Ta Foil Research Articles

Two-photon coincidence studies of highly-charged ion relaxation in solids

We studied the relaxation of hollow atoms by two-photon transitions during the stopping of slow (E=8.5q keV) highly charged Pbq+ (q=53–58) ions in a thin Ta foil. The X-rays emitted during the relaxation process were detected in coincidence with two Si(Li) detectors. Particular attention was paid to the role of the internal dielectronic excitation (IDE) in the relaxation dynamics. We found a clear contribution to relaxation by the IDE process also for projectiles with initial M-shell vacancies and IDE speeds up relaxation of electrons from high Rydberg states by directly filling vacancies in the N-shell that is accompanied with the excitation of M-shell electrons. We discuss the relaxation mechanism, and present results for the fluorescence yield and the IDE probability of highly charged Pb ions in a solid.

Performance of FCCI barrier foils for U–Zr–X metallic fuel

Diffusion couple tests of U–Zr or U–Zr–Ce alloys vs. ferritic martensitic steels such as HT9 or T91 were carried out in order to evaluate the performance of the diffusion barrier candidates. Elemental metal foils of Zr, Nb, Ti, Mo, Ta, V and Cr were very effective in inhibiting interdiffusion between these fuels and steels. Eutectic melting between the fuels and steels was not observed in any of the diffusion couples using these diffusion barrier foils at annealing temperatures up to 800 °C. Among the metallic foils evaluated in this study, V and Cr exhibited the most promising performances as a diffusion barrier material for eliminating the fuel cladding chemical interaction problem. However, Zr, Nb and Ti showed an active interaction with the fuel mainly due to the large U solubility.

A simple Cu-64 production and its application of Cu-64 ATSM

One of the positron emission radionuclides, 64Cu, has been reported to be a particularly effective radioisotope in PET imaging study. This utility of 64Cu depends on the chemical stability in water with proper energy and half-life as γ-emitters. Hence, we tried to develop a simple method for producing this isotope using an old cyclotron model in our site (50 MeV, Scantronics co.). In particular, we designed the equipments of enrich 64Ni plating system and radioactive 64Cu separation using plastic cartridge column; 64Ni plating system on gold foil which located in the 13° angle target toward beam irradiation. For the nuclear reaction of 64Cu, it was applied to 64Ni(p, n) 64Cu at low energy under the degrader composed of Al and Ta foils. After beam irradiation, 64Cu was identified by multichannel analyzer installed for a HPGe detector and its utility was certified by the microPET images of 64Cu-ATSM (CT-26 tumor bearing mouse as reported previously). The image quality of 64Cu was also very similar to that of 18F radioisotope in microPET scanner. In conclusion, a method of 64Cu production and its application was successfully established in old cyclotron having high energy.

Decrease in Patient Radiation Exposure by a Tantalum Filter during Electrophysiological Procedures

Minimization of X-ray exposure remains a primary issue in cardiac electrophysiology. The effectiveness of X-ray beam filtration during cardiac electrophysiological procedures was therefore studied, using a 0.05-mm-thick tantalum (Ta) foil, as a filter on the primary X-ray beam, to reduce the patient dose without degradation of image quality. Preliminary tests were made on a phantom developed with polymethylmethacrylate, catheters, and guide wires. The filter was then used in patients during cardiac procedures. Identical patient images were obtained with and without the Ta filter insertion and the ratio between image quality and patient dose was evaluated. Changes in patient dose and signal-to-noise ratio, as image quality index were measured on the phantom and in patients. When the Ta filter was used, the mean effective individual patient dose decreased by 3 to 40% (mean reduction = 27%), with no perceivable difference in image quality estimated by electrophysiologists. This Ta filter may be useful to limit the radiation exposure of patients and operators during cardiac procedures.

Self-Assembled Fabrication of Vertically Oriented Ta2O5 Nanotube Arrays, and Membranes Thereof, by One-Step Tantalum Anodization

We report for the first time synthesis of high-aspect-ratio tantalum oxide nanotube arrays via one-step anodization of Ta foil. The use of aqueous electrolytes containing HF:H2SO4 in the volumetric ratios 1:9 and 2:8 results in formation of ordered nanodimpled surfaces with 40−55 nm pore diameters over the potential range 10−20 V. The addition of 5−10% of either ethylene glycol (EG) or dimethyl sulfoxide (DMSO) to the HF and H2SO4 aqueous electrolytes resulted in the formation of Ta oxide nanotube arrays up to ∼20 μm thick, either securely anchored to the underlying Ta film or as robust free-standing membranes, as dependent upon the anodization time and applied voltage.

Fabrication of Multiple Slit Using Stacked-Sliced Method for Hard X-ray Talbot–Lau Interferometer

We propose using a multiple slit fabricated by a simple and economical stacked-sliced method for X-ray phase imaging with a Talbot–Lau X-ray interferometer. Foils of Ta and Al were stacked alternately, and the stack was sliced up perpendicular to the stacking direction. We successfully fabricated a hard X-ray multiple slit with a space size (Al foil thickness) of about 10 µm and an aspect ratio of 60. Optical microscopy evaluation showed its regular pitch pattern at its surface. A high-resolution X-ray transmission image proved the regularity of the inner part. The visibility of moiré fringes and the phase-contrast image obtained using the Talbot–Lau interferometer with the multiple slit proved the feasibility of the stacked-sliced approach.

積層クラッドを用いたMoおよびNbに対するアルミナイド被膜の作製

In order to improve the oxidation resistances of Mo and Nb alloys, aluminide coatings were developed by lamination cladding. Mo, Nb, and Al sheets with a purity of 99.99 wt% and dimensions of 15 mm×10 mm×0.5 mm were prepared by cutting, followed by the development of a specimen piece by holding the Al sheet between two sheets of Mo or Nb. The specimen wrapped with a Ta foil to prevent oxidation was heated at temperatures of the order of the melting point of Al in a pure Ar atmosphere. On the basis of the elemental analysis by characteristic X-rays, the laminated layers formed on the Mo substrates were found to be composed of MoAl5, MoAl4, and Mo3Al8. It was also found that the main phase constituting the laminated layers changed from MoAl5 to Mo3Al8 on increasing the temperature from 973 K to 1473 K. In contrast, NbAl3 was singly formed on the Nb substrate, irrespective of the heating temperatures. However, since NbAl3 grains have a spherical shape, the NbAl3 layer was not formed on the Nb substrate.

Comparisons for the resistivity behaviors of different encapsulated MgB 2 samples

We report the comparisons of the effect on the resistivity behaviors for the four different encapsulated MgB 2 samples where we optimized the pure MgB 2, using the same standard solid-state synthesis technique, with different shielding materials. The encapsulations were done in Fe Tube, Ta Tube, Ta Foil and Mo Foil, respectively. For the overall comparison, Fe Tube encapsulation seems better sample than others. The lattice parameters ‘ a’ and ‘ c’ were found to be of the same order. The XRD patterns showed that the compound depicted the single-phase, which are crystallized in the hexagonal structure (space group P 6/ mmm) at room temperature, exhibited T c of around 37–39 K. We could not completely avoid the inclusion of the foreign particles in our samples, despite having used several encapsulations, but the sample synthesized by this method holds the easiest way to attain better superconducting polycrystalline bulk MgB 2.

Formation of Co ultrathin films on Si(1 1 1): Growth mechanisms, electronic structure and transport

The AES, EELS, AFM and resistance measurement investigations have been performed to determine the growth mechanism, electronic structure and resistance-thickness dependence of Co layers on silicon at the thickness range from submonolayer up to several monolayer coverage. These layers were obtained under UHV high-rate deposition with using re-evaporation of Co from a Ta foil. The layer-by-layer growth of Co on Si(1 1 1) with some light segregation of Si has been found on the AES data. An enlarged and reduced concentration of valence electrons in the interface Si layer at the thickness ranges 0–1 Å and in the Co film at d = 1–2 Å has been observed. Resistance measurement of the Co film showed a fast decrease of the resistance down to some value limited by quantum-size effect in accordance with the formation of a two-dimensional Co phase at d = 1–2 Å.

K-shell spectra from Ag, Sn, Sm, Ta, and Au generated by intense femtosecond laser pulses

K-shell X-ray spectra were recorded by the Dual Crystal Spectrometer (DCS) from Ag, Sn, Sm, Ta, and Au planar foil targets irradiated by single intense femtosecond pulses from the Titan laser at Lawrence Livermore National Laboratory. DCS implements two quartz crystals in transmission (Laué) geometry covering the X-ray energy range 10–50 keV and 20–120 keV. The spectral images were recorded on photo-stimulable phosphor image plates and on film/phosphor cassettes. The Kα and Kβ spectral lines of Ag with energies 22 keV and 25 keV, Sn at 25 keV and 28 keV, Sm at 40 keV and 46 keV, Ta at 57 keV and 66 keV, and Au at 67 keV and 79 keV were clearly resolved. The observation of these spectral lines, resulting from 1s electron vacancies created by electrons with energies up to at least 80 keV, enables the implementation of K-shell spectroscopy diagnostic techniques for understanding the laser energy deposition, energetic electron generation, ionization distribution, and X-ray conversion efficiency in plasmas produced by an intense femtosecond laser pulse. Based on the measured energies of the Au K-shell transitions, we conclude that the observed Au K-shell transitions are from ionization stages lower than Au +44, and are most likely from neutral Au atoms, that the Titan plasmas and the hard X-ray emissions are dominated by electrons with energies exceeding 80 keV, and that thermal processes play a minor role.

Relaxation of slow highly charged ions hitting thin metallic foils

We developed a method to determine the relaxation time of the innermost vacancies for highly ionized heavy ions moving through the bulk. The method compares the intensities of photons emitted through the front and back sides of a thin metal foil. Using foils with known thickness and x-ray absorption cross sections, we directly obtained the mean x-ray emission depth, and thereafter the mean relaxation time. We present data for the emission depth of highly charged $8.5q$ keV and $23.5q$ keV ${\mathrm{Pb}}^{q+}$ ions $(q=53--58)$ impacting on thin Ta foils. The mean relaxation time of $M$-shell vacancies is estimated to be between 22 and $68\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$, depending on charge state of the projectile, which is about five times longer relaxation time than reported by Hattas et al. [Phys. Rev. Lett. 82, 4795 (1999)]. The experimental results are supported by a model calculation that combines molecular-orbital calculation for the ${\mathrm{Pb}}^{54+}\text{\ensuremath{-}}\mathrm{Ta}$ interaction system with a rate-equation model for inner-shell relaxation.

Dual, orthogonal, backlit pinhole radiography in OMEGA experiments

Backlit pinhole radiography used with ungated film as a detector creates x-ray radiographs with increased resolution and contrast. Current hydrodynamics experiments on the OMEGA Laser use a three-dimensional sinusoidal pattern as a seed perturbation for the study of instabilities. The structure of this perturbation makes it highly desirable to obtain two simultaneous orthogonal backlighting views. We accomplished this using two backlit pinholes each mounted 12mm from the target. The pinholes, of varying size and shape, were centered on 5mm square foils of 50μm thick Ta. The backlighting is by K-alpha emission from a 500μm square Ti or Sc foil mounted 500μm from the Ta on a plastic substrate. Four laser beams overfill the metal foil, so that the expanding plastic provides radial tamping of the expanding metal plasma. The resulting x-rays pass through the target onto (ungated) direct exposure film (DEF). Interference between the two views is reduced by using a nose cone in front of the DEF, typically with a 9mm Ta aperture and with magnets to deflect electrons. Comparison of varying types of pinholes and film exposures will be presented from recent experiments as well as an analysis of the background noise created using this experimental technique.

Analysis of impurities in high-purity aluminum oxide by glow discharge mass spectrometry

A method has been developed for determining trace components in high-purity aluminum oxide powder for making sapphire single crystals. The analyses have been performed with VG9000 glow-discharge mass spectrometer which provided a sensitivity at the sub-ppm level. To analyze nonconducting specimens, a secondary cathode made of high-purity Ta foil was employed. Effects have been determined from factors that influence the sensitivity. Mathematical simulation has been used in calculating the effects of molecular ions on the results. Isotopes are identified that provide the necessary analysis sensitivity and accuracy. The method allows one to distinguish impurities adsorbed on the particles from those that enter into the crystal lattice.

In situ synthesis and superconducting properties of MgB2 fibers

Superconducting MgB2 fibers are grown by a diffusion method, in which B filaments are exposed to Mg vapor inside a folded Ta foil over a wide range of temperature and growth time. The as-grown wires with a diameter of about 110μm are characterized by scanning electron microscopy and energy dispersive X-ray analysis. Surface morphology of the fibers turns out to be dependent on growth temperature and mixing ratio of Mg and B. Radial distribution of Mg ions into B is observed over the cross-sectional area. Transport properties of the MgB2 fibers are investigated in magnetic fields from 0 to 8T by use of a physical property measurement system. MgB2 fibers grown at 900°C for 2h show a superconducting transition at 38.1K with an onset temperature as 41.7K and ΔTc<3.03K. Resistance of the MgB2 fiber at room temperature is 4Ω and residual resistivity ratio (RRR) is estimated as 4.72. It is estimated that the upper critical field Hc2 at 4K is more than 16T. In addition, a small amount of magneto-resistance is detected at high magnetic fields.

Laser-driven flyer impact experiments at the LULI 2000 laser facility

New laser-driven flyer impact experiments have been performed at the LULI laboratory. In these experiments, three types of targets (single Al flyer, multi-layered, and foam-buffered high-Z metal) were used. Impacted conditions in fused quartz were measured with rear-side (two VISARs and SOP) and transverse diagnostics (shadowgraph). In the foam-buffered target, Ta foil was accelerated up to a velocity of 55 km/s. Shock wave accelerated in fused quartz by an Al flyer impact was generated, and the shock wave passing a distinct boundary to a conductive state was directly observed. This method is a way to create unique conditions within the EOS diagram of material.

Diffusion of 6Li in Ta and W

The objective of this work was the study of 6Li diffusion in the Ta and W refractory metals. The samples were prepared by ion implantation of 380keV 6Li+ ions into W and Ta thin foils (up to the fluence of 1016ions/cm2) and annealed up to the temperature 1940°C. The depth profiles of 6Li were determined using the Thermal Neutron Depth Profiling (TNDP) technique. The results showed that diffusion of 6Li in both W and Ta foils is very complex and cannot be described by simple Fick’s laws. Trapping centers (in the subsurface layers of both W and Ta metals) were supposed in a trial to explain the 6Li diffusion behaviour. However, the 6Li depth profiles were only partly explained. Other aspects are necessary to take into account for more proper quantification; such as spatially dependent diffusion coefficients, etc.

A Novel Mechanical Method to Measure Shear Strength in Specimens Under Pressure

ABSTRACTA new experimental apparatus has been developed for performing shear tests on specimens held under moderately high hydrostatic pressures (on the order of 4 GPa). This testing procedure experimentally determines the pressure-dependent shear strength of thin foil specimens. The experiments provide calibration data for models of materials subjected to extreme pressures such as the Steinberg-Guinan hardening model and can assist in model validation for discrete dislocation dynamics simulations, among others. This paper reports the development of the experimental procedures and the results of initial experiments on thin foils of polycrystalline Ta performed under hydrostatic pressures ranging from 1 to 4 GPa. Both yielding and hardening behavior of Ta are observed to be sensitive to the imposed pressure.

Corrosion behavior of magnetron sputtered α-Ta coatings on smooth and rough steel substrates

α-Ta coatings on smooth and rough steel substrates (AISI 4340) were studied in an effort to assess the resulting porosity and corrosion behavior. While the long-range crystallographic orientation of the coatings was found to be affected by the surface roughness, the short-range structure was invariant. Peak broadening in X-ray diffraction patterns attributed to microstrain and particle size was observed for coatings on both types of substrates as compared to Ta powder. Although the roughness was two orders of magnitude greater for the coatings deposited on the rough substrates than the smooth ones, the porosity was not significantly different. Furthermore, electrochemical impedance behavior over long exposure times of coatings deposited on smooth and rough steel substrates was similar to that of Ta foil. These results demonstrate that substrate roughness appears to have little to no effect on the coating quality with respect to corrosion performance for 50 μm coatings.

Laser polarization dependence of proton emission from a thin foil target irradiated by a 70fs, intense laser pulse

A study of proton emission from a 3-μm-thick Ta foil target irradiated by p-, s-, and circularly polarized laser pulses with respect to the target plane has been carried out. Protons with energies up to 880keV were observed in the target normal direction under the irradiation by the p-polarized laser pulse, which yielded the highest efficiency for proton emission. In contrast, s- and circularly polarized laser pulses gave the maximum energies of 610 and 680keV, respectively. The difference in the maximum energy between the p- and s-polarized cases was associated with the difference between the sheath fields estimated from electron spectra.

Corrosion behaviour of magnetron sputtered α- and β-Ta coatings on AISI 4340 steel as a function of coating thickness

The corrosion behaviour of magnetron sputtered α- and β-Ta coated AISI 4340 steels was studied with potentiodynamic polarization and electrochemical impedance spectroscopy. The coating porosity was observed to decrease with increasing coating thickness. For coatings less than 10 μm thick (α- or β-Ta), porosity was significant and open pores resulted in severe localized corrosion of the steel substrate, coating delamination, and overall coating failure. Additionally, the β-Ta coatings were more susceptible than the α-phase to delamination. As for the 50 and 100 μm thick α-Ta coatings, the electrochemical impedance behaviour was comparable to that of Ta foil, demonstrating the coating viability and corrosion resistance.