Tunable laboratory extended x-ray absorption fine structure system

A new sensitive x-ray monochromator and detector system for performing extended x-ray absorption fine structure (EXAFS) measurements in the laboratory is described. The monochromator combines x-ray focusing optics with rapid elemental tunability. The detection system effectively removes glitches from the data stream, regardless of whether they are due to impurity lines from the x-ray source or if they are due to random instabilities in the incident beam. Used together with a high intensity rotating anode x-ray source, this system can provide synchrotronlike photon intensities, flexibility and resolution, with the easy access and control possible only in the laboratory.     

A laboratory based system for laue micro x-ray diffraction

A laboratory diffraction system capable of illuminating individual grains in a polycrystalline matrix is described. Using a microfocus x-ray source equipped with a tungsten anode and prefigured monocapillary optic, a micro-x-ray diffraction system with a 10 microm beam was developed. The beam profile generated by the ellipsoidal capillary was determined using the "knife edge" approach. Measurement of the capillary performance, indicated a beam divergence of 14 mrad and a useable energy bandpass from 5.5 to 19 keV. Utilizing the polychromatic nature of the incident x-ray beam and application of the Laue indexing software package X-Ray Micro-Diffraction Analysis Software, the orientation and deviatoric strain of single grains in a polycrystalline material can be studied. To highlight the system potential the grain orientation and strain distribution of individual grains in a polycrystalline magnesium alloy (Mg 0.2 wt % Nd) was mapped before and after tensile loading. A basal (0002) orientation was identified in the as-rolled annealed alloy; after tensile loading some grains were observed to undergo an orientation change of 30 degrees with respect to (0002). The applied uniaxial load was measured as an increase in the deviatoric tensile strain parallel to the load axis.     

MEASUREMENT OF FOIL AND CABLE THICKNESSES BY A TRANSMISSION METHOD

X-ray fluorescence analysis techniques can be applied to determine sample thickness by either absolute or relative methods. An absolute method for thickness determination by x-ray fluorescence analysis has been devised, based on two types of independent measurements of the fluorescence intensity of the constituents of the sample and performance of transmission and reflection irradiation setups.

In the present work, a method for determination of the average thickness of material between a gamma-ray source and a detector is presented. The thicknesses of Au, Ag, and Cu foils, and Cu cables have been calculated by a transmission method. An Am-241 radioisotope source and a Si(Li) detector have been used.

The method has high accuracy and is easy to use, it is non-destructive towards the sample, and it allows one to the control the sample thickness. To assess the reliability of the method, the results obtained are compared with the results obtained with a micrometer. The results are in good agreement with each other, within the estimated experimental error     

Specimen coating for high resolution scanning electron microscopy

Thin conducting films, produced by evaporation or soft vacuum sputtering generally show cracks and grain formation, when examined under high resolution scanning electron microscopy (SEM). These artefacts can obscure surface features of coated specimens or cause confusion in the interpretation of micrographs. No such structures have been observed in films produced by ion beam deposition. Ion beam deposition equipment is described in which a cold cathode saddle field ion source, operating at low pressure (15mPa), produces a 2 mm diameter beam of energetic ions (5 keV) and neutrals. With the beam directed onto a target at 30° to glancing incidence, the sputtered material coats the specimens, which are held in a planetary system for good coverage. Conditions favouring fine grain growth are a high nucleation density and low energy transfer to the substrate by thermal conduction or radiation or by particle or photon radiation. These conditions are satisfied by ion beam deposition but evidently not by evaporation or soft vacuum sputtering. With the specimen stationary, sharp shadowing is obtained because the target acts almost as a point source, because of the small diameter of the beam and because there is little scatter at the operating pressure.     

Note: measurement of the runaway electrons in the J-TEXT tokamak

The runaway electrons have been measured by hard x-ray detectors and soft x-ray array in the J-TEXT tokamak. The hard x-ray radiations in the energy ranges of 0.5-5 MeV are measured by two NaI detectors. The flux of lost runaway electrons can be obtained routinely. The soft x-ray array diagnostics are used to monitor the runaway beam generated in disruptions since the soft x-ray is dominated by the interaction between runaway electrons and metallic impurities inside the plasma. With the aid of soft x-ray array, runaway electron beam has been detected directly during the formation of runaway current plateau following the disruptions.     

Single-shot beam-position monitor for x-ray free electron laser

We have developed an x-ray beam-position monitor for detecting the radiation properties of an x-ray free electron laser (FEL). It is composed of four PIN photodiodes that detect backscattered x-rays from a semitransparent diamond film placed in the beam path. The signal intensities from the photodiodes are used to compute the beam intensity and position. A proof-of-principle experiment at a synchrotron light source revealed that the error in the beam position is reduced to below 7 μm by using a nanocrystal diamond film prepared by plasma-enhanced chemical vapor deposition. Owing to high dose tolerance and transparency of the diamond film, the monitor is suitable for routine diagnostics of extremely intense x-ray pulses from the FEL.     

激光等离子体X射线极化光谱研究

为了诊断激光等离子体X射线的极化光谱,研制了一种新型的基于空间分辨的极化谱仪。将平面晶体和球面弯晶色散元件在极化谱仪内正交布置,即在水平通道用PET平面晶体作为色散元件,而在垂直通道用Mica球面弯晶作为色散元件,球面半径为380mm。信号采用成像板进行接收,有效接收面积为30×80mm,从等离子体光源经晶体到成像板的光路约为980mm。物理实验首次在中国工程物理研究院激光聚变研究中心“2×10J激光装置”上进行,成像板获得了铝激光等离子体X射线的光谱空间分辨信号。实验结果表明该谱仪具有较高谱分辨率,适合激光等离子体x射线极化光谱的诊断。     

Electron gun using carbon-nanofiber field emitter

An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10相似文献   

Intercomparison of gamma scattering, gammatography, and radiography techniques for mild steel nonuniform corrosion detection

This paper focuses on the mild steel (MS) corrosion detection and intercomparison of results obtained by gamma scattering, gammatography, and radiography techniques. The gamma scattering non-destructive evaluation (NDE) method utilizes scattered gamma radiation for the detection of corrosion, and the scattering experimental setup is an indigenously designed automated personal computer (PC) controlled scanning system consisting of computerized numerical control (CNC) controlled six-axis source detector system and four-axis job positioning system. The system has been successfully used to quantify the magnitude of corrosion and the thickness profile of a MS plate with nonuniform corrosion, and the results are correlated with those obtained from the conventional gammatography and radiography imaging measurements. A simple and straightforward reconstruction algorithm to reconstruct the densities of the objects under investigation and an unambiguous interpretation of the signal as a function of material density at any point of the thick object being inspected is described. In this simple and straightforward method the density of the target need not be known and only the knowledge of the target material's mass attenuation coefficients (composition) for the incident and scattered energies is enough to reconstruct the density of the each voxel of the specimen being studied. The Monte Carlo (MC) numerical simulation of the phenomena is done using the Monte Carlo N-Particle Transport Code (MCNP) and the quantitative estimates of the values of signal-to-noise ratio for different percentages of MS corrosion derived from these simulations are presented and the spectra are compared with the experimental data. The gammatography experiments are carried out using the same PC controlled scanning system in a narrow beam, good geometry setup, and the thickness loss is estimated from the measured transmitted intensity. Radiography of the MS plates is carried out using 160 kV x-ray machine. The digitized radiographs with a resolution of 50 μm are processed for the detection of corrosion damage in five different locations. The thickness losses due to the corrosion of the MS plate obtained by gamma scattering method are compared with those values obtained by gammatography and radiography techniques. The percentage thickness loss estimated at different positions of the corroded MS plate varies from 17.78 to 27.0, from 18.9 to 24.28, and from 18.9 to 24.28 by gamma scattering, gammatography, and radiography techniques, respectively. Overall, these results are consistent and in line with each other.     

Sub-MeV tunably polarized X-ray production with laser Thomson backscattering

Reported in this article is the generation of unique polarized x-rays in the sub-MeV region by means of the Thomson backscattering of the Nd:YAG laser photon with a wavelength of 1064 nm on the 150 MeV electron from the microtron accelerator. The maximum energy of the x-ray photons is estimated to be about 400 keV. The total energy of the backscattered x-ray pulse is measured with an imaging plate and a LYSO scintillator. The angular divergence of the x-rays is also measured by using the imaging plate. We confirm that the x-ray beam is polarized according to the laser polarization direction with the Compton scattering method. In addition, we demonstrate the imaging of the object shielded by lead with the generated x-rays.     

Quantitative electron probe microanalysis of rough targets: testing the peak-to-local background method

Rough samples with topography on a scale that is much greater than the micrometer dimensions of the electron interaction volume present an extreme challenge to quantitative electron beam x-ray microanalysis with energy-dispersive x-ray spectrometry. Conventional quantitative analysis procedures for flat, bulk specimens become subject to large systematic errors due to the action of geometric effects on electron scattering and the x-ray absorption path compared with the ideal flat sample. The best practical approach is to minimize geometric effects through specimen reorientation using a multiaxis sample stage to obtain the least compromised spectrum. When rough samples must be analyzed, corrections for geometric factors are possible by the peak-to-local background (P/B) method. Correction factors as a function of photon energy can be determined by the use of reference background spectra that are either measured locally or calculated from pure element spectra and estimated compositions. Significant improvements in accuracy can be achieved with the P/B method over conventional analysis with simple normalization.     

Pseudo-rigid-body model for corrugated cantilever beam used in compliant mechanisms

Common compliant joints generally have limited range of motion, reduced fatigue life and high stress concentration. To overcome these shortcomings, periodically corrugated cantilever beam is applied to design compliant joints. Basic corrugated beam unit is modeled by using pseudo-rigid-body method. The trajectory and deformation behavior of periodically corrugated cantilever beam are estimated by the transformation of coordinate and superposition of the deformation of corrugated beam units. Finite element analysis（FEA） is carried out on corrugated cantilever beam to estimate the accuracy of the pseudo-rigid-body model. Results show that the kinetostatic behaviors obtained by this method, which has a relative error less than 6%, has good applicability and corrugated cantilever beam has the characteristics of a large range of motion and high mechanical strength. The corrugated cantilever beam is then applied to design a flexible rotational joint to obtain a larger angle output. The paper proposes a pseudo-rigid-body model for corrugated cantilever beam and designed a flexible rotational joint with large angle output.     

Measures for spectral quality in low-voltage X-ray microanalysis

Characteristic x-ray production with energetic electrons depends strongly on the overvoltage, the ratio of the incident beam energy to the critical excitation energy for the atomic species of interest. Low-voltage x-ray microanalysis (beam energy < or = 5 keV) is especially susceptible to artifacts due to sample charging because the overvoltage is low and even slight charging can strongly affect peak intensities. The Duane-Hunt bremsstrahlung limit is a good diagnostic to detect sample charging. Dynamic charging effects, however, can influence spectra despite an apparently satisfactory Duane-Hunt limit. Dynamic charging effects must be examined by time series experiments, or through use of dynamic energy windows continuously measuring count rates placed across the spectrum. When charging is a problem, conductive surface coatings can eliminate the effects. When pristine surfaces must be examined without coating, the use of a conductive grid can control charging so that useful x-ray spectra can be obtained.     

Soft X-ray coherent scattering: instrument and methods at ESRF ID08

An experimental setup has been developed to perform soft x-ray coherent scattering at beamline ID08 of the European Synchrotron Radiation Facility. An intense coherent beam was obtained by filtering the primary beam with the monochromator and a circular pinhole. A pinhole holder with motorized translations was installed inside the UHV chamber of the diffractometer. The scattered intensity was recorded in reflection geometry with a back-illuminated charge coupled device camera. As a demonstration we report experimental results of resonant magnetic scattering using coherent beam. The degree of coherence is evaluated, and it is shown that, while the vertical coherence is much higher than the horizontal one at the source, the situation is reversed at the diffractometer. The intensity of the coherent beam is also discussed.     

Compact electrostatic levitator for diffraction measurements with a two axis diffractometer and a laboratory x-ray source

A compact electrostatic levitator was developed for the structural analysis of high-temperature liquids by x-ray diffraction methods. The size of the levitator was 200 mm in diameter and 200 mm in height and can be set up on a two axis diffractometer with a laboratory x-ray source, which is very convenient in performing structural measurements of high-temperature liquids. In particular, since the laboratory x-ray source allows a great amount of user time, preliminary or challenging experiments can be performed with trial and error, which prepares and complements synchrotron x-ray experiments. The present small apparatus also provides the advantage of portability and facility of setting. To demonstrate the capability of this electrostatic levitator, the static structure factors of alumina and silicon samples in their liquid phases were successfully measured.     

Talbot-Lau x-ray interferometry for high energy density plasma diagnostic

High resolution density diagnostics are difficult in high energy density laboratory plasmas (HEDLP) experiments due to the scarcity of probes that can penetrate above solid density plasmas. Hard x-rays are one possible probe for such dense plasmas. We study the possibility of applying an x-ray method recently developed for medical imaging, differential phase-contrast with Talbot-Lau interferometers, for the diagnostic of electron density and small-scale hydrodynamic instabilities in HEDLP experiments. The Talbot method uses micro-periodic gratings to measure the refraction and ultra-small angle scatter of x-rays through an object and is attractive for HEDLP diagnostic due to its capability to work with incoherent and polychromatic x-ray sources such as the laser driven backlighters used for HEDLP radiography. Our paper studies the potential of the Talbot method for HEDLP diagnostic, its adaptation to the HEDLP environment, and its extension of high x-ray energy using micro-periodic mirrors. The analysis is illustrated with experimental results obtained using a laboratory Talbot interferometer.     

A new correction method for high-resolution energy-dispersive x-ray analyses in the environmental scanning electron microscope

Spurious x-ray signals, which previously prevented high-resolution energy-dispersive x-ray analysis (EDS) in the environmental scanning electron microscope (ESEM), can be corrected using a simple method presented here. As the primary electron beam travels through the gas in the ESEM chamber, a significant fraction of the primary electrons is scattered during collisions with gas molecules. These scattered electrons form a broad skirt that surrounds the primary electron beam as it impacts the sample. The correction method assumes that changes in the width of the electron skirt with pressure are less important than changes in the skirt intensity; this method works as follows: The influence of the gas on the overall x-ray data is determined by acquiring EDS spectra at two pressures. Subtracting the two spectra provides us with a difference spectrum which is then used to correct the original data, using extrapolation, back to the x-ray spectrum expected under high-vacuum conditions. Low-noise data are required to resolve small spectral peaks; however, the principle should apply equally to x-ray maps and even to low-magnification images.     

Variable rowland radius laboratory vacuum surface-sensitive x-ray absorption fine structure spectrometer

A new laboratory x-ray spectrometer for surface-sensitive extended x-ray absorption fine structure [(S)EXAFS] and surface-sensitive x-ray absorption near-edge structure [(S)XANES] measurements is described. The spectrometer employs a 12 kV mA rotating anode generator. It has a monochromator equipped with a set of exchangeable curved crystals of Johann or Johansson type with different cell parameters, orientations, and Rowland radii. The computer controlled movement system based on nine stepping motors allows all the main elements of the spectrometer to be positioned freely relative to the x-ray source and gives an opportunity to use sophisticated scanning modes (for example, a mode with a focus spot position on a sample surface instead of an exit slit). The whole x-ray beam line is completely enclosed in a vacuum chamber that is directly connected to the x-ray generator, thereby preventing the absorption of x rays in the air. This layout allows a wide x-ray photon energy range from a few keV up to dozens of keV. A registration of x rays transmitted through the sample with proportional counter- and photoelectrons emitted from the sample with channeltron is used to carry out bulk- and surface-sensitive measurements, respectively. Using a 25 x 200 kV mA power regime of a rotating anode x-ray generator, a photon flux of 2.5 x 10(5) counts/s was registered at the Cu K edge, where the energy resolution was about 5 eV. High near surface sensitivity is demonstrated by the EXAFS spectra of Cu K and Hf LIII edges measured from 3 nm Cu and Hf oxide films.     

X-ray magnifier

A method for the magnification of x-ray radiographic images is described and demonstrated. This magnifier employs two successive asymmetric diffractions of an x-ray beam from highly perfect silicon crystals. The two diffractions magnify the beam in two perpendicular directions. A device with a magnification of 25x is demonstrated for Cu K(alpha) radiation. This device preserves and sometimes improves the resolution inherent in the radiographic technique. The x-ray magnifier is particularly useful in circumventing the relatively poor spatial resolution of electro-optical imaging systems needed for real-time observations. Basic limits on magnification and resolution using this method are described.     

Roadmap for the design of a superconducting electron cyclotron resonance ion source for Spiral2

A review of today achieved A∕Q = 3 heavy ions beams is proposed. The daily operation A∕Q = 3 ion beam intensities expected at Spiral2 are at the limit or above best record 3rd generation electron cyclotron resonance ion source (ECRIS) intensities. The necessity to build a new fully superconducting to fulfill these requirements is outlined. A discussion on the volume of the future source is proposed and the minimum value of 12 liters is derived. An analysis of the x-ray absorption superconducting ECRIS is presented based on VENUS experimental data and geometry. This study underlines the necessity to include a complete x-ray study at the time of source conception. The specifications foreseen for the new ECRIS are presented, followed with the roadmap for the design.