Das Hantgemal des Codex Falkensteinensis und anderer Fundstellen

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He and Ne ages of large presolar silicon carbide grains: Solving the recoil problem

Knowledge about the age of presolar grains provides important insights into Galactic chemical evolution and the dynamics of grain formation and destruction processes in the Galaxy. Determination from the abundance of cosmic ray interaction products is straightforward, but in the past has suffered from uncertainties in correcting for recoil losses of spallation products. The problem is less serious in a class of large (tens of micrometer) grains. We describe the correction procedure and summarise results for He and Ne ages of presolar SiC "Jumbo" grains that range from close to zero to ~850 Myr, with the majority being less than 200 Myr. We also discuss the possibility of extending our approach to the majority of smaller SiC grains and explore possible contributions from trapping of cosmic rays.Comment: Publications of the Astronomical Society of Australia, Contribution to PASA special volume "The Origin of Elements Heavier than Iron in honor of the 70th birthday of Roberto Gallino

Az anyag attoszekundumos dinamikája ultraintenzív lézerterekben optikai cikluson belülii időbeli és hullámhosszon belüli, nanométeres térbeli tartományokban = Attosecond dynamics of matter in ultra-high laser fields with sub-cycle temporal and sub-wavelength, nanometer-scale spatial resolution

Bebizonyítottuk, hogy az elektronok intenzív kvantált sugárzási térrel való kölcsönhatása fotonszám-fázis minimális bizonytalanságú, különleges statisztikájú fotonállapotok kialakulását eredményezi. Elemeztük a foton-elektron összefonódást, a Hanbury Brown és Twiss (HBT) típusú korrelációk extrém (attoszekundumos) fényjelek diagnosztikájában való alkalmazhatóságát, és általunk bevezetett „attoszekundumos sörétzaj” szerepét. A felületeken (pl. vékony fémrétegen, plazmarétegen és grafénen) lejátszódó intenzív lézer-anyag kölcsönhatásoknál elemeztük az ún. vivő-burkoló fázis szerepét különböző nemlineáris folyamatokban. Kifejlesztettük az elektronok kétdimenziós kinematikájának Wigner-függvényes leírását. Az ultrarövid fényimpulzusok grafénen történő szóródásának elemzése során általunk előrejelzett „relativisztikus levágás” optikai négyszögimpulzusok generálását teheti lehetővé. Kísérletileg észleltük és elméletileg értelmeztük felületi plazmonok térerősítését, s az evaneszcens terek nemlineáris optikai hatásait (felharmonikus-keltés, sokfotonos elektron emisszió és gyorsítás), és demonstráltuk, hogy az elektronok 2-3 femtoszekundumos csomagokban hagyják el a fémfelületet, az intenzitás-bulkolót követve. A plasmon-bomláskor (kollektív fékezési sugárzásakor) keletkező ultrarövid fényjelek nemklasszikus HBT-korrelációját, és a fotoncsomósodásból a ritkulásba való átmenetet elsőként mutattuk ki és értelmeztük az általunk kidolgozott elmélet alapján. | We analysed entanglement in the interaction of electrons with a strong quantized radiation field, which leads to the generation of number-phase minimum uncertainty states. On the basis of these results we introduced the concept of ""attosecond shot-noise"" and shown how the Hanbury Brown and Twiss (HBT) type correlations can be used for probing extreme light signals. We developed the Wigner function description of the kinematics of electrons in two-dimensional geometry. We studied in details the role of carrier-envelope phase difference effects in strong field laser- matter interactions at surfaces (thin metal or plasma layers and graphene). We predicted the new phenomena of ""relativistic clipping"" appearing in the scattering of ultrasort pulses on graphene, which may lead to rectangular optical pulses. We have observed experimentally and described theoretically that in surface plasmon enhanced evanescent electric fields, strong-field optics effects exist (high-harmonic generation, nonlinear electron emission and acceleration). These are characteristic for surface plasmon physics, they otherwise occur only in fields, higher than those produced by our exciting laser. We demonstrated that the electrons leave the surface in 2-3 fs-long bunches, following the intensity envelope of the surface plasmons. We measured and theoretically interpreted for the first time HBT type correlations in decaying surface plasmon light, and found the transition from antibunching to bunching

Origin and age of submarine ferromanganese hardgrounds from the Marion Plateau, offshore northeast Australia

Be and Nd isotope compositions and metal concentrations (Mn, Fe, Co, Ni, and Cu) of surface and subsurface ferromanganese hardground crusts from Ocean Drilling Program Leg 194 Marion Plateau Sites 1194 and 1196 provide new insights into the crusts' genesis, growth rates, and ages. Metal compositions indicate that the hardgrounds, which have grown on erosional surfaces in water depths of <400 m because of strong bottom currents, are not pure hydrogenetic precipitates. Nevertheless, the ratios between cosmogenic 10Be and stable 9Be in hardgrounds from the present-day seafloor at Site 1196 between 1 x 10–7 and 1.5 x 10–7 are within the range of values expected for Pacific seawater, which shows that the hardgrounds recorded the isotope composition of ambient seawater. This is also confirmed by their Nd isotope composition (Nd between –3 and 0). The 10Be/9Be ratios in the up to 30-mm-thick and partly laminated hardgrounds do not show a decrease with depth, which suggests high growth rates on the present-day seafloor. The subsurface crust at Site 1194 (117 m below the seafloor) grew during a sedimentation hiatus, when bottom currents in the late Miocene prevented sediment accumulation on the carbonate platform during a sea level lowstand. The age of 8.65 ± 0.50 Ma for this crust obtained from 10Be-based dating agrees well with the combined seismostratigraphic and biostratigraphic evidence, which suggests an age for the hiatus between 7.7 and 11.8 Ma

He and Ne Ages of Large Presolar Silicon Carbide Grains: Solving the Recoil Problem

Knowledge about the age of presolar grains provides important insights into Galactic chemical evolution and the dynamics of grain formation and destruction processes in the Galaxy. Determination from the abundance of cosmic ray interaction products is straightforward, but in the past has suffered from uncertainties in correcting for recoil losses of spallation products. The problem is less serious in a class of large (tens of μm) grains. We describe the correction procedure and summarise results for He and Ne ages of presolar SiC ‘Jumbo' grains that range from close to zero to ∼850 Myr, with the majority being less than 200 Myr. We also discuss the possibility of extending our approach to the majority of smaller SiC grains and explore possible contributions from trapping of cosmic ray

Fragments of Late Eocene Earth-impacting asteroids linked to disturbance of asteroid belt

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Unusual sources of fossil micrometeorites deduced from relict chromite in the small size fraction in ~467 Ma old limestone

Extraterrestrial chrome spinel and chromite extracted from the sedimentary rock record are relicts from coarse micrometeorites and rarely meteorites. They are studied to reconstruct the paleoflux of meteorites to the Earth and the collisional history of the asteroid belt. Minor element concentrations of Ti and V, and oxygen isotopic compositions of these relict minerals were used to classify the meteorite type they stem from, and thus to determine the relative meteorite group abundances through time. While coarse sediment-dispersed extraterrestrial chrome-spinel (SEC) grains from ordinary chondrites dominate through the studied time windows in the Phanerozoic, there are exceptions: We have shown that ~467 Ma ago, 1 Ma before the breakup of the L chondrite parent body (LCPB), more than half of the largest (>63 μm diameter) grains were achondritic and originated from differentiated asteroids in contrast to ordinary chondrites which dominated the meteorite flux throughout most of the past 500 Ma. Here, we present a new data set of oxygen isotopic compositions and elemental compositions of 136 grains of a smaller size fraction (32–63 μm) in ~467 Ma old pre-LCPB limestone from the Lynna River section in western Russia, that was previously studied by elemental analysis. Our study constitutes the most comprehensive oxygen isotopic data set of sediment-dispersed extraterrestrial chrome spinel to date. We also introduce a Raman spectroscopy-based method to identify SEC grains and distinguish them from terrestrial chrome spinel with ~97% reliability. We calibrated the Raman method with the established approach using titanium and vanadium concentrations and oxygen isotopic compositions. We find that ordinary chondrites are approximately three times more abundant in the 32–63 μm fraction than achondrites. While abundances of achondrites compared to ordinary chondrites are lower in the 32–63 μm size fraction than in the >63 μm one, achondrites are approximately three times more abundant in the 32–62 μm fraction than they are in the present flux. We find that the sources of SEC grains vary for different grain sizes, mainly as a result of parent body thermal metamorphism. We conclude that the meteorite flux composition ~467 Ma ago ~1 Ma before the breakup of the LCPB was fundamentally different from today and from other time windows studied in the Phanerozoic, but that in contrast to the large size fraction ordinary chondrites dominated the flux in the small size fraction. The high abundance of ordinary chondrites in the studied samples is consistent with the findings based on coarse extraterrestrial chrome-spinel from other time windows

Determining the impactor of the Ordovician Lockne crater : oxygen and neon isotopes in chromite versus sedimentary PGE signatures

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 306 (2011): 149-155, doi:10.1016/j.epsl.2011.04.028.Abundant chromite grains with L-chondritic composition in the resurge deposits of the Lockne impact crater (458 Myr old; dia. ~10 km) in Sweden have been inferred to represent relict fragments of an impactor from the break-up of the L-chondrite parent body at 470 Ma. This view has been challenged based on Ir/Cr and platinum group element (PGE) patterns of the same resurge deposits, and a reinterpretation of the origin of the chromite grains. An impactor of the non-magmatic iron meteorite type was proposed instead. Here we show that single-grain oxygen and noble-gas isotope analyses of the chromite grains from the resurge deposits further support an origin from an L-chondritic asteroid. We also present PGE analyses and Ir/Cr ratios for fossil L-chondritic meteorites found in mid-Ordovician marine limestone in Sweden. The L-chondritic origin has been confirmed by several independent methods, including major element and oxygen isotopic analyses of chromite. Although the meteorites show the same order-of-magnitude PGE and Cr concentrations as recent L chondrites, the elements have been redistributed to the extent that it is problematic to establish the original meteorite type from these proxies. Different PGE data processing approaches can lead to highly variable results, as also shown here for the Lockne resurge deposits. We conclude that the Lockne crater was formed by an L-chondritic impactor, and that considerable care must be taken when inferring projectile type from PGEs in sedimentary ejecta deposits.The WiscSIMS Lab is partially funded by NSF-EAR (0319230, 0516725, 0744079). The Robert A. Pritzker Center for Meteoritics and Polar Studies is supported by the Tawani Foundation

Heavy Element Abundances in Presolar Silicon Carbide Grains from Low-Metallicity AGB Stars

Primitive meteorites contain small amounts of presolar minerals that formed in the winds of evolved stars or in the ejecta of stellar explosions. Silicon carbide is the best studied presolar mineral. Based on its isotopic compositions it was divided into distinct populations that have different origins: Most abundant are the mainstream grains which are believed to come from 1.5-3 Msun AGB stars of roughly solar metallicitiy. The rare Y and Z grains are likely to come from 1.5-3 Msun AGB stars as well, but with subsolar metallicities (0.3-0.5x solar). Here we report on C and Si isotope and trace element (Zr, Ba) studies of individual, submicrometer-sized SiC grains. The most striking results are: (1) Zr and Ba concentrations are higher in Y and Z grains than in mainstream grains, with enrichments relative to Si and solar of up to 70x (Zr) and 170x (Ba), respectively. (2) For the Y and Z grains there is a positive correlation between Ba concentrations and amount of s-process Si. This correlation is well explained by predictions for 2-3 Msun AGB stars with metallicities of 0.3-0.5x solar. This confirms low-metallicity stars as most likely stellar sources for the Y and Z grains