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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

EFFECT OF HIGH-ENERGY RESONANCES ON THE {sup 18}O(p, {alpha}){sup 15}N REACTION RATE AT AGB AND POST-AGB RELEVANT TEMPERATURES

The {sup 18}O(p, {alpha}){sup 15}N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as {sup 19}F, {sup 18}O, and {sup 15}N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by {alpha} radiative capture on {sup 15}N, which in turn is produced in the {sup 18}O proton-induced destruction. Peculiar {sup 18}O abundances are observed in R-Coronae Borealis stars, having {sup 16}O/{sup 18}O {approx}< 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the {sup 14}N/{sup 15}N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the {sup 18}O(p, {alpha}){sup 15}N reaction. In this work, a high accuracy {sup 18}O(p, {alpha}){sup 15}N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of {sup 19}F. In particular, we have focused on the study of the broad 660 keV 1/2{sup +} resonance corresponding to the 8.65 MeV level of {sup 19}F. Since {Gamma} {approx} 100-300 keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T {approx} 0.5 10{sup 9} K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1989

Line-of-sight effects on spectroscopic measurements in the inner solar wind region

The effect of the integration along the line of sight on the spectral line profiles of the resonantly scattered Lyman alpha radiation emitted by low-density coronal holes at heights above 1.5 Rs from sun center is investigated. It is shown how the spectral lines from this region are influenced by the Lyman alpha emission from surrounding regions with higher densities. The coronal hole and the surrounding areas are described by a two-fluid solar wind model. It is shown that the line-of-sight effects can be important for the interpretation of the Lyman alpha spectral line measurements in the outer corona and inner solar wind.

Esser, Ruth↗
NASA NTRS1990

The transfer of resonance-line radiation in static astrophysical media

An analytic solution is derived for the mean intensity of resonance-line radiation within an absorbing medium of large scattering optical depth but low density. The line profile, the mean number of scatterings before absorption or escape, the mean path length traveled, and the fraction of the photons which escape the medium are derived. Approximate methods are also developed which permit the treatment of media of intermediate optical depth, where scattering takes place in the Doppler core. Astrophysical applications include the absorption of H Ly-alpha radiation by stellar dust, the pumping of H2 Lyman band lines by H Ly-alpha and the Bowen fluorescence.

Neufeld, David A.↗
DOE OSTI2011

Simulation of the generation of characteristic X radiation under vacuum heating of electrons by a femtosecond laser pulse

An analytic model of the generation of characteristic X radiation under vacuum heating of electrons at the surface of a massive target by a p-polarized nonrelativistic femtosecond laser pulse is considered. The results of calculations satisfactorily describe the measured data on the output of K{sub {alpha}} radiation generated by laser pulses with a wavelength of 1.24 {mu}m and peak intensities of 5 Multiplication-Sign 10{sup 16}-2 Multiplication-Sign 10{sup 17} W/cm{sup 2}, incident at an angle of 45 Degree-Sign .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1994

Multiwavelength search for protoplanetary disks

Infrared emission of circumstellar dust was observed for almost one hundred T Tauri stars. This dust is interpreted to be part of a protoplanetary disk orbiting the central star. T Tauri stars are young stellar objects and evolve into solar type stars. Planets are believed to form in these disks. The spectral energy distribution of a disk depends on its temperature profile. Different disk regions emit at different wavelengths. The disk-star boundary layer is hot and emits H(alpha) radiation. Inner disk regions at around 1 AU with a temperature of a few hundred Kelvin can be probed in near infrared wavelength regimes. Outer disk regions at around 100 AU distance from the star are colder and emit far infrared and sub-millimeter radiation. Also, X-ray emission from the stellar surface can reveal information on disk properties. Emission from the stellar surface and the boundary layer may be shielded by circumstellar gas and dust. T Tauri stars with low H(alpha) emission, i.e. no boundary layer, show stronger X-ray emission than classical T Tauri stars, because the inner disk regions of weak emission-line T Tauri stars may be clear of material. In this paper, first ROSAT all sky survey results on the X-ray emission of T Tauri stars and correlations between X-ray luminosity and properties of T Tauri disks are presented. Due to atmospheric absorption, X-ray and most infrared observations cannot be carried out on Earth, but from Earth orbiting satellites (e.g. IRAS, ROSAT, ISO) or from lunar based observatories, which would have special advantages such as a stable environment.

Neuhaeuser, Ralph↗
DOE OSTI2025

Scintillation light detection in polycrystalline diamond using single photon detectors

Here, this study investigates the scintillation properties of polycrystalline diamond for particle detection applications, particularly in neutron and alpha radiation environments. Polycrystalline diamonds provide a cost-effective alternative to monocrystalline diamonds while retaining essential detection properties. Photoluminescence measurements were performed to analyze emission spectra, revealing distinct characteristics based on impurity content and crystallinity. Scintillation responses were assessed using Silicon Photomultipliers (SiPMs), demonstrating the capability of polycrystalline diamond powders to respond to alpha irradiation, albeit with reduced resolution compared to traditional scintillators. A prototype neutron detector was developed by combining diamond powder with neutron-sensitive 6 LiF, and its performance was evaluated through experimental testing and Geant4 simulations. The findings indicate that polycrystalline diamond-based detectors can achieve significant detection efficiency while remaining insensitive to gamma radiation, offering potential for portable neutron detection applications.

47 OTHER INSTRUMENTATION↗
DOE OSTI2010

The role of hot electron refluxing in laser-generated K-alpha sources

A study of the contribution of refluxing electrons in the production of K-alpha radiation from high-intensity laser irradiated thin targets has been performed. Thin copper foils both freestanding, and backed by a thick substrate were irradiated with laser pulses of energies around 100 J at intensities ranging from below 10{sup 17} to above 10{sup 19} W/cm{sup 2}. At high laser intensities we find a strong reduction in the K-alpha yield from targets backed by the substrate. The observed yield reduction is in good agreement with a simple model using hot electron spectra from particle-in-cell simulations or directly inferred from the measured bremsstrahlung emission and can therefore be interpreted as due to the suppression of hot electron refluxing. The study shows that refluxing electrons play a dominant role in high-intensity laser driven K- alpha generation and have to be taken into account in designing targets for laser driven high-flux K-alpha sources.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1983

H I Lyman-alpha in the sun - The effects of partial redistribution in the line wings

A form for the Lyman-alpha redistribution function that is modified to include the effects of collisional coupling between different energy states is presented. It is noted that this extends the work of Yelnik et al. (1981) and Roussel-Dupre(1982). By separating the source function into its primary components at all heights, the formation of Lyman-alpha radiation is investigated in detail. Frequencies in the line wing can be mapped back in such a way that the heights of formation for a change in lambda of plus or minus 0.5-6 A span the entire solar chromosphere. The usefulness of the Lyman-alpha wing as an atmospheric probe, however, is limited by long thermalization lengths, which result from almost coherent scattering outside of the Doppler core. When the line profiles calculated from the chromospheric models of Vernazza et al. (1981) are compared with the quiet-sun observations of Roussel-Dupre, agreement is found in integrated core intensities and in the line wing shape and normalized center-to-limb behavior. The calculated wing intensities, however, are a factor of four too small.

Roussel-Dupre, D.↗
DOE OSTI2013

INTERACTING GALACTIC NEUTRAL HYDROGEN FILAMENTS AND ASSOCIATED HIGH-FREQUENCY CONTINUUM EMISSION

Galactic H I emission profiles in an area where several large-scale filaments at velocities ranging from -46 km s{sup -1} to 0 km s{sup -1} overlap were decomposed into Gaussian components. Eighteen families of components defined by similarities of center velocity and line width were identified and related to small-scale structure in the high-frequency continuum emission observed by the Wilkinson Microwave Anisotropy Probe spacecraft, as evidenced in the Internal Linear Combination (ILC) map of Hinshaw et al. When the center velocities of the Gaussian families, which summarize the properties of all the H I along the lines of sight in a given area, are used to focus on H I channel maps the phenomenon of close associations between H I and ILC peaks reported in previous papers is dramatically highlighted. Of particular interest, each of two pairs of H I peaks straddles a continuum peak. The previously hypothesized model for producing the continuum radiation involving free-free emission from electrons is re-examined in light of the new data. By choosing reasonable values for the parameters required to evaluate the model, the distance for associated H I-ILC features is of order 30-100 pc. No associated H{alpha} radiation is expected because the electrons involved exist throughout the Milky Way. The mechanism for clumping and separation of neutrals and electrons needs to be explored. It is concluded that the small-scale ILC structure originates in the local interstellar medium and not at cosmological distances.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

Cometesimals in the inner solar system

Spectra obtained by the ultraviolet spectrometer on the Voyager 2 spacecraft between 1 and 2.5 AU are shown to provide evidence for a very large number of 'cometesimals' with radii between a few meters and a few tens of meters in the neighborhood of the earth. The evidence consists of a component in the interplanetary Lyman-alpha radiation that decreases rapidly with heliocentric distance. It is proposed that the source consists of cometesimals which are ice-coated, porous, low-density refractory boulders that may be the building blocks of ordinary comet nuclei. It is shown that the cometesimals required to produce the observed Lyman-alpha emission can also account for all the lunar craters with diameters between 200 m and 1500 m produced during the phase 3200 million years at sites such as Mare Tranquillitatis.

Donahue, T. M.↗
NASA NTRS1980

Radiative energy output of the 5 September 1973 flare

Measurements of the radiative energy output of the solar flare of Sept. 5, 1973, over a wavelength range of more than ten decades, from below 1 A to above 1 m are presented. Observations of soft X-rays (0.5-20 A), XUV and EUV lines (171-1863 A) and EUV continua (1400-1960 A), H alpha radiation, visible lines and continua (3700-8700 A) and radio emission (centimeter to meter wavelengths) were obtained concurrently by Skylab and ground-based instruments. Estimates of power output at flare maximum are obtained for the observed wavelengths with uncertainty of at least half an order of magnitude, due to corresponding uncertainties in EUV and visible fluxes. Taking into account energy radiated at unobserved wavelengths and the characteristic time of the best-reduced data (the soft X-ray), calculations indicate a total radiated flare energy of approximately 4 x 10 to the 29th erg.

Canfield, R. C.↗
NASA NTRS1983

Tentative confirmation of an aurora on Uranus

There have been three recent reports of the detection of Lyman-alpha radiation (due to atomic hydrogen, H, at wavelength 1,216 A) from Uranus by means of the International Ultraviolet Explorer (IUE) satellite. The interpretations of these results differ. Two reports conclude that there is a strong aurora on Uranus, but the third concludes that the source is resonance scattering of solar Lyman-alpha. This paper reports the detection of emission features due to molecular hydrogen, H2, near 1,600 A. This detection is near the limit of the IUE sensitivity. If it is real, the detection of H2 emission strongly supports the conclusion that Uranus has an aurora comparable in strength with those of the inner two giant planets, Jupiter and Saturn. The first published IUE spectra of the Saturn aurora are also presented.

Caldwell, J.↗
DOE OSTI2013

Exploring Graphene Field Effect Transistor Devices to Improve Spectral Resolution of Semiconductor Radiation Detectors

Graphene, a planar, atomically thin form of carbon, has unique electrical and material properties that could enable new high performance semiconductor devices. Graphene could be of specific interest in the development of room-temperature, high-resolution semiconductor radiation spectrometers. Incorporating graphene into a field-effect transistor architecture could provide an extremely high sensitivity readout mechanism for sensing charge carriers in a semiconductor detector, thus enabling the fabrication of a sensitive radiation sensor. In addition, the field effect transistor architecture allows us to sense only a single charge carrier type, such as electrons. This is an advantage for room-temperature semiconductor radiation detectors, which often suffer from significant hole trapping. Here we report on initial efforts towards device fabrication and proof-of-concept testing. This work investigates the use of graphene transferred onto silicon and silicon carbide, and the response of these fabricated graphene field effect transistor devices to stimuli such as light and alpha radiation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Development of radiopharmaceuticals for targeted alpha therapy: Where do we stand?

Targeted alpha therapy is an oncological treatment, where cytotoxic doses of alpha radiation are locally delivered to tumor cells, while the surrounding healthy tissue is minimally affected. This therapeutic strategy relies on radiopharmaceuticals made of medically relevant radionuclides chelated by ligands, and conjugated to targeting vectors, which promote the drug accumulation in tumor sites. This review discusses the state-of-the-art in the development of radiopharmaceuticals for targeted alpha therapy, breaking down their key structural components, such as radioisotope, targeting vector, and delivery formulation, and analyzing their pros and cons. Moreover, we discuss current drawbacks that are holding back targeted alpha therapy in the clinic, and identify ongoing strategies in field to overcome those issues, including radioisotope encapsulation in nanoformulations to prevent the release of the daughters. Lastly, we critically discuss potential opportunities the field holds, which may contribute to targeted alpha therapy becoming a gold standard treatment in oncology in the future.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2023

Development of local-power-free, remote α -particle detection using optical fibers

We demonstrate the application of fluorescence optical fiber coupled to a telecom grade fiber as a sensor for alpha particles using alpha-specific ZnS(Ag) scintillation materials whose wavelength is down-shifted into a low-loss region of the telecom grade fiber transmission band. Telecom-grade fiber optics offer a solution for sensing alpha radiation in deep repositories and cask storage for radioactive materials due to the stability of SiO 2 under normal environmental conditions and its relative radiation hardness at low radiation doses. Long-term nuclear waste storage facilities require sensors for the detection of leakage of radioactive materials that are maintenance-free, do not require power and can survive with no ‘wear out’ mechanisms for decades. By accomplishing the wavelength transformation, we maximize efficiencies in the detection of α-particles and signal transport and can detect alpha scintillation at distances on the order of >1 km with a sensor that is ~3% efficient and can be easily scaled as a sensor array. This paper describes the construction and testing of the sensor including manufacture of the controlled thickness films, verification of the wavelength shift from 450 to 620 nm and optimization of the sensitivity as a function of thickness. We also model the relative sensitivity of the film as a function of film thickness, and we demonstrate a signal-to-noise ratio of 10 at a range of greater than 1 km.

alpha particles↗
NASA NTRS1995

Composition/Structure/Dynamics of comet and planetary satellite atmospheres

This research program addresses two cases of tenuous planetary atmospheres: comets and Io. The comet atmospheric research seeks to analyze a set of spatial profiles of CN in comet Halley taken in a 7.4-day period in April 1986; to apply a new dust coma model to various observations; and to analyze observations of the inner hydrogen coma, which can be optically thick to the resonance scattering of Lyman-alpha radiation, with the newly developed approach that combines a spherical radiative transfer model with our Monte Carlo H coma model. The Io research seeks to understand the atmospheric escape from Io with a hybrid-kinetic model for neutral gases and plasma given methods and algorithms developed for the study of neutral gas cometary atmospheres and the earth's polar wind and plasmasphere. Progress is reported on cometary Hydrogen Lyman-alpha studies; time-series analysis of cometary spatial profiles; model analysis of the dust comae of comets; and a global kinetic atmospheric model of Io.

Combi, Michael R.↗
DOE OSTI2018

Self-healing effects in a semi-ordered liquid for stable electronic conversion of high-energy radiation

Radiation damage in solid-state semiconductors has, until now, placed strict limitations on the acceptable decay energies of radioisotopes in radiovoltaic cells. Relegation to low-energy beta-emitting isotopes has minimized the power output from these devices and limited the technology’s ability to deliver greater energy densities and longer lifetimes than conventional batteries. We demonstrate the self-healing abilities of a liquid-phase semiconducting alloy which can withstand high-energy alpha radiation. Neutron difraction of liquid selenium-sulfur shows the liquid phase repairing damage sustained in the irradiation of the solid phase. This self-healing behavior results in long-lived power output in a liquid selenium-sulfur alphavoltaic cell. To the best of our knowledge, this marks the only successful demonstration of resistance to high-energy radiation (>500keV) in a semiconducting material. This new robustness can potentially allow increases to the available energy density in radiovoltaic cells near 1000 times the current state of the art.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Note: Spatial resolution of Fuji BAS-TR and BAS-SR imaging plates

The spatial resolution of two types of imaging plates, Fuji BAS-TR and Fuji BAS-SR, has been measured using a knife-edge x-ray source of 8-keV Cu K{sub {alpha}} radiation. The values for the spatial resolution, defined as the distance between 10% and 90% levels of the edge spread function, are 94 {mu}m and 109 {mu}m, respectively. The resolution values are important for quantitative analysis of x-ray and particle imaging and spectroscopic diagnostics.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗