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The apparatus and experimental procedures used to obtain total electron scattering cross sections are described, and results are presented for He, Ne, Ar and Xe in the 4-300 eV incident energy range, together with statistical errors. The results are generally found to be in good agreement with previous data except at low impact energies. Serious discrepancies remain in Xe below 20 eV impact energy.
Results on the implantation of Kr and Xe in W under closed system conditions at very low energies (50-500 eV) are reported. Investigation of the fraction of gas trapped as a function of time reveals the existence of competing trapping and release mechanisms, and analysis of recovered trapped gas and residual gas phases shows that both elemental and isotropic fractionation result from these mechanisms. It is determined that the mass dependence for the overall implantation process is at or near m exp 1, with heavier isotopes enriched in the implanted gas. This mass dependence is inferred to result from implantation and a combination of diffusive and gas sputtering release mechanisms. These results reaffirm the conclusion of Bernatowicz and Fahey (1986) that previously observed isotopic fractionation of Kr and Xe in carbonaceous material synthesized in electrical discharges owes its origin to low-energy ion implantation, and also suggest that this process may be relevant to incorporation of noble gases in early solar system materials. The implication of these results for noble gas mass spectrometry are discussed.
The carriers of presolar noble gases were studied by isotopically analyzing 19 separates from the Murray and Murchison C2 chondrites for Ne, Xe, C, and N. It is found that the carriers of Ne-E(H) and Xe-S are resistant to HCl, HF, boiling HClO4, and CrO3-H2SO4, and thus must be either diamond or some resistant carbide or oxide. The carrier of Ne-E(L) may be some form of amorphous carbon with delta C13 of about +340 percent. A new carbon component, C theta, found as 0.2-2-micron inclusions in Murchison spinel, is amorphous and contains little or no noble gas. A new heavy nitrogen component is found which has an abundance of about 1 ppm in the bulk meteorite, combusts at 450-500 C, and may be associated wtih isotopically normal carbon or with C-alpha.
Simple Si2O3 smokes have been condensed at both low (less than 750 K) and high (greater than 1000 K) temperature at 35 torr H2 pressure in the presence of 0, 10, 100, and 1000 microns of a noble gas mixture containing Ne, Ar, Kr, and Xe. In general, both Ne and Ar are quite loosely bound in the smokes (6.0 x 10 to the -8th and 2.6 x 10 to the -4th ccSTP/g, respectively), and are degassed at temperatures below 1200 K. Both Kr and Xe are somewhat more strongly bound at concentrations of 1.0 x 10 to the -7th and 8.2 x 10 to the -8th ccSTP/g, respectively, and in addition show a double release with a second component at a temperature of about 1875 K. With the exception that Si2O3 smokes appear to show a particular affinity for argon, possibly due to an anomalous absorption of atmospheric argon, none of the other noble gases are found in sufficient concentration to explain the gases observed in meteorites as primary circumstellar condensates. However, this data in conjunction with observations of Honda et al. (1979) do seem to show a degree of dependence between noble gas retention and chemical composition.
In the past 14 years, I-Xe studies have been performed on nearly 100 individual chondrules from five different meteorites. More than half the studied chondrules come from the unequilibrated ordinary chondrites (UOC's) Chainpur, Semarkona, and Tieschitz. However, 'unequilibrated' does not necessarily mean 'unaltered,' and the I-Xe studies of chondrules from UOC's have ultimately been interpreted in terms of postformation alteration. Two types of constraints on chondrule formation are discussed: (1) the duration, location, and timing of postformation alteration (in solids over a 50-m.y. span); and (2) the ages of the earliest formed chondrules (a few million years after the earliest solids).
We present a model of the steady-state transport assuming three reservoirs: a lower mantle (P) with a relatively undepleted inventory of U, Th, Pu, I, He, Ne, Xe, Ar; an upper mantle that has been extensively outgassed (D); and the atmosphere. There is mass transport at a rate M(sub PD) by plumes from the lower mantle, a fraction of which is outgassed directly into the atmosphere, while the remainder feeds matter and associated nuclei into D. D is well outgassed at spreading centers and has material containing atmospheric gases added to it by subduction. In the case of He, there is no subduction component. The approach follows the treatment of Kellogg and Wasserburg. A summary of the pertinent equations and constraints was reported earlier. The U, Th and Pu in P are estimated for Earth models from refractory element abundances in meteorites. In this model the inventory of rare gases in D is governed by the simple mixing of components from P (both radiogenic and original) with distinctive atmospheric components. In addition, alpha decay and spontaneous fission of U, and (alpha, n) reaction on oxygen from energetic alpha particles produce radiogenic/nuclear daughter products in D. These include (4)He, (136)Xe and (21)Ne. (40)K in D generates excess radiogenic (40)Ar.
Individual mineral grains from a silicate inclusion of the Colomera IIE iron meteorite were studied by laser extraction to find suitable host phases for I-Xe dating. K-feldspar separate yields an I-Xe age of 4.552 Ga and a cooling rate of 4-16 C/Ma.
Old I-Xe age for Orgueil (and Murchison) magnetite is not confirmed. New results show closure 2.8 Ma after Shallowater/Bjurbole standard, 10.3 Ma later than previously reported. The anomalously old I-Xe age of Allegan feldspar is attributed to shock.
NASA’s OSIRIS-REx mission delivered to Earth 121.6 g of regolith material from asteroid Bennu on 24th September 2023. We report multi-step laser pyrolysis xenon isotopic analysis to investigate the I-Xe system in individual particles separated from aggregate material (a mixture of small particles of undefined lithology). The high sensitivity of the RELAX mass spectrometer allows us to observe small excesses of individual isotopes and separate out different components, which may not be possible using a conventional noble gas mass spectrometer. The temperature resolution of RELAX is sufficient to seek an I-Xe isochron from step heating analysis of a sample mass <100 μg, which can contribute to our understanding of the nature and timing of aqueous alteration on Bennu’s parent body. We also aim to better estimate and understand the iodine concentration of CI chondrite-like material.
Performance testing of NERVA XE-1 control drum actuator to determine its ability to function in closed loop positioning system
Xe gas addition effects on operating efficiency of carbon dioxide-helium-nitrogen laser
Cesium beam velocity attenuation by He, Kr and Xe, determining scattering cross sections from gas pressure and density measurements
Absorptivity, transition probability and collision broadening frequency of dimethylether at 3.51 micron He-Xe laser wavelength, noting pressure dependence, transition lifetime and saturation intensity
Ne, Ar, Kr and Xe ionized states transition and level lifetimes from photographically recorded beam foil spectra, discussing particle energies
Isotopic abundances and concentrations of spallogenic Ne, Kr and Xe in Apollo 12 rock 12002, constructing three stage model of irradiation history
Electron impact energy-loss spectra of Xe have been studied at 20 eV incident electron energy at scattering angles from 5 to 135 deg. Differential and integral cross sections for elastic scattering and for the excitation of electronic states up to 10.60 eV energy loss have been determined. The validity of the optical selection rules and the previously established angular behavior associated with direct and exchange processes were examined for this intermediate coupling case.
Direct nuclear pumping of an (He-3)-Xe laser, lasing at 2.63 microns, has been achieved. Scaling of the laser output with xenon concentration, total pressure, and thermal neutron flux has been investigated. A peak power in excess of 200 W was obtained at a total pressure of 3 atm, a gas mixture consisting of 5% xenon and 95% He-3, and a peak thermal flux of 6 x 10 to the 16th n/sq cm s.
Initial iodine isotopic compositions have been obtained for 10 individual chondrules from the meteorite Bjurbole, with a total range in well determined values of 6.5%, which would correspond to an age difference of 1.6 m.y. These results can be interpreted as distinct formation ages, metamorphic ages, or isotopic inhomogeneities in the early solar system, and can serve to constrain models for chondrule formation. Two of the chondrules show evidence of either isotopic inhomogeneities or disturbances of their I-Xe systems.