的背散射电子像、透射电子像、元素特征X射线面分布和X射线强度分布曲线、特征X射线能谱图及电子探针定量分析结果。     

“733”电子探针对造岩矿物定量分析

本文介绍用“733”电子探针,采用Bence和Albee校正法对造岩矿物如长石类、橄榄石类、石榴石类、辉石类、角闪石类、云母类、绿泥石类、沸石类、粘土、碳酸盐类矿物以及榍石、刚玉、红柱石、十字石、沂濛矿、陨铬辉石、磁铁矿、堇青石等矿物进行大批量的测试,还对“733”电子探针定量分析中几个比较重要问题:镀膜技术;对碱金属元素和含水矿物的分析;标样的选择;对分析样品的要求;测试条件的选择进行了分析和讨论。     

碱熔-电感耦合等离子体质谱法测定硫铁矿单矿物中的金、银及铂族元素

<正>单矿物分析在地质样品分析中属于较难解决的问题之一,原因是现成的分析方法少。而单矿物中微量元素的地球化学特征研究又需要矿物成分中微量元素含量的准确测定。铂族元素可以作为一种新的地球化学示踪剂,对岩石学特征和地幔源区的演化提供重要的信息。铂族元素通常采用火试金的方法测定[1-5],需要至少20g以上的样品,而单矿物的样品量通常比较少。这就要求用较少的试样量,不仅提供矿物主成分,而且要测定多种痕量元素,铂族     

钢中大尺寸稀土夹杂物的形成动力学研究

以添加稀土等微合金化元素的5CrNiMo钢为例, 通过电子探针元素面分布分析探讨了钢中大尺寸稀土夹杂物的成分和组成元素的分布规律, 初步探明了稀土夹杂物的形成动力学及形成机制. 研究结果表明: 稀土夹杂物首先以高熔点氧化物和硫化物为核心分别独立形核长大, 然后以稀土所特有的较高表面活性在液相和凝固过程中相结合, 最终细小分散的稀土夹杂物合并成一个大尺寸的稀土夹杂物.     

中国先进研究堆瞬发γ元素成像技术研究

无损分析样品内部的元素分布,对于材料、考古、地质科学等领域的研究具有重要意义。本文基于瞬发γ活化分析方法,结合中子照相技术,分析了模拟样品的结构和对称性,首次利用中国先进研究堆(CARR)水平孔道聚焦的微束中子束流,开展了样品瞬发γ扫描分析和材料内部元素分布研究。通过蒙特卡罗软件(MCNP)对样品元素分布实验模型进行分析,模拟结果获得了样品不同区域的元素分布,基本实现了元素空间分辨。MCNP计算结果表明在瞬发γ扫描分析中,优化准直几何参数和提高中子通量能进一步提高元素空间分辨和元素测量准确度。     

Determination of the sulphur content of a lunar sample by neutron capture gamma-ray spectrometry

The technique of prompt neutron capture gamma-ray spectroscopy has been used to determine sulphur concentrations in extraterrestrial materials. In particular an effort was made to resolve reported discrepancies in the sulphur assays for the lunar rock sample 70215. While the validity of chemical analysis techniques are often influenced by the chemical form of the sulphur, particularly when in low concentration, the method used here is independent of such effects. The lunar and a bulk Allende meteorite sample were analyzed for sulphur, iron and silicon. The latter material, being well documented, was analyzed in order to verify the techniques of measurement and the subsequent methods of data reduction. Based upon our measurements and the acceptance of the silicon and iron content of the lunar sample the sulphur content was found to be 1741±112 ppm by weight.     

Detection and visualisation of elemental components in various ambient species by synchrotron microbeam technique

This study introduces the application of the synchrotron radiation induced X-ray fluorescence (SR-XRF) microprobe installed at the Super Photon ring-8 GeV (SPring-8), which is the world's largest third-generation synchrotron radiation facility, to the specification of chemical properties of various atmospheric samples. The combination of visual elemental mapping and XRF spectral analyses allows for the interpretation of the nature and composition of individual particles. Individually collected droplets by the replication technique were also irradiated by X-ray microbeam to carry out visual reconstruction of elemental maps for their multiple components. The multielemental peaks corresponding to X-ray energy were also successfully resolved. Because the chemical contents of solute for individual droplets can be definitely clarified in this study, we can describe the mechanisms involved in droplet formation and pollutant scavenging. The point analysis of sand dust collected from the local desert in China confirmed that the fine fragments of sand, which may be lifted and transported over a long distance, are considerably inhomogeneous in elemental component.     

Understanding prebiotic chemistry through the analysis of extraterrestrial amino acids and nucleobases in meteorites

The discoveries of amino acids of extraterrestrial origin in many meteorites over the last 50 years have revolutionized the Astrobiology field. A variety of non-terrestrial amino acids similar to those found in life on Earth have been detected in meteorites. A few amino acids have even been found with chiral excesses, suggesting that meteorites could have contributed to the origin of homochirality in life on Earth. In addition to amino acids, which have been productively studied for years, sugar-like molecules, activated phosphates, and nucleobases have also been determined to be indigenous to numerous meteorites. Because these molecules are essential for life as we know it, and meteorites have been delivering them to the Earth since accretion, it is plausible that the origin(s) of life on Earth were aided by extraterrestrially-synthesized molecules. Understanding the origins of life on Earth guides our search for life elsewhere, helping to answer the question of whether biology is unique to Earth. This tutorial review focuses on meteoritic amino acids and nucleobases, exploring modern analytical methods and possible formation mechanisms. We will also discuss the unique window that meteorites provide into the chemistry that preceded life on Earth, a chemical record we do not have access to on Earth due to geologic recycling of rocks and the pervasiveness of biology across the planet. Finally, we will address the future of meteorite research, including asteroid sample return missions.     

Analysis of <Superscript>26</Superscript>Al in meteorite samples by coincidence gamma-ray spectrometry

Large volume Ge-detectors have been used for the analysis of positron emitters of cosmogenic origin in extraterrestrial samples including lunar samples and meteorites. We present results from the analysis of ²⁶Al in the Rumanová chondrite which was found in 1994 in Slovakia. A slide of the meteorite was cut into ~1 cm³ cubes which were analyzed in a coincidence Ge–NaI(Tl) spectrometer placed in a large shield measuring 1.5 × 1.5 × 2 m³, and consisting of iron, lead and copper layers. Operational characteristics of the spectrometer are presented and discussed, as well as the ²⁶Al profile observed in the meteorite.     

Use of standard reference materials as multielement irradiation standards in neutron activation analysis

Standard reference materials, normally used to check accuracy and precision of analytical methods or for interlaboratory comparisons, are proposed for use as multielement irradiation standards in neutron activation analysis (NAA). The advantages are simplicity of operation, and elimination of errors inherent in the preparation of a large number of synthetic standards at the trace element level. Examples of the approach are illustrated in the analysis of geological materials, soils, sediments, meteorites, lunar samples, coal and fly ash using the USGS diabase W-1 as the irradiation standard. Plant materials and animal tissue are analyzed using NBS Orchard Leaves as the irradiation standard. Best values for four popular SRM's (W-1, Bowen's Kale, Orchard Leaves, and Bovine Liver) are tabulated to facilitate further use of the proposed approach to multielement neutron activation analysis.     

Microchip capillary electrophoresis instrumentation for in situ analysis in the search for extraterrestrial life

The search for signs of life on extraterrestrial planetary bodies is among NASA's top priorities in Solar System exploration. The associated pursuit of organics and biomolecules as evidence of past or present life demands in situ investigations of planetary bodies for which sample return missions are neither practical nor affordable. These in situ studies require instrumentation capable of sensitive chemical analyses of complex mixtures including a broad range of organic molecules. Instrumentation must also be capable of autonomous operation aboard a robotically controlled vehicle that collects data and transmits it back to Earth. Microchip capillary electrophoresis (μCE) coupled to laser-induced fluorescence (LIF) detection provides this required sensitivity and targets a wide range of relevant organics while offering low mass, volume, and power requirements. Thus, this technology would be ideally suited for in situ studies of astrobiology targets, such as Mars, Europa, Enceladus, and Titan. In this review, we introduce the characteristics of these planetary bodies that make them compelling destinations for extraterrestrial astrobiological studies, and the principal groups of organics of interest associated with each. And although the technology we describe here was first developed specifically for proposed studies of Mars, by summarizing its evolution over the past decade, we demonstrate how μCE-LIF instrumentation has become an ideal candidate for missions of exploration to all of these nearby worlds in our Solar System.     

Elemental imaging at the nanoscale: NanoSIMS and complementary techniques for element localisation in plants

The ability to locate and quantify elemental distributions in plants is crucial to understanding plant metabolisms, the mechanisms of uptake and transport of minerals and how plants cope with toxic elements or elemental deficiencies. High-resolution secondary ion mass spectrometry (SIMS) is emerging as an important technique for the analysis of biological material at the subcellular scale. This article reviews recent work using the CAMECA NanoSIMS to determine elemental distributions in plants. The NanoSIMS is able to map elemental distributions at high resolution, down to 50 nm, and can detect very low concentrations (milligrams per kilogram) for some elements. It is also capable of mapping almost all elements in the periodic table (from hydrogen to uranium) and can distinguish between stable isotopes, which allows the design of tracer experiments. In this review, particular focus is placed upon studying the same or similar specimens with both the NanoSIMS and a wide range of complementary techniques, showing how the advantages of each technique can be combined to provide a fuller data set to address complex scientific questions. Techniques covered include optical microscopy, synchrotron techniques, including X-ray fluorescence and X-ray absorption spectroscopy, transmission electron microscopy, electron probe microanalysis, particle-induced X-ray emission and inductively coupled plasma mass spectrometry. Some of the challenges associated with sample preparation of plant material for SIMS analysis, the artefacts and limitations of the technique and future trends are also discussed.     

X-ray mapping in electron-beam instruments.

This review traces the development of X-ray mapping from its beginning 50 years ago through current analysis procedures that can reveal otherwise obscure elemental distributions and associations. X-ray mapping or compositional imaging of elemental distributions is one of the major capabilities of electron beam microanalysis because it frees the operator from the necessity of making decisions about which image features contain elements of interest. Elements in unexpected locations, or in unexpected association with other elements, may be found easily without operator bias as to where to locate the electron probe for data collection. X-ray mapping in the SEM or EPMA may be applied to bulk specimens at a spatial resolution of about 1 microm. X-ray mapping of thin specimens in the TEM or STEM may be accomplished at a spatial resolution ranging from 2 to 100 nm, depending on specimen thickness and the microscope. Although mapping has traditionally been considered a qualitative technique, recent developments demonstrate the quantitative capabilities of X-ray mapping techniques. Moreover, the long-desired ability to collect and store an entire spectrum at every pixel is now a reality, and methods for mining these data are rapidly being developed.     

Characterization of small particles by micro X-ray fluorescence

Micro X-ray fluorescence was used to study both homogeneous and heterogeneous particle systems. Specifically, homogeneous glass microspheres and heterogeneous soil particle samples were prepared by both bulk and single particle sample preparation methods for evaluation by micro X-ray fluorescence. Single particle sample preparation methods allow for single particles from a collected sample to be isolated and individually presented to the micro X-ray fluorescence instrument for analysis. Various particle dispersion methods, including immobilization onto Tacky Dot™ slides, mounting onto double-sided sticky tape affixed to polypropylene film, or attachment to polypropylene film using 3M Artist's Adhesive, were used to separate the sample particles for single particle analysis. These methods were then compared and evaluated for their ability to disperse the particles into an array of single separated particles for optimal micro X-ray fluorescence characterization with minimal background contribution from the particle mounting surface. Bulk methods of particle sample preparation, which included pellet preparation and aerosol impaction, used a large quantity of collected single particles to make a single homogeneous specimen for presentation to the instrument for analysis. It was found that single particle elemental analysis by micro X-ray fluorescence can be performed if the particles are well separated (minimum separation distance = excitation source beam diameter) down to a particle mass of ∼ 0.04 ng and a mean particle diameter of ∼ 0.06 μm. Homogeneous particulates can be adequately characterized by micro X-ray fluorescence using either bulk or single particle analysis methods, with no loss of analytical information. Heterogeneous samples are much harder to characterize, and both single particle as well as bulk analyses must be performed on the sample to insure full elemental characterization by micro X-ray fluorescence.