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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Observation of the Λ ⁷He Hypernucleus by the (e, e'K⁺) Reaction

An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, He Λ ⁷, was observed for the first time with the (e, e'K⁺) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The He Λ ⁷ binding energy supplies the last missing information of the A=7, T=1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the ΛN potential.

Nakamura, S. N.↗
DOE OSTI2016

Search for light neutron-rich isotopes in stopped pion absorption

The results based on the spectroscopy of superheavy hydrogen isotopes ({sup 4−7}H), heavy helium isotopes ({sup 6,7}He), and heavy lithium isotopes ({sup 7−12}Li) produced in stopped pion absorption by light nuclei were analyzed. Search for nuclear states was performed in inclusive and correlation measurements of missing mass spectra. A broad range of excitation energies studied in correlation measurements provided the possibility of search for isobaric analog states and cluster resonances. A comparison with experimental and theoretical results of other authors was conducted.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Role of the tensor interaction in He isotopes with a tensor-optimized shell model

We studied the role of the tensor interaction in He isotopes systematically on the basis of the tensor-optimized shell model (TOSM). We use a bare nucleon-nucleon interaction AV8{sup '} obtained from nucleon-nucleon scattering data. The short-range correlation is treated in the unitary correlation operator method (UCOM). Using the TOSM + UCOM approach, we investigate the role of tensor interaction on each spectrum in He isotopes. It is found that the tensor interaction enhances the LS splitting energy observed in {sup 5}He, in which the p{sub 1/2} and p{sub 3/2} orbits play different roles on the tensor correlation. In {sup 6,7,8}He, the low-lying states containing extra neutrons in the p{sub 3/2} orbit gain the tensor contribution. On the other hand, the excited states containing extra neutrons in the p{sub 1/2} orbit lose the tensor contribution due to the Pauli-blocking effect with the 2p2h states in the {sup 4}He core configuration.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Tagged-weak {pi} method

A new 'tagged-weak {pi} method' is proposed for determination of electromagnetic transition probabilities B(E2) and B(M1) of the hypernuclear states with lifetimes of {approx}10{sup -10} s. With this method, we are planning to measure B(E2) and B(M1) for light hypernuclei at JLab. The results of Monte Carlo simulations for the case of E2(5/2{sup +}, 3/2{sup +} {yields} 1/2{sup +}) transitions in {sub {Lambda}}{sup 7}He hypernuclei are presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Measurements of the {sup 6}He+p resonant scattering

Measurements of the p({sup 6}He,p) elastic scattering excitation function have been performed in the RIBRAS system using a {sup 6}He secondary beam and a CH{sub 2} polyethylene thick target. The motivation is to observe states of the compound nucleus {sup 7}Li in the excitation energy range of E{sub exc}{sup 7Li} = 10.8-11.8MeV, where the isobaric analog state of {sup 7}He ground state lies. Excitation functions have been obtained at three laboratory angles θ{sub lab} = 0°, 20°, and 25° which correspond to θ{sub c.m} = 180°, 140°, and 130°.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Description of Continuum Spectrum States of Light Nuclei in the Shell Model

The SS-HORSE method is applied to describe the scattering of nucleons by light nuclei based on calculations within the No-Core Shell Model with JISP16 and Daejeon16 NN interactions. The resonant states in {sup 5}He, {sup 5}Li, and {sup 7}He nuclei have been investigated. The SS-HORSE method generalized to the case of the democratic decay is also applied to study a four-neutron system (tetraneutron). The calculations with JISP16 and Daejeon16 and with chiral NN interactions indicate the existence of a rather narrow low-energy tetraneutron resonance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Feasibility of line-ratio spectroscopy on helium and neon as edge diagnostic tool for Wendelstein 7-X

A beam emission spectroscopy system on thermal helium (He) and neon (Ne) has been set up at Wendelstein 7-X to measure edge electron temperature and density profiles utilizing the line-ratio technique or its extension by the analysis of absolutely calibrated line emissions. The setup for a first systematic test of these techniques of quantitative atomic spectroscopy in the limiter startup phase (OP1.1) is reported together with first measured profiles. Lastly, this setup and the first results are an important test for developing the technique for the upcoming high density, low temperature island divertor regime.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Trapping helium in Y{sub 2}Ti{sub 2}O{sub 7} compared to in matrix iron: A first principles study

Pyrochlore Y{sub 2}Ti{sub 2}O{sub 7} is a primary precipitate phase in nano-structured ferritic alloys (NFAs) for fission and fusion energy applications. We report a theoretical study for assessing the relative stability of trapping helium in Y{sub 2}Ti{sub 2}O{sub 7} versus in matrix iron. Various defect structures and the associated energies are examined and compared. Results reveal that helium can be deeply trapped in Y{sub 2}Ti{sub 2}O{sub 7} and that the corresponding self-interaction is essentially repulsive. Transmutant helium in NFAs prefers to occupy individual octa-interstitial sites in Y{sub 2}Ti{sub 2}O{sub 7}, before forming small clusters in Y{sub 2}Ti{sub 2}O{sub 7}. Helium partitioning in NFAs depends on the number and dispersion of Y{sub 2}Ti{sub 2}O{sub 7}; and thus initially, bubble formation and growth in iron matrix can be largely suppressed. Charge transfer occurs from helium to neighboring oxygen anions, but not to neighboring metal cations, suggesting a general effectiveness of trapping helium in oxides. Reasons for the ultimate fate of helium to form small nm-scale interface bubbles are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Measurements of plasma parameters in the divertor island of Wendelstein 7-X through line-ratio spectroscopy on helium

We report electron temperature T e and density n e have been measured in the divertor island of Wendelstein 7-X by means of a new thermal He-beam system utilizing line-ratio spectroscopy. This system is equipped with a poloidal arrangement of five gas valves that allows to infer 2D plasma profiles T e ( R,Z ) and n e ( R,Z ) across the magnetic island forming the island divertor. A local maximum in T e ( R,Z ) was measured along the flux surfaces located between the island center and the outer separatrix. In the island center, characterized by closed field lines, a clear local minimum in T e was measured, indicating that no direct heat deposition occurs in this region and that the perpendicular heat flux from the core plasma into this domain is small. Increasing the island size leads to a reduction of the connection length in the scrape-off layer (SOL) and to a shift of the island center towards the divertor target. In this scenario, the T e ( R,Z ) are reduced in the entire island domain. Density profiles are found flat across the divertor island for both island size scenarios. These findings are supported by similar observations made with a reciprocating probe plunging through the same SOL island at the mid-plane of W7-X representing the upstream position in this 3D divertor geometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

First principles assessment of helium trapping in Y{sub 2}TiO{sub 5} in nano-featured ferritic alloys

Nano-scale Y{sub 2}Ti{sub 2}O{sub 7} and Y{sub 2}TiO{sub 5} oxides are the major features that provide high strength and irradiation tolerance in nano-structured ferritic alloys. Here, we employ density functional theory to study helium trapping in Y{sub 2}TiO{sub 5}. The results suggest that helium is more deeply trapped in Y{sub 2}TiO{sub 5} compared to Y{sub 2}Ti{sub 2}O{sub 7}. Helium occupies open channels in Y{sub 2}TiO{sub 5}, where it weakly chemically interacts with neighboring oxygen anions, and results in less volume expansion compared to Y{sub 2}Ti{sub 2}O{sub 7}, reducing strains in the iron matrix. The corresponding helium mobility in these channels is very high. While its ultimate fate is to form oxide/matrix interface bubbles, transient deep trapping of helium in oxides plays a major role in the ability of NFA to manage helium distribution.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Hypernuclear no-core shell model

We extend the No-Core Shell Model (NCSM) methodology to incorporate strangeness degrees of freedom and apply it to single-Λ hypernuclei. After discussing the transformation of the hyperon-nucleon (YN) interaction into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group transformation applied to it to improve model-space convergence, we introduce two complementary formulations of the NCSM, one that uses relative Jacobi coordinates and symmetry-adapted basis states to fully exploit the symmetries of the hypernuclear Hamiltonian, and one working in a Slater determinant basis of HO states where antisymmetrization and computation of matrix elements is simple and to which an importance-truncation scheme can be applied. For the Jacobi-coordinate formulation, we give an iterative procedure for the construction of the antisymmetric basis for arbitrary particle number and present the formulae used to embed two- and three-baryon interactions into the many-body space. For the Slater-determinant formulation, we report on the conversion of the YN interaction matrix elements from relative to single-particle coordinates, the importance-truncation scheme that tailors the model space to the description of the low-lying spectrum, and the role of the redundant center-of-mass degrees of freedom. We end with a confirmation of both formulations in the four-body system, giving converged ground-state energies for a chiral Hamiltonian, and present a short survey of the A ≤ 7 hyper-helium isotopes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

The RaDIATE High-Energy Proton Materials Irradiation Experiment at the Brookhaven Linac Isotope Producer Facility

The RaDIATE collaboration (Radiation Damage In Accelerator Target Environments) was founded in 2012 to bring together the high-energy accelerator target and nuclear materials communities to address the challenging issue of radiation damage effects in beam-intercepting materials. Success of current and future high intensity accelerator target facilities requires a fundamental understanding of these effects including measurement of materials property data. Toward this goal, the RaDIATE collaboration organized and carried out a materials irradiation run at the Brookhaven Linac Isotope Producer facility (BLIP). The experiment utilized a 181 MeV proton beam to irradiate several capsules, each containing many candidate material samples for various accelerator components. Materials included various grades/alloys of beryllium, graphite, silicon, iridium, titanium, TZM, CuCrZr, and aluminum. Attainable peak damage from an 8-week irradiation run ranges from 0.03 DPA (Be) to 7 DPA (Ir). Helium production is expected to range from 5 appm/DPA (Ir) to 3,000 appm/DPA (Be). The motivation, experimental parameters, as well as the post-irradiation examination plans of this experiment are described.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Characterizing the recovery of a solid surface after tungsten nano-tendril formation

Here, recovery of a flat tungsten surface from a nano-tendril surface is attempted through three techniques; a mechanical wipe, a 1673 K annealing, and laser-induced thermal transients. Results were determined through SEM imaging and elastic recoil detection to assess the helium content in the surface. The mechanical wipe leaves a ~0.5 μm deep layer of nano-tendrils on the surface post-wipe regardless of the initial nano-tendril layer depth. Laser-induced thermal transients only significantly impact the surface morphology at heat loads of 35.2 MJ/m 2 s 1/2 or above, however a fully flat or recovered surface was not achieved for 100 transients at this heat load despite reducing the helium content by a factor of ~7. A 1673 K annealing removes all detectable levels of helium but sub-surface voids/bubbles remain intact. The surface is recovered to a nearly flat state with only some remnants of nano-tendrils re-integrating into the surface remaining.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2011

THE INTEGRATION OF PROCESS HEAT APPLICATIONS TO HIGH TEMPERATURE GAS REACTORS

A high temperature gas reactor, HTGR, can produce industrial process steam, high-temperature heat-transfer gases, and/or electricity. In conventional industrial processes, these products are generated by the combustion of fossil fuels such as coal and natural gas, resulting in significant emissions of greenhouse gases such as carbon dioxide. Heat or electricity produced in an HTGR could be used to supply process heat or electricity to conventional processes without generating any greenhouse gases. Process heat from a reactor needs to be transported by a gas to the industrial process. Two such gases were considered in this study: helium and steam. For this analysis, it was assumed that steam was delivered at 17 MPa and 540 C and helium was delivered at 7 MPa and at a variety of temperatures. The temperature of the gas returning from the industrial process and going to the HTGR must be within certain temperature ranges to maintain the correct reactor inlet temperature for a particular reactor outlet temperature. The returning gas may be below the reactor inlet temperature, ROT, but not above. The optimal return temperature produces the maximum process heat gas flow rate. For steam, the delivered pressure sets an optimal reactor outlet temperature based on the condensation temperature of the steam. ROTs greater than 769.7 C produce no additional advantage for the production of steam.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2025

Vertical column dual-comb spectroscopy to a TBS

Open-path dual-frequency-comb spectroscopy (DCS) is a broadband, high spectral resolution, and high precision method for measuring gas concentrations over kilometer-scale paths. It has been used for detection and quantification of emissions of pollutants, hazardous gasses, and greenhouse gasses (GHGs). DCS has been shown to measure trace-gas mixing ratios with 0.14%-0.4% agreement between instruments. To achieve high signal-to-noise ratios (SNRs) with DCS, comb light is targeted onto a retroreflector at the end of the measurement path, which returns the signal to a detector co-located with the launch signal. Installing the retroreflector on a mobile platform such as a balloon or unmanned aerial vehicle (UAV) extends the capabilities of DCS by enabling variable path lengths, greater mobility, and access to higher altitudes. Mobile-target DCS has many uses in plume and leak detection, emissions modeling, and planetary boundary layer (PBL) studies. It is a promising method for observing vertical distributions of GHGs and mixing processes in the PBL, which are difficult to measure but important for pollution and climate monitoring as well as for understanding transport of gasses through the atmosphere. Tethered balloons are an intriguing platform because they enable longer flight durations and higher altitudes than easily obtainable with a UAV and thus allow for column measurements up to and above the PBL. New measurements completed in October/November 2024 reach the highest altitudes above ground level yet achieved by mobile-target DCS. For these measurements, the retroreflector was mounted on a 7 m diameter tethered helium balloon. An actively tracking gimbal on the ground holds the DCS launch telescope and keeps the 5 cm beam pointed onto the retroreflector while the balloon is lifted, lowered, and moved by wind and turbulence.

atmosphere↗
DOE OSTI2010

Role of interfaces i nthe design of ultra-high strength, radiation damage tolerant nanocomposites

The combination of high strength and high radiation damage tolerance in nanolaminate composites can be achieved when the individual layers in these composites are only a few nanometers thick and contain special interfaces that act both as obstacles to slip, as well as sinks for radiation-induced defects. The morphological and phase stabilities and strength and ductility of these nano-composites under ion irradiation are explored as a function of layer thickness, temperature and interface structure. Magnetron sputtered metallic multilayers such as Cu-Nb and V-Ag with a range of individual layer thickness from approximately 2 nm to 50 nm and the corresponding 1000 nm thick single layer films were implanted with helium ions at room temperature. Cross-sectional Transmission Electron Microscopy (TEM) was used to measure the distribution of helium bubbles and correlated with the helium concentration profile measured vis ion beam analysis techniques to obtain the helium concentration at which bubbles are detected in TEM. It was found that in multilayers the minimum helium concentration to form bubbles (approximately I nm in size) that are easily resolved in through-focus TEM imaging was several atomic %, orders of magnitude higher than that in single layer metal films. This observation is consistent with an increased solubility of helium at interfaces that is predicted by atomistic modeling of the atomic structures of fcc-bcc interfaces. At helium concentrations as high as 7 at.%, a uniform distribution of I nm diameter bubbles results in negligible irradiation hardening and loss of deformability in multi layers with layer thicknesses of a few nanometers. The control of atomic structures of interfaces to produce high helium solubility at interfaces is crucial in the design of nano-composite materials that are radiation damage tolerant. Reduced radiation damage also leads to a reduction in the irradiation hardening, particularly at layer thickness of approximately 5 run and below. The strategies for design of radiation-tolerant structural materials based on the knowledge gained from this work will be discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Study of the structure of light, unstable nuclei and the mechanism of elastic proton scattering

The review presents calculations of elastic p {sup 6}He-, p {sup 8}Li-, p {sup 9}Li- and p {sup 9}C scattering in the framework of the Glauber theory of multiple diffraction scattering at intermediate energies of 70 and 700 MeV/nucleon. The most significant result of the calculations is that we have utilized realistic three-body wave functions obtained within modern nuclear models. The relation is found between differential cross sections and intercluster potentials, where the nuclear wave functions are calculated. Conclusions are made concerning the types of potentials which describe most realistically the available experimental data. The method for calculation of three-body wave functions in α-n-n-, α-t-n-, {sup 7}Be-p-p-, α-t-2n-, and {sup 7}Li-n-n models is described with discussion of inter-cluster potentials and the quantum-number configurations taken into consideration. It is revealed how the wave functions and the nuclear electromagnetic characteristics calculated using these wave functions depend on the choice of intercluster potentials. The derivation of matrix elements (amplitudes) of pA scattering in the framework of the Glauber approach with three-body wave functions is presented by an example of {sup 6}He nucleus. Discussing the results of calculation of differential cross sections and the analyzing power (A{sub y}), we established how the calculated characteristics depend on a wave-function structure and dynamics of the process determined by a Glauber operator of multiple scattering. The calculated differential cross sections and analyzing powers are compared with available experimental data and calculations by other authors performed for different formalisms, which allows us to make justified conclusions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

TYPE Ib/c SUPERNOVAE IN BINARY SYSTEMS. I. EVOLUTION AND PROPERTIES OF THE PROGENITOR STARS

We investigate the evolution of Type Ib/c supernova (SN Ib/c) progenitors in close binary systems, using new evolutionary models that include the effects of rotation, with initial masses of 12-25 M{sub sun} for the primary components, and of single helium stars with initial masses of 2.8-20 M{sub sun}. We find that, despite the impact of tidal interaction on the rotation of primary stars, the amount of angular momentum retained in the core at the presupernova stage in different binary model sequences converges to a value similar to those found in previous single star models. This amount is large enough to produce millisecond pulsars, but too small to produce magnetars or long gamma-ray bursts. We employ the most up-to-date estimate for the Wolf-Rayet mass-loss rate, and its implications for SN Ib/c progenitors are discussed in detail. In terms of stellar structure, SN Ib/c progenitors in binary systems at solar metallicity are predicted to have a wide range of final masses up to about 7 M{sub sun}, with helium envelopes of M{sub He} {approx_equal} 0.16-1.5 M{sub sun}. Our results indicate that, if the lack of helium lines in the spectra of SNe Ic were due to small amounts of helium (e.g., M{sub He} {approx}< 0.5), the distribution of both initial and final masses of SN Ic progenitors should be bimodal. Furthermore, we find that a thin hydrogen layer (0.001 M{sub sun} {approx}< M{sub H} {approx}< 0.01 M{sub sun}) is expected to be present in many SN Ib progenitors at the presupernova stage. We show that the presence of hydrogen, together with a rather thick helium envelope, can lead to a significant expansion of some SN Ib/c progenitors by the time of supernova explosion. This may have important consequences for the shock break-out and supernova light curve. We also argue that some SN progenitors with thin hydrogen layers produced via Case AB/B transfer might be related to Type IIb supernova progenitors with relatively small radii of about 10 R{sub sun}.

79 ASTRONOMY AND ASTROPHYSICS↗