Heavy noble gases in solar wind delivered by Genesis mission

One of the major goals of the Genesis Mission was to refine our knowledge of the isotopic composition of the heavy noble gases in solar wind and, by inference, the Sun, which represents the initial composition of the solar system. This has now been achieved with permil precision: ^(36)Ar/^(38)Ar = 5.5005 ± 0.0040, ^(86)Kr/^(84)Kr = .3012 ± .0004, ^(83)Kr/^(84)Kr = .2034 ± .0002, ^(82)Kr/^(84)Kr = .2054 ± .0002, ^(80)Kr/^(84)Kr = .0412 ± .0002, ^(78)Kr/^(84)Kr = .00642 ± .00005, ^(136)Xe/^(132)Xe = .3001 ± .0006, ^(134)Xe/^(132)Xe = .3691 ± .0007, ^(131)Xe/^(132)Xe = .8256 ± .0012, ^(130)Xe/^(132)Xe = .1650 ± .0004, ^(129)Xe/^(132)Xe = 1.0405 ± .0010, ^(128)Xe/^(132)Xe = .0842 ± .0003, ^(126)Xe/^(132)Xe = .00416 ± .00009, and ^(124)Xe/^(132)Xe = .00491 ± .00007 (error-weighted averages of all published data). The Kr and Xe ratios measured in the Genesis solar wind collectors generally agree with the less precise values obtained from lunar soils and breccias, which have accumulated solar wind over hundreds of millions of years, suggesting little if any temporal variability of the isotopic composition of solar wind krypton and xenon. The higher precision for the initial composition of the heavy noble gases in the solar system allows (1) to confirm that, exept ^(136)Xe and ^(134)Xe, the mathematically derived U–Xe is equivalent to Solar Wind Xe and (2) to provide an opportunity for better understanding the relationship between the starting composition and Xe-Q (and Q-Kr), the dominant current “planetary” component, and its host, the mysterious phase-Q

Genesis Noble Gas Measurements

The original thrust of our Genesis funding was to extend and refine the noble gas analytical capabilities of this laboratory to improve the precision and accuracy of noble gas measurements in order to optimize the scientific return from the Genesis Mission. This process involved both instrumental improvement (supplemented by a SRLIDAP instrument grant) and refinement of technique. The Genesis landing mishap shifted our emphasis to the irregular aluminum heat shield material from the flat collector wafers. This has required redesign of our laser extraction cells to accommodate the longer focal lengths required for laser extraction from non-flat surfaces. Extraction of noble gases from solid aluminum surfaces, rather than thin coatings on transparent substrates has required refinement of controlled-depth laser ablation techniques. Both of these bring new problems, both with potentially higher blanks form larger laser cells and the larger quantities of evaporated aluminum which can coat the sapphire entrance ports. This is mainly a problem for the heavy noble gases where larger extraction areas are required, necessitating the new aluminum vapor containment techniques described below. With the Genesis Mission came three new multiple multiplier noble gas mass spectrometers to this laboratory, one built solely by us (Supergnome-M), one built in collaboration with Nu-Instruments (Noblesse), and one built in collaboration with GVI (Helix). All of these have multiple multiplier detection sections with the Nu-Instruments using a pair of electrostatic quad lenses for isotope spacing and the other two using mechanically adjustable positions for the electron multipliers. The Supergnome-M and Noblesse are installed and running. The GVI instrument was delivered a year late (in March 2005) and is yet to be installed by GVI. As with all new instruments there were some initial development issues, some of which are still outstanding. The most serious of these are performance issues with the miniature channel electron multipliers. The delayed installation of Helix by the GVI is partly due to failure of the initial batch of Burle channel multipliers to perform as expected. A number of the channel multipliers designed for Noblesse by Burle have also failed upon baking. Burle has now refined the design of these and we have installed two of the new multipliers and are assessing their performance. The remaining multipliers Will be upgraded to the new design from Burle once we confirm that the problem has been fixed

Fischer-Tropsch-Type Production of Organic Materials in the Solar Nebula: Studies Using Graphite Catalysts and Measuring the Trapping of Noble Gases

The formation of abundant carbonaceous material in meteorites is a long standing problem and an important factor in the debate on the potential for the origin of life in other stellar systems. The Fischer-Tropsch-type (FTT) catalytic reduction of CO by hydrogen was once the preferred model for production of organic materials in the primitive solar nebula. We have demonstrated that many grain surfaces can catalyze both FTT and HB-type reactions, including amorphous iron and magnesium silicates, pure silica smokes as well as several minerals. Graphite is not a particularly good FTT catalyst, especially compared to iron powder or to amorphous iron silicate. However, like other silicates that we have studied, it gets better with exposure to CO. N2 and H2 over time: e.g., after formation of a macromolecular carbonaceous layer on the surfaces of the underlying gains. While amorphous iron silicates required only 1 or 2 experimental runs to achieve steady state reaction rates, graphite only achieved steady state after 6 or more experiments. We will present results showing the catalytic action of graphite grains increasing with increasing number of experiments and will also discuss the nature of the final "graphite" grains aster completion of our experiments

Constraints on Neon and Argon Isotopic Fractionation in Solar Wind

To evaluate the isotopic composition of the solar nebula from which the planets formed, the relation between isotopes measured in the solar wind and on the Sun's surface needs to be known. The Genesis Discovery mission returned independent samples of three types of solar wind produced by different solar processes that provide a check on possible isotopic variations, or fractionation, between the solar-wind and solar-surface material. At a high level of precision, we observed no significant inter-regime differences in ^(20)Ne/^(22)Ne or ^(36)Ar/^(38)Ar values. For ^(20)Ne/^(22)Ne, the difference between low- and high-speed wind components is 0.24 ± 0.37%; for ^(36)Ar/^(38)Ar, it is 0.11 ± 0.26%. Our measured ^(36)Ar/^(38)Ar ratio in the solar wind of 5.501 ± 0.005 is 3.42 ± 0.09% higher than that of the terrestrial atmosphere, which may reflect atmospheric losses early in Earth's history

Measurement of one-particle correlations and momentum distributions for trapped 1D gases

van Hove's theory of scattering of probe particles by a macroscopic target is generalized so as to relate the differential cross section for atomic ejection via stimulated Raman transitions to one-particle momentum-time correlations and momentum distributions of 1D trapped gases. This method is well suited to probing the longitudinal momentum distributions of 1D gases in situ, and examples are given for bosonic and fermionic atoms.Comment: 4 pages, 2 .eps figure

Nonequilibrium Dynamics of Optical Lattice-Loaded BEC Atoms: Beyond HFB Approximation

In this work a two-particle irreducible (2PI) closed-time-path (CTP) effective action is used to describe the nonequilibrium dynamics of a Bose Einstein condensate (BEC) selectively loaded into every third site of a one-dimensional optical lattice. The motivation of this work is the recent experimental realization of this system at National Institute of Standards and Technology (NIST) where the placement of atoms in an optical lattice is controlled by using an intermediate superlattice. Under the 2PI CTP scheme with this initial configuration, three different approximations are considered: a) the Hartree-Fock-Bogoliubov (HFB) approximation, b) the next-to-leading order 1/$\mathcal{N}$ expansion of the 2PI effective action up to second order in the interaction strength and c) a second order perturbative expansion in the interaction strength. We present detailed comparisons between these approximations and determine their range of validity by contrasting them with the exact many body solution for a moderate number of atoms and wells. As a general feature we observe that because the second order 2PI approximations include multi-particle scattering in a systematic way, they are able to capture damping effects exhibited in the exact solution that a mean field collisionless approach fails to produce. While the second order approximations show a clear improvement over the HFB approximation our numerical result shows that they do not work so well at late times, when interaction effects are significant.Comment: 34 pages, 7 figure

White Matter Changes in Patients with Friedreich Ataxia after Treatment with Erythropoietin

Background and Purpose—Erythropoietin (EPO) has received growing attention because of its neuro-regenerative properties. Preclinical and clinical evidence supports its therapeutic potential in brain conditions like stroke, multiple sclerosis and schizophrenia. Also in Friedreich ataxia, clinical improvement after EPO therapy was shown. The aim of the present study was to assess possible therapy-associated brain white-matter changes in these patients.Methods—Nine patients with Friedreich ataxia underwent Diffusion Tensor Imaging (DTI) before and after EPO treatment. Tract-based spatial statistics (TBSS) was used for longitudinal comparison. Results—We detected widespread longitudinal increase in fractional anisotropy (FA) and axial diffusivity (D||) in cerebral hemispheres bilaterally (p<0.05, corrected), while no changes were observed within the cerebellum, medulla oblongata and pons. Conclusions—To the best of our knowledge, this is the first DTI study to investigate the effects of erythropoietin in a neurodegenerative disease. Anatomically, the diffusivity changes appear disease-unspecific, and their biological underpinnings deserve further study

Lunar and Planetary Surface Dynamics and Early History

The research described by this annual research report covers the following subjects: A) Early solar system processes and time scales using I-Xe chronometry; B) I-Xe studies of individual chondrules; C) Additional Ongoing Projects

Cosmogenic neon from individual grains of CM meteorites: extremely long pre-compaction exposure histories or an enhanced early particle flux

Meteoritic grains which contain solar flare VH ion tracks have clearly been individually exposed to energetic particles prior to assembly. In order to observe the effects of irradiation during the precompaction era, spallation-produced neon has been measured in individual grains, selected by the presence of solar flare VH tracks, from the CM regolith breccias Murchison, Murray, and Cold Bokkeveld. The presence of pre-compaction spallation neon correlates well with the presence of solar flare VH tracks (Z 20) and, in this study, detection of SF tracks is the critical parameter used to identify those grains where pre-compaction spallation effects are likely to be present. Only a few percent of the grains (at most) that do not contain solar flare VH tracks contain amounts of cosmogenic Ne larger than would be produced during the conventional cosmic-ray exposure age (and for them the excess is only marginal), whereas most of the grains with solar flare VH tracks contain spallation-produced Ne in significant excess of that due to the nominal cosmic-ray exposure. The magnitude of this excess, which clearly must have been produced prior to compaction, provides evidence for extensive energetic particle exposure during the pre-compaction era. If a contemporary energetic particle complex is assumed (galactic and solar cosmic rays: GCR and SCR), and if production is taken at the maximum present rates, minimum GCR pre-compaction exposure times can be found. The most heavily irradiated grains from Murray and Murchison would require a minimum GCR regolith exposure time of 145 Ma to accumulate the observed cosmogenic Ne. This is the lower limit because it is computed using the peak production rates from the GCR cascade, which occur at roughly 60 g/cm2 and it requires that the grain spent its entire regolith residence time at that optimum depth. Studies of compaction constraints for CI and CM meteorites suggest that such long regolith residence times may be unlikely. The alternative to such long periods of parent body regolith activity is increased production rates in the early solar system from an enhanced energetic particle environment