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At least 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Study of 1–8 keV K-α x-ray emission from high intensity femtosecond laser produced plasma

We report an experimental study on the optimization of a laser plasma based x-ray source of ultra-short duration K-α line radiation. The interaction of pulses from a CPA based Ti:sapphire laser (10 TW, 45 fs, 10 Hz) system with magnesium, titanium, iron and copper solid target generates bright 1-8 keV K-α x-ray radiation. The x-ray yield was optimized with the laser pulse duration (at fixed fluence) which is varied in the range of 45 fs to 1.4 ps. It showed a maximum at laser pulse duration of ∼740 fs, 420 fs, 350 and 250 fs for Mg (1.3 keV), Ti (4.5 keV), Fe (6.4 keV) and Cu (8.05 keV) respectively. The x-ray yield is observed to be independent of the sign of the chirp. The scaling of the K-α yield (I{sub x} ∝ I{sub L}{sup β}) for 45 fs and optimized pulse duration were measured for laser intensities in the region of 3 × 10{sup 14} – 8 × 10{sup 17}. The x-ray yield shows a much faster scaling exponent β = 1.5, 2.1, 2.4 and 2.6 for Mg, Ti, Fe and Cu respectively at optimized pulse duration compared to scaling exponent of 0.65, 1.3, 1.5, and 1.7 obtained for 45 fs duration laser pulses. The laser to x-ray energy conversion efficiencies obtained for different target materials are η{sub Mg} = 1.2 × 10{sup −5}, η{sub Ti} = 3.1 × 10{sup −5}, η{sub Fe} = 2.7 × 10{sup −5}, η{sub Cu} = 1.9 × 10{sup −5}. The results have been explained from the efficient generation of optimal energy hot electrons at longer laser pulse duration. The faster scaling observed at optimal pulse duration indicates that the x-ray source is generated at the target surface and saturation of x-ray emission would appear at larger laser fluence. An example of utilization of the source for measurement of shock-wave profiles in a silicon crystal by time resolved x-ray diffraction is also presented.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Positive temperature coefficient of coercivity in Sm{sub 1−x}Dy{sub x}(Co{sub 0.695}Fe{sub 0.2}Cu{sub 0.08}Zr{sub 0.025}){sub 7.2} magnets with spin-reorientation-transition cell boundary phases

Positive temperature coefficients of coercivity are first obtained in the series of Sm{sub 1−x}Dy{sub x} (Co{sub 0.695}Fe{sub 0.2}Cu{sub 0.08}Zr{sub 0.025}){sub 7.2} magnets. The temperature range with a positive temperature coefficient of coercivity is gradually moving to higher temperature with the increase of x. Thermal magnetic analysis shows a spin reorientation transition of cell boundary phase in these magnets. It is interesting to find the abnormal coercivity is controlled by the spin-reorientation-transition cell boundary phases, and the spin reorientation temperature of cell boundary phase is consisted with the start point of the temperature range with abnormal behavior. The different temperature coefficients are discussed in terms of a nucleation model.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Exchange spring in A1/L1{sub 0} FePt composite and its application in magnetic force microscope

This paper reported fabrication of Fe{sub x}Pt{sub 100-x} films with (001) epitaxy on MgO(100) substrates. The atomic percentage of Fe was changed within the range of x = 10–85 in order to search the optimal atomic ratio for achieving both high and isotropic-like coercivity. It was found that the Fe{sub 60}Pt{sub 40} film exhibited large coercivities exceeding 5 kOe along both in-plane and out-of-plane directions due to the formation of A1/L1{sub 0} FePt composite. A penta-domain model for hard/soft/hard exchange spring system was proposed to interpret the anomalous magnetization behaviors observed in Fe{sub 60}Pt{sub 40} sample. By using Fe{sub 60}Pt{sub 40} as the magnetic coating layer on a probe of magnetic force microscope, the flux changes at a linear density of 1000 kfci could be readily observed at a resolution of ∼13 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Antiparallel interface coupling evidenced by negative rotatable anisotropy in IrMn/NiFe bilayers

Negative rotatable anisotropy is estimated via ferromagnetic resonance measurements in as-made, annealed, and ion-irradiated IrMn{sub 3}/Ni{sub 81}Fe{sub 19} bilayers. Opposite to previous observations, inverse correlation between rotatable anisotropy and coercivity is observed. The exchange-bias field, determined from hysteresis loop measurements, is higher than that obtained from ferromagnetic resonance for all samples. The results are discussed in terms of majority antiparallel coupling and magnetic-field-induced transitions from antiparallel to parallel states of uncompensated spins at ferromagnet/antiferromagnet interface. We affirm that an observation of negative rotatable anisotropy evidences antiparallel coupling even in systems presenting conventional exchange bias.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Tunable configurational anisotropy in collective magnetization dynamics of Ni{sub 80}Fe{sub 20} nanodot arrays with varying dot shapes

We present broadband ferromagnetic resonance measurements of tunable spin wave anisotropy in arrays of nanodots with different dot shapes. Magnetization dynamics of the circular dot array shows two modes, while square, diamond, and triangular dot arrays show three, three, and four modes, respectively. Various distinct rotational symmetries in the configurational anisotropy of the nanodot arrays are observed with the variation of dot shape. The observed spin wave modes are reproduced by micromagnetic simulations and the calculated mode profiles show different collective modes determined by internal and stray magnetic fields. Effects of dot shapes are observed in combination with the effects of lattice symmetry and the shape of the boundary of the array. The collective behaviour is observed to be weakest in the diamond shaped dots and strongest in circular shaped dots. This is further confirmed by the stray field calculation. The large variation of spin wave mode frequencies and their configurational anisotropies with dot shapes are important for selection of suitable basis structures for future magnonic crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Co{sub 2}FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

We succeed to integrate BaO as a tunneling barrier into Co{sub 2}FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co{sub 2}FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Current-driven antivortex core resonance measured by the rectifying effect

We demonstrate the current-driven resonance of a single antivortex core confined in a cross-shaped Ni{sub 81}Fe{sub 19} wire. The antivortex core dynamics can be excited purely by spin transfer torque; therefore, it is significant to understand the current-induced magnetization dynamics. The antivortex core resonance can be measured from the frequency dependence of a rectified voltage generated by an alternating current application. We found that the resonance frequency and peak amplitude greatly depend on the external magnetic field. This result is in good agreement with micromagnetic simulation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structures and magnetic properties of iron silicide from adaptive genetic algorithm and first-principles calculations

We performed a systematic search for low-energy structures of binary iron silicide over a wide range of compositions using the crystal structure prediction method based on adaptive genetic algorithm. 36 structures with formation energies within 50 meV/atom (11 of them are within 20 meV) above the convex hull formed by experimentally known stable structures are predicted. Magnetic properties of these low-energy structures are investigated. Some of these structures can be promising candidates for rare-earth-free permanent magnet.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Measurement of integrated flux of cosmic ray muons at sea level using the INO-ICAL prototype detector

The India-based Neutrino Observatory (INO) collaboration is planning to set-up a magnetized Iron-CALorimeter (ICAL) to study atmospheric neutrino oscillations with precise measurements of oscillations parameters. The ICAL uses 50 kton iron as target mass and about 28800 Resistive Plate Chambers (RPC) of 2 m × 2 m in area as active detector elements. As part of its R and D program, a prototype detector stack comprising 12 layers of RPCs of 1 m × 1 m in area has been set-up at Tata Institute of Fundamental Research (TIFR) to study the detector parameters using cosmic ray muons. We present here a study of muon flux measurement at sea level and lower latitude. (Site latitude: 18°54'N, longitude: 72°48'E.)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Violation of the rule of parsimony: Mixed local moment and itinerant Fe magnetism in Fe 3 GeN

Ternary iron nitrides are of considerable interest due to their diverse magnetic properties. We find, based on first principles calculations, that the relatively minor structural distortion from the cubic antiperovskite structure in Fe$_3$GeN, consisting of octahedral rotations, leads to unusual magnetic behavior. In particular, there is a separation into Fe sites with very different magnetic behaviors, specifically a site with Fe atoms having a stable local moment and a site where the Fe shows characteristics of much more itinerant behavior. This shows a remarkable flexibility of the Fe magnetic behavior in these nitrides and points towards the possibility of systems where minor structural and chemical changes can lead to dramatic changes in magnetic properties. The results suggest that, analogously to oxide perovskite materials, modulation of magnetic properties via chemical or strain control of octahedral rotation may be feasible. Furthermore, this may then lead to approaches for tuning magnetism to realize properties of interest, for example tuning magnetic transitions to quantum critical regimes or to proximity to metamagnetic transitions of interest for devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Muon–hadron detector of the carpet-2 array

The 1-GeV muon–hadron detector of the Carpet-2 multipurpose shower array at the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences (INR, Moscow, Russia) is able to record simultaneously muons and hadrons. The procedure developed for this device makes it possible to separate the muon and hadron components to a high degree of precision. The spatial and energy features of the muon and hadron extensive-air-shower components are presented. Experimental data from the Carpet-2 array are contrasted against data from the EAS-TOP and KASCADE arrays and against the results of the calculations based on the CORSIKA (GHEISHA + QGSJET01) code package and performed for primary protons and iron nuclei.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1974

Thermomagnetic analysis of meteorites. I - Cl chondrites

Samples of all five of the known Cl chondrites have been analyzed thermomagnetically. The only magnetic phase found in four of the chondrites (Alais, Ivuna, Orgueil, Tonk) was magnetite containing less than 6% nickel. The Revelstoke Cl chondrite contains essentially Ni-free Fe3O4 as the predominant phase; however, a small amount of a thermally unstable iron compound (presumably FeS) is additionally present. Estimates of the weight percentage of magnetite, based on saturation moments, are: Alais, 5.3 plus or minus 0.4%; Ivuna, 12.2 plus or minus 0.9%; Orgueil, 11.9 plus or minus 0.8%; Revelstoke, 7.2 plus or minus 0.5%; and Tonk, 9.4 plus or minus 0.6%.

Larson, E. E.↗
NASA NTRSDate not supplied

Coupling of Dust Mineralogy to Radiation in NASA GISS ModelE: Impact Upon Dust Optical Properties and Direct Radiative Effect

Estimates of dust direct radiative effect (DRE) are still largely uncertain mainly due to the poor constraining of regional variations of dust absorption, whose known connection with mineral composition is still largely neglected by most Earth System Models. The inaccurate knowledge of soil mineralogy and insufficient measurements of dust physical and optical properties still present the main challenges for a proper representation of the dust-radiation interaction in climate models. We recently upgraded the coupling of dust minerals to shortwave radiation in the NASA GISS ModelE. In particular, we extended the interaction to online-calculated minerals and implemented two different mixing configurations: i) external mixing of three main mineral components and ii) internal mixing of all minerals, allowing a dynamic fraction of iron oxides. We used a semi-empirical approach for the optical calculations, mostly based on aerosol chamber measurements from natural soils, aiming to reduce the influence of uncertain assumptions on the optical properties and mixing state of individual minerals. In this contribution, we present the results of our first calculations of dust optical properties and DREs based on different mixing configurations of interactive minerals. We show the changes to dust optical depth and single scattering albedo, with respect to the control case using homogeneous dust composition, and the consequent global and regional variations in dust DREs at the top of atmosphere and at surface. We also compare the model optical properties with AERONET data, filtered to identify dust scenes. We find that accounting for the diverse properties of dust minerals modifies the pattern of regional dust absorption and therefore its impact upon climate. We also show that the mineralogy effect is sensitive to the assumed mixing state of minerals.

dust direct radiative effect↗
DOE OSTI2013

Hiereachical Bayesian Model for Combining Geochemical and Geophysical Data for Environmental Applications Software

Development of a hierarchical Bayesian model to estimate the spatiotemporal distribution of aqueous geochemical parameters associated with in-situ bioremediation using surface spectral induced polarization (SIP) data and borehole geochemical measurements collected during a bioremediation experiment at a uranium-contaminated site near Rifle, Colorado. The SIP data are first inverted for Cole-Cole parameters including chargeability, time constant, resistivity at the DC frequency and dependence factor, at each pixel of two-dimensional grids using a previously developed stochastic method. Correlations between the inverted Cole-Cole parameters and the wellbore-based groundwater chemistry measurements indicative of key metabolic processes within the aquifer (e.g. ferrous iron, sulfate, uranium) were established and used as a basis for petrophysical model development. The developed Bayesian model consists of three levels of statistical sub-models: 1) data model, providing links between geochemical and geophysical attributes, 2) process model, describing the spatial and temporal variability of geochemical properties in the subsurface system, and 3) parameter model, describing prior distributions of various parameters and initial conditions. The unknown parameters are estimated using Markov chain Monte Carlo methods. By combining the temporally distributed geochemical data with the spatially distributed geophysical data, we obtain the spatio-temporal distribution of ferrous iron, sulfate and sulfide, and their associated uncertainity information. The obtained results can be used to assess the efficacy of the bioremediation treatment over space and time and to constrain reactive transport models.

Chen, Jinsong↗
DOE OSTI2016

Alloying effect of niobium and tin on the zirconium alloy fuel cladding behavior at high temperature oxidation in steam - 2016-0072

As the materials for fuel claddings for water-cooled reactors, binary and multicomponent zirconium alloys zirconium-niobium (Zr-Nb) (E110, M5), zirconium-tin-iron (Zr-Sn-Fe) (Zircaloy-2,-4), and zirconium-niobium-tin-iron (Zr-Nb-Sn-Fe) (E635, ZIRLO{sup R} ) most commonly are used. Improvement extends, in particular, by varying their composition by niobium, tin, and iron. At the same time, importance is given to ensuring the safe operation of the fuel rods not only in normal conditions but also in emergency situations such as a loss of coolant accident. In this paper, we present the research results of studies of the influence of alloying elements niobium, tin, and iron on corrosion resistance and embrittlement at high-temperature steam oxidation of fuel claddings based on the alloy types Zr-xNb (x=1.0/2.5) and Zr-xNb-ySn-zFe (x=0.6/2.4; y=0.24/1.1; z=0.18/0.34) made by using zirconium sponge. We conducted high-temperature steam oxidation tests at temperatures of 1,000 deg. C, 1,100 deg. C, and 1,200 deg. C with continuous measurement of the weight gain during the experiment and subsequent cooling in steam with rate ∼ 20 deg. C/s. We conducted studies of kinetics of high-temperature oxidation in steam, structural-phase state changes, alloying elements distribution, absorbed hydrogen content, and residual ductility after rapid cooling of the oxidized specimens. We revealed the difference in the oxidation kinetics of the materials studied, which decreased as the oxidation temperature increased. Likewise, an increase of the tin content in the alloy influenced a specimen's breakaway oxidation intensification at 1,000 deg. C. This shows that the mechanical properties of fuel claddings oxidized under the same conditions depend on their alloying composition, and the hydrogen fraction is absorbed by the specimen and formed by the oxidation of ZrO{sub 2}, α-Zr(O), and ex-β layer structures, which in turn varies depending on the alloy composition. The increase of niobium, tin, and iron content in the zirconium alloy leads to a decrease in the residual ductility of fuel claddings after high-temperature steam oxidation. According to obtained results, among the materials studied, Zr-1.0Nb alloy is the most resistant to embrittlement during high-temperature steam oxidation at temperatures of 1,000-1,200 deg. C. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2019

Methodologies for Evaluation of Corrosion Protection for Ductile Iron Pipe

Repairing the nation’s infrastructure and ensuring its future durability are key issues facing the United States. It is important that these critical issues are addressed with appropriate and economical solutions based on the best modern scientific information. For example, in 2013 the American Society of Civil Engineers (ASCE), in its Report Card for America’s Infrastructure, gave the state of the critical water/wastewater infrastructure an overall grade of “D.” According to the ASCE, 6 billion gallons of drinking water disappear every day, mostly due to leaks in old pipes. Corrosion of water pipes plays a role in their durability and, for external pipe corrosion, the corrosivity of soils varies by location and is based on several factors, including soil resistivity. There is universal agreement that water pipes require some type of corrosion mitigation strategy (i.e., bare pipe is not installed). However, in specifying which strategy to employ for ductile iron pipe (DIP) in different soil types, the recommendations of the US Bureau of Reclamation (USBR) Technical Memorandum 8140-CC-2004-1 were subject to considerable debate. So much so that in 2009, this report was the subject of a study by the National Academy, which did not resolve the debate about the most effective and affordable solutions. Zinc-coatings have been explored in other parts of the world. Despite being widely used in Europe for almost 60 years, zinc coating was barely mentioned in either the 2004 or 2009 studies, which appeared to focus on North American data.

36 MATERIALS SCIENCE↗
DOE OSTI2016

TU-H-BRA-05: A System Design for Integration of An Interior MRI and a Linear Accelerator

Purpose: MRI is a highly desirable modality to guide radiation therapy but it is difficult to combine a conventional MRI scanner directly with a linear accelerator (linac). An interior MRI (iMRI) concept has been proposed to acquire MRI images within a small field of view only covering targets and immediate surrounding tissues. The objective of this project is to design an interior MRI system to work with a linac using a magnet to provide a field around 0.2T in a cube of 20cm per side, and perform image reconstruction with a slightly inhomogeneous static magnetic fields. Methods: All the results are simulated using a commercially available software package, FARADY. In our design, a ring structure holds the iMRI system and also imbeds a linac treatment head. The ring is synchronized to the linac gantry rotation. Half of the ring is made of steel and becomes a magnetic flux return path (yoke) so that a strong magnetic field will be limited inside the iron circuit and fringe fields will be very weak. In order to increase the static magnetic field homogeneity, special steel magnet boots or tips were simulated. Three curved boots were designed based on two-dimensional curves: arc, parabola and hyperbola. Results: Different boot surfaces modify magnetic field distributions differently. With the same pair of neodymium-iron-boron (NdFeB) magnets, the magnetic induction at the centers are 0.217T, 0.201T, 0.204T, and 0.212T for flat, arc, parabola and hyperbola boots, respectively. The hyperbola boots lead to the most homogeneous results, the static magnetic field deviations are within 0.5% in a cube of 20cm, and can be further improved using shimming techniques. Conclusion: This study supports the concept of an iMRI design. Successful development of iMRI will provide crucial information for tumor delineation in radiation therapy.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Mössbauer Spectral Properties of Yttrium Iron Garnet, Y3Fe5O12, and its Isovalent and Nonisovalent Yttrium-Substituted Solid Solutions

Several high-resolution Mössbauer spectra of yttrium iron garnet, Y3Fe5O12, have been fit as a function of temperature with a new model based on a detailed analysis of the spectral changes that result from a reduction from the cubic Ia–3d space group to the trigonal R–3 space group. These spectral fits, which are all statistically identical, indicate that the magnetic sextet arising from the 16a site in cubic symmetry is subdivided into three sextets arising from the 6f, and the 3d, 3d, and the 1a, 1b, and 2c sites in rhombohedral-axis trigonal symmetry. The 24d site in cubic symmetry is subdivided into four sextets arising from four different 6f sites in R–3 rhombohedral-axis trigonal symmetry, sites that differ only by the angles between the principal axis of the electric field gradient tensor and the magnetic hyperfine field assumed to be parallel with the magnetic easy axis. This analysis, when applied to the potential nuclear waste storage compounds, Y3-xCa0.5xTh0.5xFe5O12 and Y3- xCa0.5xCe0.5xFe5O12, indicates virtually no perturbation of the structural, electronic, and magnetic properties upon substitution of small amounts of calcium(II) and thorium(IV) or cerium(IV) onto the yttrium(III) 24c site as compared with Y3Fe5O12. The observed broadening of the four different 6f sites derived from the 24d site results from the substitution of yttrium(III) by calcium(II) and thorium(IV) or cerium(IV) cations on the next-nearest neighbor 24c site. In contrast, the same analysis, when applied to Y2.8Ce0.2Fe5O12, indicates a local perturbation of the magnetic exchange pathways as a result of the presence of cerium(IV) in the 24c next-nearest neighbor site of the iron(III) 24d site.

Environmental Molecular Sciences Laboratory↗