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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Stopping relativistic Xe, Ho, Au and U nuclei in nuclear emulsions

Nuclei of Xe-54, Ho-67, Au-79 and U-92 accelerated at the Bevalac to energies between 1200 and 900 MeV/n were stopped in nuclear emulsions. The observed residual ranges were compared with those calculated from various models of energy loss and shown to be most consistent with a calculation that includes those higher order correction terms proposed previously to describe the energy loss of highly charged particles, for which the first Born approximation is not valid.

Waddington, C. J.↗
NASA NTRS1985

Stopping relativistic Xe, Ho, Au, and U nuclei in nuclear emulsions

Nuclei of Xe-54, Ho-67, Au-79 and U-92 accelerated at the Bevalac to energies between 1200 and 900 MeV/n were stopped in nuclear emulsions. The observed residual ranges were compared with those calculated from various models of energy loss and shown to be most consistent with a calculation that includes those higher order correction terms proposed previously to describe the energy loss of highly changed particles, for which the first Born approximation is not valid.

Waddington, C. J.↗
NASA NTRS1986

Adsorption and isotopic fractionation of Xe

A theoretical description of the mechanisms of isotopic fractionation arising during adsorption of noble gases in a Henry's Law pressure regime is given. Experimental data on the isotopic composition of Xe adsorbed on activated charcoal in the temperature range 220 K to 350 K are presented. Both theoretical considerations and the experimental data indicate that equilibrium adsorption does not significantly alter the isotopic structure of adsorbed structure of adsorbed noble gases. Therefore, if adsorption is responsible for the elemental noble gas pattern in meteorites and the earth, the heavy noble gas isotopic fractionation between them must have been produced prior to and by a different process than equilibrium adsorption.

Bernatowicz, T. J.↗
NASA NTRS1987

Half-collision analysis of far-wing diffuse structure in Cs-Xe

Laser excitation in the far red wing of the second principal series doublet of Cs mixed with Xe revealed a diffuse structure associated with the 2P(3/2) component. The structure is thought to originate from a reflection type of spectrum between the weakly bound E 2Sigma(1/2) excited state and the X 2Sigma(1/2) repulsive ground state of CsXe.

Exton, R. J.↗
NASA NTRS1985

Time-resolved laser-induced fluorescence of selected even-parity 7p states of Xe I

Lifetimes and self-quenching rates have been measured for excited states of Xe I that were populated using simultaneous two-photon absorption. Lifetimes measured in this study are somewhat shorter than those measured using the broadband-excitation technique. Lifetimes reported here are all faster than 100 nsec. Deactivation rates are approximately 2 x 10 to the -10th cu cm/sec per mol.

Mcgee, T. J.↗
NASA NTRS1991

Implanted He-3, He-4, and Xe in further studies of diamonds from Western Australia

In measurements of the noble gases in additional samples of diamonds from the Argyle and Ellendale lamproites in Western Australia, no neon-rich stones were encountered. No neon was detected above the relatively high blank levels in the glass apparatus. White and brown diamonds showed no differences in noble gas content, nor did samples segregated by the color of long-wave UF fluorescence. The rare gas patterns in the 1.2 Ga Argyle pipe are largely consistent with implanted He-3, He-4, and fissiogenic Xe from U/Th in the matrix rock in which the diamonds have been stored for so long. These implanted species are absent in diamonds from the much younger (about 20 Ma) Ellendale pipe. Implantation formulas for several models of inhomogeneously distributed U/Th are given. Differences in He-3 content between pipe and alluvial Argyle samples are consistent with expected cosmogenic production in the latter. An expanded data base for helium and carbon isotopic data on the same samples supports a negative (He-4)-delta(C-13) correlation seen in earlier work.

Mcconville, P.↗
NASA NTRS1992

Solubility and partitioning of Ne, Ar, Kr, and Xe in minerals and synthetic basaltic melts

The solubilities of Ne, Ar, Kr, and Xe gases were measured in natural samples of anorthite, diopside, forsterite, spinel, and synthetic basaltic melts, the samples which represent equilibrium pairs in the Fo-An-Di-SiO2 system. Results show that, in natural minerals, the solubilities of these gases increase with increasing atomic number. In contrast, the solubilities of noble gases in the synthetic basaltic melts decreased with increasing atomic number. The partition coefficients increased with increasing atomic number for all mineral/melt pairs.

Broadhurst, C. L.↗
NASA NTRS1991

Implanted 3He, 4He, and Xe in further studies of diamonds from Western Australia

In measurements of the noble gases in additional samples of diamonds from the Argyle and Ellendale lamproites in Western Australia we have failed to encounter any neon-rich stones such as showed solar-like isotopic compositions in earlier work. No neon was detected above the relatively high blank levels in our glass apparatus. White and brown diamonds showed no differences in noble gas content, nor did samples segregated by the color of long-wave UF fluorescence. The rare gas patterns in the 1.2 Ga Argyle pipe are largely consistent with implanted 3He, 4He, and fissiogenic Xe from U/Th in the matrix rock in which the diamonds have been stored for so long. These implanted species are absent in diamonds from the much younger (approximately 20 Ma) Ellendale pipe. We give implantation formulae for several models of inhomogeneously distributed U/Th. Differences in 3He content between pipe and alluvial Argyle samples are consistent with expected cosmogenic production in the latter. An expanded data base for helium and carbon isotopic data on the same samples supports a negative [4He]-delta 13C correlation seen earlier in work from our group, but if the Argyle samples, which contain light carbon, are corrected for implanted 4He, the correlation is considerably weakened. We no longer see an earlier 3He/4He-delta 13C correlation.

NASA Discipline Number 52-10↗
NASA NTRS2005

Ar-Ar and I-Xe Ages of Caddo County and Thermal History of IAB Iron Meteorites

Inclusions in IAB iron meteorites include non-chondritic silicate and those with more primitive chondritic silicate composition. Coarse-grained gabbroic material rich in plagioclase and diopside occurs in the Caddo County IAB iron meteorite and represents a new type of chemically differentiated, extra-terrestrial, andesitic silicate. Other parts of Caddo contain mostly andesitic material. Caddo thus exhibits petrologic characteristics of parent body metamorphism of a chondrite-like parent and inhomogeneous segregation of melts. Proposed IAB formation models include parent body partial melting and fractional crystallization or incomplete differentiation due to internal heat sources, and impact/induced melting and mixing. Benedix et al. prefer a hybrid model whereby the IAB parent body largely melted, then underwent collisional breakup, partial mixing of phases, and reassembly. Most reported 129I- Xe-129 ages of IABs are greater than 4.56 Gyr and a few are greater than or = 4.567 Gyr. These oldest ages exceed the 4.567 Gyr Pb-Pb age of Ca, Al-rich inclusions in primitive meteorites,

Bogard, Donald D.↗
NASA NTRS2005

Rare Gases Inserted into Biological Building Blocks: A Theoretical Study of Glycine - Rg Compounds (Rg-Xe, Kr, Ar)

Compounds formed by insertion of rare-gas atoms (Xe, Kr, and Ar) into glycine molecule are investigated using accurate ab initio computational methods. Identification of such insertion compounds may open new frontiers in the field of rare-gas chemistry, such as possible existence of biological molecules that include chemically bound rare gas atoms. The most stable glycine-Rg configuration is found to correspond to insertion of Rg atoms into the 0-H bond of glycine. These NH2CH2COORgH compounds are metastable , but separated by sizable potential barriers from the Rg + glycine dissociation products. Preliminary calculations show that NH2CH2COOXeH compound is energetically stable with respect to another (3-body) dissociation channel (NH2CH2COO + Rg + H), while the corresponding Ar species is not stable in this respect. The compound with the inserted Kr is a borderline case, with the 3-body dissociation products being close in energy to the NH2CH2COOKrH minimum.

Chaban, Galina M.↗
NASA NTRS1996

Electron Impact Excitation of Autoionizing Levels of Kr and Xe Between the (sup 2)P(sub 3/2) and (sup 2)P(sub 1/2) Ionic Limits

We have observed electrons ejected from autoionizing levels which lie between the (sup 2)P(sub 3/2) and (sup 2)P(sub 1/2) ionic limits for Kr and Xe. Kinetic energy spectra of the ejected electrons were obtained following electron impact excitation of the target gases by using time-of-flight spectroscopy in a crossed beam experiment. Spectral features which correspond to electrons ejected from both odd and even parity autoionizing levels have been identified.

autoionizing ejected electrons↗