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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 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Mutual neutralization of atomic rare-gas cations (Ne{sup +}, Ar{sup +}, Kr{sup +}, Xe{sup +}) with atomic halide anions (Cl{sup −}, Br{sup −}, I{sup −})

We report thermal rate coefficients for 12 reactions of rare gas cations (Ne{sup +}, Ar{sup +}, Kr{sup +}, Xe{sup +}) with halide anions (Cl{sup −}, Br{sup −}, I{sup −}), comprising both mutual neutralization (MN) and transfer ionization. No rate coefficients have been previously reported for these reactions; however, the development of the Variable Electron and Neutral Density Attachment Mass Spectrometry technique makes it possible to measure the difference of the rate coefficients for pairs of parallel reactions in a Flowing Afterglow-Langmuir Probe apparatus. Measurements of 18 such combinations of competing reaction pairs yield an over-determined data set from which a consistent set of rate coefficients of the 12 MN reactions can be deduced. Unlike rate coefficients of MN reactions involving at least one polyatomic ion, which vary by at most a factor of ∼3, those of the atom-atom reactions vary by at least a factor 60 depending on the species. It is found that the rate coefficients involving light rare-gas ions are larger than those for the heavier rare-gas ions, but the opposite trend is observed in the progression from Cl{sup −} to I{sup −}. The largest rate coefficient is 6.5 × 10{sup −8} cm{sup 3} s{sup −1} for Ne{sup +} with I{sup −}. Rate coefficients for Ar{sup +}, Kr{sup +}, and Xe{sup +} reacting with Br{sub 2}{sup −} are also reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Tunable effective nonlinear refractive index of graphene dispersions during the distortion of spatial self-phase modulation

Spatial self-phase modulation (SSPM) was observed directly when a focused He-Ne laser beam at 633 nm went through liquid-phase-exfoliated graphene dispersions. The diffraction pattern of SSPM was found to be distorted rapidly right after the incident beam horizontally passing through the dispersions, while no distortion for the vertically incident geometry. We show that the distortion is originated mainly from the non-axis-symmetrical thermal convections of the graphene nanosheets induced by laser heating, and the relative change of nonlinear refractive index can be determined by the ratio of the distortion angle to the half-cone angle. Therefore, the effective nonlinear refractive index of graphene dispersions can be tuned by changing the incident intensity and the temperature of the dispersions.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Active target studies of the αp-process at CRIB

The αp-process is a sequence of (α, p)(p, γ) reactions important to the nuclear trajectory to higher masses in type I X-ray bursts. Specifically, the αp-process is schematically pure helium-burning, and thus unlike pure hydrogen-burning processes, does not require slow β{sup +} decays. Explosive helium burning is responsible for the observed short rise-times of X-ray bursts but ultimately gives way to the rp-process as the Coulomb barrier increases. Because the stellar reaction rates of these (α, p) reactions are poorly known over the relevant astrophysical energies, we performed systematic studies of the {sup 18}Ne(α,p), {sup 22}Mg(α,p) and {sup 30}S(α,p) reactions at the Center for Nuclear Study (CNS) low-energy radioactive ion beam separator, called CRIB. We produce the radioactive beams in-flight and scan the center-of-mass energy down into the Gamow Window using a thick target in inverse kinematics. The helium target gas also serves as part of the detector system, an active target, which was newly designed for these measurements. The active target, which uses gas electron multiplier (GEM) foils, allows for higher beam injection rates than previous multi-sampling and tracking proportional counters (MSTPC). We present a summary of our recent results from these active target experiments at CRIB.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Astrophysics studies relevant to stellar x-ray bursts

Two reactions of {sup 14}O(α,p){sup 17}F and {sup 18}Ne(α,p){sup 21}Na provide the pathways for breakout from the hot CNO cycles to the rp-process in type I X-ray bursts. To better determine their astrophysical reaction rates, resonance parameters of the compound nuclei {sup 18}Ne and {sup 22}Mg have been investigated by the resonant elastic scattering of {sup 17}F+p and {sup 21}Na+p, respectively. The {sup 17}F and {sup 21}Na radioactive ion beams were produced at the CNS Radioactive Ion Beam Separator and impinged on the thick proton targets. The excitation functions were obtained with a thick-target method over a wide excitation energy range. The resonance parameters in the compound nuclei {sup 18}Ne and {sup 22}Mg have been determined through an R-matrix analysis. New reaction rates of these two (α,p) reactions are recalculated. The astrophysical impact for the {sup 18}Ne(α,p){sup 21}Na reaction has been investigated through one-zone postprocessing X-ray burst calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

({sup 18}O,{sup 18}Ne) double charge-exchange with MAGNEX

An experimental study concerning Double Gamow-Teller (DGT) modes in ({sup 18}O,{sup 18}Ne) Double Charge-Exchange reactions has been very recently performed at INFN-LNS laboratory in Catania. The experiment was performed using a {sup 40}Ca solid target and a {sup 18}O Cyclotron beam at 270 MeV incident energy. Charged ejectiles produced in the reaction were momentum analyzed and identified by MAGNEX spectrometer at very forward angles. Preliminary results are presented in the present paper.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Exploring the {sup 22}Ne(p,γ){sup 23}Na reaction at LUNA and at HZDR

The {sup 22}Ne(p,γ){sup 23}Na reaction is involved in the hydrogen burning NeNa cycle. This determines the nucleosynthesis of the Ne and Na isotopes in the Red Giant Branch and Asymptotic Giant Branch phases of stellar evolution. In the energy range relevant for astrophysics (20 keV < E < 600 keV), the {sup 22}Ne(p,γ){sup 23}Na reaction rate is highly uncertain because of the contribution of a large number of resonances never measured directly. A related study is under preparation at the Laboratory for Underground Nuclear Astrophysics (LUNA), in the Gran Sasso National Laboratory, and it will cover the energy range 100 keV < E < 400 keV. Meanwhile, a measurement at higher energies (i.e. 436 keV) has been carried out at the Tandetron accelerator of the HZDR (Helmholtz Zentrum Dresden Rossendorf) in Germany. Some preliminary results will be presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

{sup 12}C+{sup 12}C reactions at astrophysical energies: Tests of targets behaviour under beam bombardment

{sup 12}C({sup 12}C,α){sup 20}Ne and {sup 12}C({sup 12}C,p){sup 23}Na are the most important reactions during the carbon burning phase in stars. Direct measurements at the relevant astrophysical energy (E=1.5±0.3MeV) are very challenging because of the extremely small cross sections involved and of the high beam-induced background originating from impurities in the targets. In addition, persistent resonant structures at low energies are not well understood and make the extrapolation of the cross section from high energy data very uncertain. As a preliminary step towards the measurements of the {sup 12}C({sup 12}C,α){sup 20}Ne and {sup 12}C({sup 12}C,p){sup 23}Na reactions we intend to investigate the behaviour of targets under beam bombardment, specifically the quantitative measurement of hydrogen and deuterium content of highly pure stable carbon targets in relation to target temperature. Experiments are taking place at the CIRCE accelerator in Caserta, Italy and preliminary results are presented here.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Radiation induced effects on mechanical properties of nanoporous gold foams

Previously, it was demonstrated that due to a high surface-to-volume ratio, nanoporous materials display radiation tolerance. The abundance of surfaces, which are perfect sinks for defects, and the relation between ligament size, defect diffusion, and time combine to define a window of radiation resistance [Fu et al., Appl. Phys. Lett. 101, 191607 (2012)]. Outside this window, the dominant defect created by irradiation in Au nanofoams are stacking fault tetrahedra (SFT). Molecular dynamics computer simulations of nanopillars, taken as the elemental constituent of foams, predict that SFTs act as dislocation sources inducing softening, in contrast to the usual behavior in bulk materials, where defects are obstacles to dislocation motion, producing hardening. In this work we test that prediction and answer the question whether irradiation actually hardens or softens a nanofam. Ne ion irradiations of gold nanofoams were performed at room temperature for a total dose up to 4 dpa, and their mechanical behavior was measured by nanoindentation. We observe that hardness increases after irradiation, a result that we analyze in terms of the role of SFTs on the deformation mode of foams.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Gamma ray measurements with photoconductive detectors using a dense plasma focus

Photons in the MeV range emitted from the dense plasma focus (DPF) at the NSTec North Las Vegas Facility have been measured with both neutron-damaged GaAs and natural diamond photoconductive detectors (PCDs). The DPF creates or “pinches” plasmas of various gases (e.g., H{sub 2}, D{sub 2}, Ne, Ar., etc.) that have enough energy to create MeV photons from either bremsstrahlung and/or (n,n{sup ′}) reactions if D{sub 2} gas is used. The high bandwidth of the PCDs enabled the first ever measurement of the fast micro-pinches present in DPF plasmas. Comparisons between a slower more conventional scintillator/photomultiplier tube based nuclear physics detectors were made to validate the response of the PCDs to fast intense MeV photon signals. Significant discrepancies in the diamond PCD responses were evident.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Investigation of complete and incomplete fusion dynamics of {sup 20}Ne induced reactions at energies above the Coulomb barrier

Experiment has been performed to explore the complete and incomplete fusion dynamics in heavy ion collisions using stacked foil activation technique. The measurement of excitation functions of the evaporation residues produced in the {sup 20}Ne+{sup 165}Ho system at projectile energies ranges ≈ 4-8 MeV/nucleon have been done. Measured cumulative and direct cross-sections have been compared with the theoretical model code PACE-2, which takes into account only the complete fusion process. The analysis indicates the presence of contributions from incomplete fusion processes in some α-emission channels following the break-up of the projectile {sup 20}Ne in the nuclear field of the target nucleus {sup 165}Ho.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The roles of the binodal curve and the spinodal curve in expansions from the supercritical state with flashing

Data extracted from time-of-flight (TOF) measurements made on steady-state He free jets at Göttingen already in 1986 and for pulsed Ne free jets investigated recently at Tel Aviv have been added to an earlier plot of terminal condensed-phase mass fraction x{sub 2∞} as a function of the dimensionless scaling parameter Γ. Γ characterizes the source (fluid species, temperature, pressure and throat diameter); values of x{sub 2∞} are extracted from TOF measurements using conservation of energy in the free-jet expansion. For nozzles consisting of an orifice in a thin plate; the extracted data yield 22 data points which are correlated satisfactorily by a single curve. The Ne free jets were expanded from a conical nozzle with a 20° half angle; the three extracted data points stand together but apart from the aforementioned curve, indicating that the presence of the conical wall influences significantly the expansion and hence the condensation. The 22 data points for the expansions via an orifice consist of 15 measurements with expansions from the gas-phase side of the binodal curve which crossed the binodal curve downstream from the sonic point and 7 measurements with expansions of the gas-phase product of the flashing which occurred after an expansion from the liquid-phase side of the binodal curve crossed the binodal curve upstream from the sonic point. The association of these 22 points with a single curve supports the alternating-phase model for flows with flashing upstream from the sonic point proposed earlier. In order to assess the role of the spinodal curve in such expansions, the spinodal curves for He and Ne were computed using general multi-parameter Helmholtz-free-energy equation-of-state formulations. Then, for the several sets of source-chamber conditions used in the free-jet measurements, thermodynamic states at key locations in the free-jet expansions (binodal curve, sonic point and spinodal curve) were evaluated, with the expansion presumed to be metastable from the binodal curve to the spinodal curve. TOF distributions with more than two peaks (interpreted earlier as superimposed alternating-state TOF distributions) indicated flashing of the metastable flow downstream from the binodal curve but upstream from the sonic point. This relatively early flashing is due apparently to destabilizing interactions with the walls of the source. If the expansion crosses the binodal curve downstream from the nozzle, the metastable fluid does not interact with surfaces and flashing might be delayed until the expansion reaches the spinodal curve. It is concluded that, if the expansion crosses the binodal curve before reaching the sonic point, the resulting metastable fluid downstream from the binodal curve interacts with the adjacent surfaces and flashes into liquid and vapor phases which expand alternately through the nozzle; the two associated alternating TOF distributions are superposed by the chopping process so that the result has the appearance of a single distribution with three peaks.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Interaction of the NO 3pπ (C {sup 2}Π) Rydberg state with RG (RG = Ne, Kr, and Xe): Potential energy surfaces and spectroscopy

We present new potential energy surfaces for the interaction of NO(C {sup 2}Π) with each of Ne, Kr, and Xe. The potential energy surfaces have been calculated using second order Møller-Plesset perturbation theory, exploiting a procedure to converge the reference Hartree-Fock wavefunction for the excited states: the maximum overlap method. The bound rovibrational states obtained from the surfaces are used to simulate the electronic spectra and their appearance is in good agreement with available (2+1) REMPI spectra. We discuss the assignment and appearance of these spectra, comparing to that of NO-Ar.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

High-resolution spectroscopy of jet-cooled CH{sub 5}{sup +}: Progress

Protonated methane (CH{sub 5}{sup +}) is thought to be a highly abundant molecular ion in interstellar medium, as well as a potentially bright μwave- mm wave emitter that could serve as a tracer for methane. This paper describes progress and first successful efforts to obtain a high resolution, supersonically cooled spectrum of CH{sub 5}{sup +} in the 2900-3100 cm{sup −1} region, formed in a slit supersonic discharge at low jet temperatures and with sub-Doppler resolution. Short term precision in frequency measurement (< 5 MHz on an hour time scale) is obtained from a thermally controlled optical transfer cavity servoloop locked onto a frequency stabilized HeNe laser. Long term precision (< 20 MHz day-to-day) due to pressure, temperature and humidity dependent index of refraction effects in the optical transfer cavity is also present and discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Basis convergence of range-separated density-functional theory

Range-separated density-functional theory (DFT) is an alternative approach to Kohn-Sham density-functional theory. The strategy of range-separated density-functional theory consists in separating the Coulomb electron-electron interaction into long-range and short-range components and treating the long-range part by an explicit many-body wave-function method and the short-range part by a density-functional approximation. Among the advantages of using many-body methods for the long-range part of the electron-electron interaction is that they are much less sensitive to the one-electron atomic basis compared to the case of the standard Coulomb interaction. Here, we provide a detailed study of the basis convergence of range-separated density-functional theory. We study the convergence of the partial-wave expansion of the long-range wave function near the electron-electron coalescence. We show that the rate of convergence is exponential with respect to the maximal angular momentum L for the long-range wave function, whereas it is polynomial for the case of the Coulomb interaction. We also study the convergence of the long-range second-order Møller-Plesset correlation energy of four systems (He, Ne, N{sub 2}, and H{sub 2}O) with cardinal number X of the Dunning basis sets cc − p(C)V XZ and find that the error in the correlation energy is best fitted by an exponential in X. This leads us to propose a three-point complete-basis-set extrapolation scheme for range-separated density-functional theory based on an exponential formula.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Peripheral elastic and inelastic scattering of {sup 17,18}O on light targets at 12 MeV/nucleon

The elastic and inelastic scattering of {sup 17,18}O with light targets has been undertaken at 12 MeV/nucleon in order to determine the optical potentials needed for the transfer reaction {sup 13}C({sup 17}O,{sup 18}O){sup 12}C. Optical potentials in both incoming and outgoing channels have been determined in a single experiment. This transfer reaction was used to infer the direct capture rate to the {sup 17}F(p,γ){sup 18}Ne which is essential to estimate the production of {sup 18}F at stellar energies in ONe novae. We demonstrate the stability of the ANC method and OMP results using good quality elastic and inelastic scattering data with stable beams. The peripherality of our reaction is inferred from a semiclassical decomposition of the total scattering amplitude into barrier and internal barrier components. Comparison between elastic scattering of {sup 17}O, {sup 18}O and {sup 16}O projectiles is made.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Prospects for the methods of radionuclide production

In the present report, methods of radionuclide production for the nuclear-medicine purposes are described. In a budget approach, the application of low-energy accelerators is especially advantageous. Intense flux of bremsstrahlung at electron accelerators or high-current cyclotron beams of alpha particles must supply a great yield for many isotopes. The choice of a target material and of the projectile energy provides enough variation for concrete species formation. The innovating procedures are here proposed for optimizing of methods, for instance, application of the noble-gas target for production and transport of activities. The known and new variants of the “generator” scheme are discussed. Many isotopes are listed as promising in the context of the therapeutic and theragnostic applications. Among them are isotopes/isomers emitting soft radiation for the selective and careful body treatment, also the positron emitters for PET, and the halogen and alkali-metal species convenient for chemical separation.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

Preparation of state purified beams of He, Ne, C, N, and O atoms

The production and guiding of ground state and metastable C, N, and O atoms in a two-meter-long, bent magnetic guide are described. Pure beams of metastable He({sup 3}S{sub 1}) and Ne({sup 3}P{sub 2}), and of ground state N({sup 4}S{sub 3/2}) and O({sup 3}P{sub 2}) are obtained using an Even-Lavie valve paired with a dielectric barrier discharge or electron bombardment source. Under these conditions no electronically excited C, N, or O atoms are observed at the exit of the guide. A general valve with electron impact excitation creates, in addition to ground state atoms, electronically excited C({sup 3}P{sub 2}; {sup 1}D{sub 2}) and N({sup 2}D{sub 5/2}; {sup 2}P{sub 3/2}) species. The two experimental conditions are complimentary, demonstrating the usefulness of a magnetic guide in crossed or merged beam experiments such as those described in Henson et al. [Science 338, 234 (2012)] and Jankunas et al. [J. Chem. Phys. 140, 244302 (2014)].

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗