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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Population inversion mechanisms producing nuclear lasing in He-3-Ar, Xe, Kr, Cl, and UF6

The paper examines the lasing excitation mechanisms of present nuclear lasers, with a view to developing more efficient, higher power nuclear lasers. Particular attention is given to volumetric nuclear discharges pumped by either the He-3(n, p)H-3 reaction or the U-235F6(n, ff)FF reaction. Insight gained from these laser systems will make it possible to determine the major excitation mechanisms and then to look for new gaseous laser systems where these excitation mechanisms dominate.

Deyoung, R. J.↗
NASA NTRS1983

Cosmic-ray abundances of Sn, Te, Xe, and Ba nuclei measured on HEAO 3

The results of an analysis of HEAO 3 Heavy Nuclei Experimental data covering 440 days of observations of Sn-Ba nuclei in cosmic rays are reported. The particles were detected by a Cernkov counter, and a Z-squared ceiling was calculated to normalize the histograms produced. The observed large abundance of Sn and Ba relative to other elements in the region of interest indicated a predominance of the s-process in the source of the particles. When account was taken of first ionization potential effects, the data indicated that the material could be solar system in origin. A source dominated by the r-process nucleosynthesis was ruled out at the 0.93 confidence level.

Binns, W. R.↗
NASA NTRS1983

The relative abundances of Sn, Te, Xe, Ba and Ce

Elements with even atomic number (Z) in the interval 50 or = Z or = 58 were resolved in the cosmic radiation using the Heavy Nuclei Experiment on the HEAO-3 satellite. Their relative abundances were compared with the results expected from pure r-process material, pure s-process material, and solar system material, both with and without a modification due to possible first ionization potential effects. Such effects may be the result of the preferential acceleration, and hence enhancement in the cosmic rays, of those elements having low first ionization potentials. Measurements were found to be inconsistent with pure r-process material at the greater than 98% confidence level whether or not the first ionization potential adjustments are made.

Krombel, K. E.↗
NASA NTRS1983

I-Xe studies of individual Allende chondrules

Nine Allende chondrules and a sample of oxidized Allende matrix material are subjected to iodine-xenon studies, and the model compositions derived are compared with those of the Bjurbole chondrules. Chondrule 6 yields a well-defined isochron, with an apparent age that is later than Bjurbole whole rock. Elemental abundances suggest that all the chondrules except 6 may be pyroxene- or mesostasis-rich. The oxidized matrix sample gives a well defined isochron with an initial I-129/I-127 ratio higher than any plateaus seen in the chondrules, suggesting that the matrix predates the chondrules.

Swindle, T. D.↗
NASA NTRS1985

Interactions of heavy nuclei, Kr, Xe and Ho, in light targets

Over the past few years, the HEAO-3 measurements of the abundance of ultra-heavy cosmic ray nuclei (Z 26) at Earth were analyzed. In order to interpret these abundances in terms of a source composition, allowances must be made for the propagation of the nuclei in the interstellar medium. Vital to any calculation of the propagation is a knowlege of the total and partial interaction cross sections for these heavy nuclei on hydrogen. Until recently, data on such reactions have been scarce. The semi-empirical formalism of Silberberg and Tsao were relied upon to predict the partial cross sections. However, now that relativistic heavy ion beams are available at the LBL Bevalac, some of the cross sections of interest can be measured at energies close to those of the cosmic ray nuclei being observed.

Kertzman, M. P.↗
NASA NTRS1985

Interactions of heavy nuclei, Kr, Xe and Ho, in light targets

Over the past few years, the HEAO-3 measurements of the abundances of ultra-heavy cosmic ray nuclei (Z 26) at earth have been analyzed. In order to interpret these abundances in terms of a source composition, allowance must be made for the propagation of the nuclei in the interstellar medium. Vital to any calculation of the propagation is a knowlege of the total and partial interaction cross sections for these heavy nuclei on hydrogen. Until recently, data on such reactions have been scarce. However, now that relativistic heavy ion beams are available at the LBL Bevalac, some of the cross sections of interest can be measured at energies close to those of the cosmic ray nuclei being observed. During a recent calibration at the Bevalac of an array similar to the HEAO-C3 UH-nuclei detector, targets of raphite (C), polyethylene (CH2), and aluminum were exposed to five heavy ion beams ranging in charge (Z) from 36 to 92. Total and partial charge changing cross sections for the various beam nuclei on hydrogen can be determined from the measured cross sections on C and CH2, and will be applied to the propagation problem. The cross sections on Al can be used to correct the abundances of UH cosmic rays observed in the HEAO C-3 detector for interactions in the detector itself.

Kertzman, M. P.↗
NASA NTRS1989

Precision measurements of photoabsorption cross sections of Ar, Kr, Xe, and selected molecules at 58.4, 73.6, and 74.4 nm

Absolute absorption cross sections have been measured for the rare gases at 58.43, 73.59, and 74.37 nm with an accuracy of + or - 0.8 percent. For the molecules H2, N2, O2, CO, N2O, CO2, and CH4, precision measurements were made at 58.43 nm with an accuracy of + or - 0.8 percent. Molecular absorption cross sections are also reported at 73.59 and 74.37 nm. However, in the vicinity of these wavelengths most molecules exhibit considerable structure, and cross sections measured at these wavelengths may depend on the widths and the amounts of self-reversal of these resonance lines. A detailed discussion is given of the systematic errors encountered with the double-ion chamber used in the cross-sectional measurements. Details are also given of precision pressure measurements.

Samson, James A. R.↗
NASA NTRS1989

Interstellar SiC in the Murchison and Murray meteorites - Isotopic composition of Ne, Xe, Si, C, and N

Detailed ion-probe data are reported on Murchison and Murray C2 chondrites, along with noble-gas data on Murchison, with the purpose of characterizing the number and isotopic composition of independent SiC components and to link them to their stellar sources. Results show that coarse-grained and fine-grained SiC (totaling about 6-9 ppm of the two meteorites) contains record concentrations of two exotic components: Ne-E(H) (nearly monoisotopic Ne-22) and Se-S (enriched in isotopes 128, 130, and 132), respectively. The Ne-21 content was found to exceed up to 40-fold the content expected from the recent cosmic-ray irradiation, implying a presolar cosmic-ray exposure age of about 39 Ma. This age is much shorter that the predicted 500 Ma lifetime of refractory interstellar grains and implies either a selective interstellar destruction process for SiC, enhanced supernova activity in the protosolar neighborhood, or late outgassing of greater than 90 percent of the SiC.

Zinner, Ernst↗
NASA NTRS1999

An experimental study of the isotopic enrichment in Ar, Kr, and Xe when trapped in water ice

The isotopic enrichment of argon, krypton, and xenon, when trapped in water ice, was studied experimentally. The isotopes were found to be enriched according to their (m1/m2)1/2 ratio. These enrichment factors could be useful for comparison among the uncertain cosmic or solar isotopic ratios, the hopeful in situ cometary ratio, and those in Earth's atmosphere, in the context of cometary delivery of volatiles to Earth.

NASA Discipline Exobiology↗
NASA NTRS2004

The I-Xe Record of Long Equilibration in Chondrules from the Unnamed Antarctic Meteorite L3/LL3

The unnamed Antarctic meteorite studied here is of primitive chondritic type L3 or LL3, probably of grade 3.5 - 3.6. Detailed mineralogical and SEM analyses have revealed the existence of three distinct chondrule types in this meteorite. Both iron-rich and some iron-poor chondrules are present with variably recrystallized matrices or mesostases reflecting variable equilibration. Patchy equilibration of chondrule mesostases suggests thermal metamorphism after accretion. Additional information is included in the original extended abstract.

Pravdivtseva, O. V.↗
NASA NTRS2004

Compatibility of Niobium Alloys and Superalloys in a Flowing He-Xe Power Conversion System

Proposed concepts for an ambitious mission to explore Jupiter's three icy moons place significant demands on the various spacecraft systems. There are many challenges related to the high output power conversion systems being considered, and one example is the need to ensure system compatibility at all levels. The utilization of appropriate materials for component structures is important to ensuring long mission life. Refractory metal alloys have attractive high-temperature properties in inert environments, but these alloys are sometimes susceptible to contamination. Potential material compatibility issues exist between refractory metal candidates and more conventional alloys. Nb-1Zr has long been considered one of the most well characterized refractory alloys that is well suited for elevated-temperature use and liquid-metal compatibility. However, previous studies have suggested that niobium alloys can not co-exist in a closed system with traditional stainless steels or superalloys due to transport of contaminants. The relevance of this information to a proposed power conversion system is discussed. Also, experiments and fundamental calculations are being performed to determine contamination transport from candidate superalloys to Nb-1Zr in a closed system with an inert carrier gas. Potential protective schemes are explored to ensure system level compatibility between the refractory alloy Nb-1Zr and a nickel-based superalloy.

Bowman, Cheryl L.↗
NASA NTRS1996

Absolute Inelastic Differential Electron Scattering Cross Sections for He, Xe, N2, and CO at Near Threshold Impact Energies for 90(deg) Scattering Angle

There is a great deal of need for accurate differential cross sections (DCSs) associated with electron impact excitation of various atomic and molecular species. These cross sections are needed for modeling of various plasma systems (ranging from lasers and material processing plasmas to planetary and astrophysical plasmas) and for guiding development of theoretical and computational schemes.

DCS beam scattering beam-beam scattering↗