Determinations of niobium and palladium resonance cross-sections by time-of-flight transmission experiment

The neutron total cross-sections and resonance parameters of Niobium (Nb) and Palladium (Pd) were measured in the neutron energy regions from 0.1 eV to 100 eV by using the time-of-flight method at the Pohang Neutron Facility, Korea, which consists of an electron linear accelerator, a water-cooled Tantalum (Ta) target with a water moderator, and a 12.06 m long time-of-flight path. A ⁶Li-ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.6 cm was used as a neutron detector, and high purity natural Nb and Pd metallic sheets with thickness of 15 mm (0.0833 atoms/barn) and 1 mm (0.0068 atoms/barn) respectively, were used for the neutron transmission measurements. The notch filters composed of Cobalt (Co), Indium (In), and Cadmium (Cd) were used to estimate the background level and also to calibrate energy. In order to reduce the gamma-ray background from Bremsstrahlung and from neutron capture, we employed a neutron-gamma separation system based on their different pulse shapes. The resonance parameters of ^natNb and ^natPd were obtained from the transmission ratio by using the SAMMY code, which utilizes both Doppler and resolution broadening effects and Bayes’ generalized least squares technique. The present measurements were compared with the existing experimental and the evaluated reactions data files.     

Compton profile of tantalum

The Compton profile of tantalum (Ta) has been measured using IGP type coaxial photon detector. The target atoms were excited by means of 59.54 keV γ-rays from Am-241. The measurements were carried out on a high purity thin elemental foil. The data were recoreded in a 4 K multichannel analyzer. These data duly corrected for various effects are presented and compared with theoretical and measured values. Best agreement with experiment is found for the 5d³6s² electron configuration     

浦项中子装置上209Bi中子全截面测量(英文)

在浦项中子装置(PNF) 的100 MeV电子直线加速器上利用透射法和飞行时间法测量了209Bi 的0.1~100 eV的中子全截面。文中对于实验装置特点、用吸收片法拟合本底、拟合中子飞行距离和时间零点的处理过程做了较为详细的描述。测量结果与以前发表的实验数据以及评价数据ENDF/B-VII.1 做了比较,比较结果符合得较好。     

恒温电热板湿法消解-ICP-AES对地质样品中铌和钽的连续测定

通过恒温电热板加热,用硝酸-氢氟酸-硫酸(体积比为6:5:1,V/V/V)混合酸消解试样,酒石酸定容后用电感耦合等离子体-原子发射光谱法对铌钽矿石中的铌钽连续测定,所加试剂引起的干扰通过空白实验予以消除。铌、钽谱线的发射强度与x(Nb2O5)和x(Ta2O5)在0—8μg/mL的范围内呈良好的线性关系。方法的检出限分别为0.021、0.048μg/mL,方法用于地质样品中铌、钽的分析,加标回收率为95.6%—108.3%,铌和钽的相对标准偏差(n=6)为0.21%—1.56%;用于标准样品分析,测定值与认定值相符。此方法很好的解决了地质调查样品的批量大并要求快速出结果的难题。     

Study of mercury surface diffusion on tantalum with and without an electric field by means of a field emission microscope

The surface diffusion of mercury atoms on tantalum substrate with and without high electric field was studied by means of a field emission microscope (Müller's). The activation energy during surface migration Q_m of mercury atoms with and without an electric field F on tantalum substrate depending on the thickness of the adsorbate was measured. It is shown that the electron density distribution at coverage θ < 0.65 with adsorbate is due to a dipole momentum P. At θ > 0.65 the slope of the curves of Q^F_m = ?(θ) is explained with the appearance of the effect of polarization. The energy of desorption Q_d as a function of the thickness of the adsorbed layer in the temperature range 100–300 K was measured also.     

Optoheterodyne Doppler measurements of the ballistic expansion of the products of the shock wave-induced surface destruction: Experiment and theory

The results of optoheterodyne Doppler measurements of the ballistic expansion of the products of surface destruction under shock-wave loading are presented. The possibility of determining the physical characteristics of a rapidly flying dust cloud, including the microparticle velocities, the microparticle sizes, and the areal density of the dust cloud, is shown. A compact stand for performing experiments on shock-wave loading of metallic samples is described. Shock-wave loading is performed by a 100-µm-thick tantalum flyer plate accelerated to a velocity of 2.8 km/s. As the samples, lead plates having various thicknesses and the same surface roughness are used. At a shock-wave pressure of 31.5 GPa, the destruction products are solid microparticles about 50 µm in size. At a pressure of 42 and 88 GPa, a liquid-drop dust cloud with a particle size of 10–15 µm is formed. To interpret the spectral data on the optoheterodyne Doppler measurements of the expansion of the surface destruction products (spalled fragments, dust microparticles), a transport equation for the function of mutual coherence of a multiply scattered field is used. The Doppler spectra of a backscattered signal are calculated with the model developed for the dust cloud that appears when a shock wave reaches the sample surface at the parameters that are typical of an experimental situation. Qualitative changes are found in the spectra, depending on the optical thickness of the dust cloud. The obtained theoretical results are in agreement with the experimental data.     

Hydrogen desorption from tantalum with segregated oxide surface layers

The combination of thermal desorption spectroscopy (TDS) and Auger electron spectroscopy (AES) was used to examine the correlation between elementary processes on an oxidized tantalum surface and the acceleration of the dehydriding rates at increasing temperatures. We present the TDS of TaD_x foils (foil thickness ~ 25μm) for various initial concentrations (0.038 ⩽ x ⩽ 0.108; α-phase), various heating rates and for high and ultra high vacuum conditions. Activation energies for desorption were derived from the TDS spectra on the assumption that the rate determining process is the recombination of hydrogen atoms to hydrogen molecules at the surface. We find two different activation energies for the low and for the high temperature region. The AES measurements show that the corresponding change in the desorption process is correlated with the dissolution of the segregated oxide surface layer.     

A Fiber Optic Wavelength Modulation Sensor Based on Tantalum Pentoxide Coatings for Absolute Temperature Measurements

A fiber optic low-coherence sensor based on the spectral shift of tantalum pentoxide thin films for absolute temperature sensing up to 650°C is described. A tantalum pentoxide single layer was deposited directly onto the cleaved end-face of a single mode optical fibre and was illuminated with an super luminescence diode (SLD) source through a directional coupler. Interference fringes of the film on reflection were obtained within the optical bandwidth of the SLD using an optical spectrum analyser. The spectral shift versus temperature rise showed no turning points and the output was unambiguous, linear, monotonic and gave about 0.016 nm wavelength shift in the spectrum per°C. A semi-empirical calibration procedure based on the refractive index (n) and thickness (l) of the tantalum pentoxide film for absolute thermometric measurements is described.     

超高速发射中缓冲层材料对钽飞片速度影响的数值分析

 在超高速发射技术研究中,缓冲层材料起着十分重要的作用。通过数值计算,分析了TPX缓冲层材料的厚度对高阻抗钽飞片超高速发射速度的影响,给出了最优的缓冲层材料厚度,对于0.3和0.5 mm厚的钽飞片,选取不同厚度的TPX缓冲层材料,钽飞片中心速度的相对误差达到5%～6%;为了比较不同缓冲层材料对钽飞片速度的影响,还给出了相同厚度的TPX和Lexan材料作缓冲层时,钽飞片的中心速度和压力历史的二维计算结果。     

Structure of β-tantalum-tungsten alloy films produced by the codeposition of sputtered metals

Ion-plasma sputtering and the codeposition of Ta and W ultrafine particles is used to produce solid solutions in the entire concentration range of the Ta-W binary system in the form of alloy coatings. The formation of solid-solution alloys directly during the codeposition process confirms the theory of thermal-fluctuation melting of small particles and the coalescence of quasi-liquid clusters of subcritical size. During the formation of coatings based on Ta and W layers with a thickness less than 0.5 nm mutual dissolution of the components occurs. Starting at a concentration of 34 at % W in the alloy, tungsten atoms specify their own type of crystal-lattice symmetry. Apart from the formation of [beta]-tantalum and tungsten phases, an increase in the thickness of the tantalum and tungsten sublayers leads to the appearance of metal solid solutions, amorphous inclusions, and nanocluster superlattices of one metal in the matrix of another. At high tungsten concentrations a superstructure of tantalum nanoclusters is not observed in the coating. It is supposed that the size factor is the origin of superstructure formation.     

Determination of the optical constants of metals and semiconductors by combining ellipsometry with electron spectroscopy microscopy and X-ray specular reflection analysis

The optical constants n(λ) and k(λ) of metals and semiconductors can be determined by spectroellipsometry, however, their apparent values are considerably affected by the roughness and oxide overlayer thickness dof the sample. Aluminium thin film samples of high perfection and very low roughness (<1 nm) have been studied by cross-disciplinary experimental methods: X-ray specular reflection analysis for determining the structure and thickness of the natural (hydrated) oxide overlayer and roughness of the substrate; plasmon electron energy loss spectroscopy supplied d. For calibration of the d measurements a special thin film multilayer system was developed, suitable for preparing cross-sectional samples for resolution transmission electron microscopy. Knowing the roughness and d-data, the optical constants n(λ) and k(λ) of aluminium were determined by spectroellipsometry in the spectral range λ=365–633 nm. Experimental results and a nomogram are presented for evaluating n(λ) and k(λ). The dependence of the ellipsometric optical constants on roughness and d is discussed. Very good agreement of the optical constants with the corrected ellipsometric results of Blanco and the synchrotron spectroscopy data of Hagemann was found. The cross-disciplinary methods can be applied to metals and semiconductors covered with an overlayer.     

Measurement of the double layer capacitance of aluminium samples by holographic interferometry

In the present investigation, holographic interferometry was utilized for the first time to measure the double layer capacitance of aluminium samples during the initial stage of anodization processes in an aqueous solution without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out chemically in different sulphuric acid concentrations (0.5–3.125% H₂S0₄) at room temperature. In the meantime, a method of holographic interferometry was used to measure the thickness of anodization (oxide film) of the aluminium samples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the double layer capacitance of the aluminium samples in solutions to the thickness of the oxide film of the aluminium samples which forms due to the chemical oxidation. The thickness of the oxide film of the aluminium samples was measured by real-time holographic interferometry. Consequently, holographic interferometry is found to be very useful for surface finish industries, especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film as well as the double layer capacitance of the aluminium samples can be determined in situ. In addition, a comparison was made between the obtained data of the double layer capacitance from the holographic measurements and the double layer capacitance data obtained from measurements of electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data from both techniques.     

流动注射在线液-液萃取-ICP-AES测定土壤和化探样品中痕量铌和钽

应用流动注射在线萃取技术将Nb,Ta萃入甲基异丁酮(MIBK)和磷酸三丁脂(TBP)混合溶剂直接进行ICP-AES测定.研究了流动注射在线萃取-电感耦合等离子体原子发射光谱法测定土壤和化探样品中Nb和Ta的实验条件、流路参数、酸度条件的选择,考察了共存元素的干扰.采样速率为20样@h-1,RSD(n=10)为Nb4.5%;Ta5.1%,测定检出限(K=3)为Nb0.5ng@mL-1;Ta0.8ng@mL-1.方法操作简便、快速,经对国家一级标准物质分析,结果与推荐值一致.     

Étude par spectrométrie Auger de films passifs formes sur le tantale en solution d'acide phosphorique

Elemental in-depth profiles of passivated films formed on electrolytically anodized tantalum in phosphoric acid were constructed from Auger electron spectroscopy N′(E) peaks while ion beam etching the anodized tantalum surfaces. The profiles are shown to be useful in determining the stoichiometry of anodic-oxide layers.The thickness of the passivated films decreases with increasing current density and/or acid concentration for a constant anodization voltage. The film thickness is shown to increase, for given anodization conditions, with increased bath temperatures. The profiles also show that phosphorus from the H₃PO₄ bath is only present at the outermost surface layers of the films.     

Nanocrystalline magnetic PrFeCrB alloys

Ribbons of Pr₅Fe_77−xCr_xB₁₈ (x=0$x=0$, 1, 2, 2.5, 3, 4, 5) were produced by melt spinning and then annealed to develop an enhanced-remanence nanocrystalline magnetic material. These nanocomposites with Cr present a coercive field at least 50% higher than the Cr-free ones, which makes them promising materials for bonded magnets. Four different types of annealing were used in order to develop the nanocrystalline state and to optimize the magnetic properties of these alloys. The first was a conventional annealing, where the ribbons were wrapped in a tantalum foil and annealed in an argon atmosphere, but not encapsulated. The second was a flash annealing, where the ribbons were annealed by passing a current through them. The third was a conventional annealing in an external magnetic field. Finally, the fourth was a conventional annealing, where the ribbons were wrapped in a tantalum foil and encapsulated in quartz tubes with argon gas and then annealed. The annealed samples were studied by magnetic measurements, X-ray diffraction, scanning and transmission electron microscopy and atomic force microscopy. The best magnetic properties are found for Pr₅Fe₇₄Cr₃B₁₈, annealed by the fourth method, which resulted in the lowest oxygen content in the annealed nanocrystalline material as confirmed by scanning electron microscopy. The value for the coercive field for this composition is at least 50% higher than for the material without Cr (≈560 vs. ≈320 kA/m) and 40% higher than for the Nd₂Fe₁₄B/Fe₃B nanocomposite with Cr. Curie temperature measurements and X-ray diffraction data showed that the main phases present in all the samples are Pr₂Fe₁₄B, Fe₃B and α-Fe, Pr₂Fe₁₄B being the majoritary phase. From Curie temperature measurements it was also found that Cr atoms preferentially dissolve in the Fe₃B phase.     

Saturation magnetization of MnBi films with different thicknesses and composition

The saturation magnetization of MnBi films in the low-temperature phase and the quenched high-temperature phase was measured at room temperature by a new method recently described. The measurements were performed with samples of varying thickness and composition (ratio Mn:Bi). The results obtained show no dependence either on film thickness or on composition. Hence, the different magnetization values given in the literature for bulk and thin film samples of the quenched high-temperature phase must not be attributed to a thickness dependence of the samples or to stoichiometric variations. This work has been supported by the data processing program of the Federal Department of Research and Technology of the FRG. The authors alone are responsible for the contents.     

Atomic and Electronic Structures of Intrinsic Defects in Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>: Ab Initio Simulation

The atomic and electronic structure of intrinsic point defects in orthorhombic tantalum oxide has been studied by numerical simulation within the density functional theory. It has been shown that all defects responsible for metal enrichment of Ta₂O₅ serve as electron and hole traps. Under conditions of strong oxygen depletion and at a metal–insulator interface, which are characteristic of resistive memory elements, interstitial tantalum atoms compete with an oxygen vacancy in the formation of a conducting filament. Interstitial oxygen atoms are not involved in charge transport. Tantalum substituting oxygen can be considered as a combination of the oxygen vacancy and interstitial tantalum. The analysis of the calculated thermal and optical energies of trap ionization shows that the oxygen vacancy is a key defect for charge transport in Ta₂O₅.