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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Monochromatic Minibeams Radiotherapy: From Healthy Tissue-Sparing Effect Studies Toward First Experimental Glioma Bearing Rats Therapy

Purpose: The purpose of this study was to evaluate high-dose single fraction delivered with monochromatic X-rays minibeams for the radiotherapy of primary brain tumors in rats. Methods and Materials: Two groups of healthy rats were irradiated with one anteroposterior minibeam incidence (four minibeams, 123 Gy prescribed dose at 1 cm depth in the brain) or two interleaved incidences (54 Gy prescribed dose in a 5 Multiplication-Sign 5 Multiplication-Sign 4.8 mm{sup 3} volume centered in the right hemisphere), respectively. Magnetic resonance imaging (MRI) follow-up was performed over 1 year. T2-weighted (T2w) images, apparent diffusion coefficient (ADC), and blood vessel permeability maps were acquired. F98 tumor bearing rats were also irradiated with interleaved minibeams to achieve a homogeneous dose of 54 Gy delivered to an 8 Multiplication-Sign 8 Multiplication-Sign 7.8 mm{sup 3} volume centered on the tumor. Anatomic and functional MRI follow-up was performed every 10 days after irradiation. T2w images, ADC, and perfusion maps were acquired. Results: All healthy rats were euthanized 1 year after irradiation without any clinical alteration visible by simple examination. T2w and ADC measurements remain stable for the single incidence irradiation group. Localized Gd-DOTA permeability, however, was observed 9 months after irradiation for the interleaved incidences group. The survival time of irradiated glioma bearing rats was significantly longer than that of untreated animals (49 {+-} 12.5 days versus 23.3 {+-} 2 days, p < 0.001). The tumoral cerebral blood flow and blood volume tend to decrease after irradiation. Conclusions: This study demonstrates the sparing effect of minibeams on healthy tissue. The increased life span achieved for irradiated glioma bearing rats was similar to the one obtained with other radiotherapy techniques. This experimental tumor therapy study shows the feasibility of using X-ray minibeams with high doses in brain tumor radiotherapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Crystal growth and electronic structure of low-temperature phase SrMgF{sub 4}

Using the vertical Bridgman method, the single crystal of low temperature phase SrMgF{sub 4} is obtained. The crystal is in a very good optical quality with the size of 10×7×5 mm{sup 3}. Detailed photoemission spectra of the element core levels are determined by a monochromatic AlKa (1486.6 eV) X-ray source. Moreover, the first-principles calculations are performed to investigate the electronic structure of SrMgF{sub 4}. A good agreement between experimental and calculated results is achieved. It is demonstrated that almost all the electronic orbitals are strongly localized and the hybridization with the others is very small, but the Mg–F bonds covalency is relatively stronger than that of Sr–F bonds. - Graphical abstract: Large size of low-temperature phase SrMgF{sub 4} crystal was obtained (right) and its electronic structure was investigated by X-ray photoelectron spectroscopy and first-principles calculation (left). - Highlights: • Large size single crystal of low-temperature phase SrMgF{sub 4} is obtained. • Electronic structure of SrMgF{sub 4} is measured by X-ray photoelectron spectroscopy. • Partial densities of states are determined by first-principles calculation. • Good agreement between experimental and calculated results is achieved. • Strong ionic characteristics of chemical bonds are exhibited in SrMgF{sub 4}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

An in situ study of resin-assisted solvothermal metal-organic framework synthesis

A newly developed in situ monochromatic high-energy X-ray diffraction setup was used to investigate the synthesis of MOFs using cation-impregnated polymer resin beads as a ion source. The Co–NDC–DMF (NDC=2,6-naphthalenedicarboxylate; DMF=dimethylformamide) system was investigated, a system which is known to produce at least three distinct frameworks. It was found that the resin-assisted synthesis results in the preferential formation of a topology previously impossible to synthesise in bulk, while the comparable nitrate-salt synthesis appeared to form an alternative phases. It was also found that the resin-assisted synthesis is highly diffusion-controlled. - Graphical abstract: In situ monochromatic high-energy X-ray diffraction study of a MOF synthesis. - Highlights: • Resin-assisted solvothermal MOF synthesis was studied using in situ diffraction. • Full kinetics of reaction can be obtained from in situ data. • Kinetics show that this resin-assisted synthesis is diffusion controlled. • Resin-assisted synthesis enables the production of an alternative bulk phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Photoelectrochemical properties of electrostatically self-assembled multilayer films formed by three bipolar hemicyanines and H{sub 4}SiW{sub 12}O{sub 40}

Graphical abstract: Display Omitted Highlight: ► Three self-assembled films of hemicyanines of and H{sub 4}SiW{sub 12}O{sub 40}. ► Uniformly deposited multilayers with reversible electrochemical activity. ► Large cathodic photocurrent densities of 0.36–1.02 μA/cm{sup 2} with IPCE of 0.75–0.98%. -- Abstract: The electrostatically self-assembled multilayer films of three bipolar hemicyanines with varied alkyl chain lengths were prepared by alternating adsorption of H{sub 4}SiW{sub 12}O{sub 40} and these hemicyanines, and characterized by UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and cyclic voltammetry. The results showed that these inorganic–organic composite films were uniformly deposited with good electrochemical activity. Photoelectrochemical investigations showed that the films exhibited large cathodic photocurrent densities of 0.36–1.02 μA/cm{sup 2} with the monochromatic incident photon-to-electron conversion efficiency of 0.75–0.98% while irradiated with 100 mW/cm{sup 2} polychromatic light (730 nm > λ > 325 nm) at an applied potential of −0.2 V vs. saturated calomel electrode, being strongly dependent on the alkyl chain lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Diamond X-ray photodiode for white and monochromatic SR beams

High-purity, single-crystal CVD diamond plates are screened for quality and instrumented into a sensor assembly for quantitative characterization of flux and position sensitivity. Initial investigations have yielded encouraging results and have led to further development. Several limiting complications are observed and discussed, as well as mitigations thereof. For example, diamond quality requirements for X-ray diodes include low nitrogen impurity and crystallographic defectivity. Thin electrode windows and electronic readout performance are ultimately also critical to device performance. Promising features observed so far from prototype devices include calculable responsivity, flux linearity, position sensitivity and timing performance. Recent results from testing in high-flux and high-speed applications are described.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Equilibrium velocity distributions in parallel propagating low-frequency Alfvenic turbulence

The equilibrium velocity distributions in parallel propagating, circularly polarized low-frequency Alfvenic turbulence are presented. The equilibrium solutions of the monochromatic Alfven waves are extended to those of incompressible Alfvenic turbulence with the broadband spectrum in low beta plasmas. It is shown that the ''apparent temperature'' due to the nonresonant ion heating is explained on the basis of the equilibrium velocity distribution. The anisotropic equilibrium velocity distribution corresponding to Alfvenic turbulence in the Chew-Goldberger-Low system is also demonstrated. It is suggested that the distribution can be the back ground structure in the asymmetric velocity distributions observed in the solar wind.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Note: Binding energy scale calibration of electron spectrometers for photoelectron spectroscopy using a single sample

The feasibility of calibrating the binding energy scale for photoelectron spectroscopy using a single sample without sputter cleaning was investigated. By measuring the Fermi level of a Au film with both monochromatic Al K{alpha} (h{nu}= 1486.7 eV) and He I{alpha} (h{nu}= 21.22 eV), the binding energy scale was simply and accurately calibrated. This method is found to yield binding energy values for the Cu 2p{sub 3/2}, Ag 3d{sub 5/2}, and Au 4f{sub 7/2} peaks that agree with the standard tabulated values defined in International Organization for Standardization 15472 to within {+-}0.02 eV.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

Gas dynamic effects on formation of carbon dimers in laser-produced plasmas

We investigated the effect of helium and nitrogen pressures on the dynamics of molecular species formation during laser ablation of carbon. For producing plasmas, planar carbon targets were irradiated with 1064 nm, 6 ns pulses from an Nd:yttrium aluminum garnet laser. The emission from excited C{sub 2} and CN molecules was studied using space resolved optical time-of-flight emission spectroscopy and spectrally resolved fast imaging. The intensity oscillations in C{sub 2} and CN monochromatic fast imaging and their emission space-time contours suggest that recombination is the major mechanism of C{sub 2} formation within the laser ablation carbon plumes in the presence of ambient gas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

In situ observation of x-ray irradiation effect by using a multiwave x-ray diffraction phenomenon

In situ observation of the complex scattering amplitude of x-ray specular reflection (amplitude reflectivity) was performed by using a method with a multiwave x-ray diffraction phenomenon. The method can be applied to the noncrystalline layers on a single crystal and allows us to determine its amplitude reflectivity with only a 0.01 degree of crystal rotation, that is, the area irradiated by the incident x rays is almost unchanged during the measurement. We used this method to observe an irradiation effect induced by monochromatic synchrotron x-rays that occurred on a Si(001) single crystal covered with a native oxide layer. The obtained time evolution of the amplitude reflectivities exhibited counterclockwise behavior in the complex plane, indicating that the thickness of the noncrystalline layer on the crystalline substrate was increased by the irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Poynting vector, energy densities, and pressure of collective transverse electromagnetic fluctuations in unmagnetized plasmas

A systematic calculation of the electromagnetic properties (Poynting vector, electromagnetic energy, and pressure) of the collective transverse fluctuations in unmagnetized plasmas with velocity-anisotropic plasma particle distributions functions is presented. Time-averaged electromagnetic properties for monochromatic weakly damped wave-like fluctuations and space-averaged electromagnetic properties for monochromatic weakly propagating and aperiodic fluctuations are calculated. For aperiodic fluctuations, the Poynting vector as well as the sum of the space-averaged electric and magnetic field energy densities vanish. However, aperiodic fluctuations possess a positive pressure given by its magnetic energy density. This finite pressure density p{sub a} of aperiodic fluctuations has important consequences for the dynamics of cosmic unmagnetized plasmas such as the intergalactic medium after reionization. Adopting the standard cosmological evolution model, we show that this additional pressure changes the expansion law of the universe leading to further deceleration. Negative vacuum pressure counterbalances this deceleration to an accelerating universe provided that the negative vacuum pressure is greater than 1.5p{sub a}, which we estimate to be of the order 2.1 {center_dot} 10{sup -16} dyn cm{sup -2}.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Asymmetric-cut variable-incident-angle monochromator

A novel asymmetric-cut variable-incident-angle monochromator was constructed and tested in 1997 at the Advanced Photon Source of Argonne National Laboratory. The monochromator was originally designed as a high heat load monochromator capable of handling 5-10 kW beams from a wiggler source. This was accomplished by spreading the x-ray beam out on the surface an asymmetric-cut crystal and by using liquid metal cooling of the first crystal. The monochromator turned out to be a highly versatile monochromator that could perform many different types of experiments. The monochromator consisted of two 18 deg. asymmetrically cut Si crystals that could be rotated about 3 independent axes. The first stage ({Phi}) rotates the crystal around an axis perpendicular to the diffraction plane. This rotation changes the angle of the incident beam with the surface of the crystal without changing the Bragg angle. The second rotation ({Psi}) is perpendicular to the first and is used to control the shape of the beam footprint on the crystal. The third rotation ({Theta}) controls the Bragg angle. Besides the high heat load application, the use of asymmetrically cut crystals allows one to increase or decrease the acceptance angle for crystal diffraction of a monochromatic x-ray beam and allows one to increase or decrease the wavelength bandwidth of the diffraction of a continuum source like a bending-magnet beam or a normal x-ray-tube source. When the monochromator is used in the doubly expanding mode, it is possible to expand the vertical size of the double-diffracted beam by a factor of 10-15. When this was combined with a bending magnet source, it was possible to generate an 8 keV area beam, 16 mm wide by 26 mm high with a uniform intensity and parallel to 1.2 arc sec that could be applied in imaging experiments.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Solid liner implosions on Z for producing multi-megabar, shockless compressions

Current pulse shaping techniques, originally developed for planar dynamic material experiments on the Z-machine [M. K. Matzen et al., Phys. Plasmas 12, 055503 (2005)], are adapted to the design of controlled cylindrical liner implosions. By driving these targets with a current pulse shape that prevents shock formation inside the liner, shock heating is avoided along with the corresponding decrease in electrical conductivity ahead of the magnetic diffusion wave penetrating the liner. This results in an imploding liner with a significant amount of its mass in the solid phase and at multi-megabar pressures. Pressures in the solid region of a shaped pulse driven beryllium liner fielded on the Z-machine are inferred to 5.5 Mbar, while simulations suggest implosion velocities greater than 50kms{sup -1}. These solid liner experiments are diagnosed with multi-frame monochromatic x-ray backlighting which is used to infer the material density and pressure. This work has led to a new platform on the Z-machine that can be used to perform off-Hugoniot measurements at higher pressures than are accessible through magnetically driven planar geometries.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Interfacial oxide re-growth in thin film metal oxide III-V semiconductor systems

The Al{sub 2}O{sub 3}/GaAs and HfO{sub 2}/GaAs interfaces after atomic layer deposition are studied using in situ monochromatic x-ray photoelectron spectroscopy. Samples are deliberately exposed to atmospheric conditions and interfacial oxide re-growth is observed. The extent of this re-growth is found to depend on the dielectric material and the exposure temperature. Comparisons with previous studies show that ex situ characterization can result in misleading conclusions about the interface reactions occurring during the metal oxide deposition process.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Fast microtomography using bright monochromatic x-rays

A fast microtomography system for high-resolution high-speed imaging has been developed using bright monochromatic x-rays at the BL29XU beamline of SPring-8. The shortest scan time for microtomography we attained was 0.25 s in 1.25 {mu}m effective pixel size by combining the bright monochromatic x-rays, a fast rotating sample stage, and a high performance x-ray imaging detector. The feasibility of the tomography system was successfully demonstrated by visualization of rising bubbles in a viscous liquid, an interesting issue in multiphase flow physics. This system also provides a high spatial (a measurable feature size of 300 nm) or a very high temporal (9.8 {mu}s) resolution in radiographs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Quasi-monochromatic field-emission x-ray source

By favoring the L-peak emission over the bremsstrahlung part, direct quasi-monochromatic soft x-ray emission has been obtained with a field emission (FE) x-ray source. The electron impact x-ray setup uses an arrayed cathode of carbon nanopearl FE tips as a stable cold electron source within a vacuum of 10{sup -6}-10{sup -7} Torr. The high brightness of the FE e-beam coupled with the array structure of the cold cathode allows a smoother control of the x-ray emission intensity. The wavelength of the x-ray source can be modified by the choice of target materials. Using Mo as the target material, the x-ray emission shows a peak centered at 2.45 keV with a monochromaticity between 75% and 55% and a FWHM in the range of 450 eV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Energy distribution measurement of narrow-band ultrashort x-ray beams via K-edge filters subtraction

The characterization of novel x-ray sources includes the measurement of the photon flux and the energy distribution of the produced beam. The aim of BEATS2 experiment at the SPARC-LAB facility of the INFN National Laboratories of Frascati (Rome, Italy) is to investigate possible medical applications of an x-ray source based on Thomson relativistic back-scattering. This source is expected to produce a pulsed quasi-monochromatic x-ray beam with an instantaneous flux of 10{sup 20} ph/s in pulses 10 ps long and with an average energy of about 20 keV. A direct measurement of energy distribution of this beam is very difficult with traditional detectors because of the extremely high photon flux. In this paper, we present a method for the evaluation of the energy distribution of quasi-monochromatic x-ray beams based on beam filtration with K-edge absorbing foils in the energy range of interest (16-22 keV). The technique was tested measuring the energy distribution of an x-ray beam having a spectrum similar to the expected one (SPARC-LAB Thomson source) by using a tungsten anode x-ray tube properly filtered and powered. The energy distribution obtained has been compared with the one measured with a HPGe detector showing very good agreement.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Proton induced quasi-monochromatic x-ray beams for soft x-ray spectroscopy studies and selective x-ray fluorescence analysis

We present the analytical features and performance of an x-ray spectroscopy end station of moderate energy resolution operating with proton-induced quasi-monochromatic x-ray beams. The apparatus was designed, installed and operated at the 5.5 MV Tandem VdG Accelerator Laboratory of the Institute of Nuclear Physics, N.C.S.R. 'Demokritos,' Athens. The setup includes a two-level ultrahigh vacuum chamber that hosts in the lower level up to six primary targets in a rotatable holder; there, the irradiation of pure element materials-used as primary targets-with few-MeV high current ({approx}{mu}A) proton beams produces intense quasi-monochromatic x-ray beams of selectable energy. In the chamber's upper level, a six-position rotatable sample holder hosts the targets considered for x-ray spectroscopy studies. The proton-induced x-ray beam, after proper collimation, is guided to the sample position whereas various filters can be also inserted along the beam's path to eliminate the backscattered protons or/and to absorb selectively components of the x-ray beam. The apparatus incorporates an ultrathin window Si(Li) spectrometer (FWHM 136 eV at 5.89 keV) coupled with low-noise electronics capable of efficiently detecting photons down to carbon K{alpha}. Exemplary soft x-ray spectroscopy studies and results of selective x-ray fluorescence analysis are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Investigation of an ion-ion hybrid Alfven wave resonator

A theoretical and experimental investigation is made of a wave resonator based on the concept of wave reflection along the confinement magnetic field at a spatial location where the wave frequency matches the local value of the ion-ion hybrid frequency. Such a situation can be realized by shear Alfven waves in a magnetized plasma with two ion species because this mode has zero parallel group velocity and experiences a cut-off at the ion-ion hybrid frequency. Since the ion-ion hybrid frequency is proportional to the magnetic field, it is expected that a magnetic well configuration in a two-ion plasma can result in an Alfven wave resonator. Such a concept has been proposed in various space plasma studies and could have relevance to mirror and tokamak fusion devices. This study demonstrates such a resonator in a controlled laboratory experiment using a H{sup +}-He{sup +} mixture. The resonator response is investigated by launching monochromatic waves and impulses from a magnetic loop antenna. The observed frequency spectra are found to agree with predictions of a theoretical model of trapped eigenmodes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗