Stable isotopes in diatom silica

Diatom silica is a form of biogenic opal (SiO2.nH2O, Figure 1) containing oxygen, silicon, carbon and nitrogen isotopes that can be used in lacustrine and marine paleoenvironmental studies. Since diatoms bloom following a seasonal pattern defined partly by the variability of climate, nutrient supply, mixing regimes, and in high latitudes the period of ice cover, the isotope signature acquired by diatoms will be skewed toward their major growing season specific to the lake or oceanic region under consideration. The isotope ratio (e.g. 18O/16O, 30Si/28Si, 13C/12C, 15N/14N) of diatom silica are expressed on the deltascale (δ) in terms of per mille (or per mille) (‰): δ = [(Rsample/Rreference) – 1] • 1000 ‰ Where R is the particular isotope ratio (e.g. 18O/16O, 30Si/28Si), and ‘reference’ means the appropriate universally accepted reference material. The ‘δ’ for each element takes its name from the heavy isotope, thus δ18O, δ30Si, δ13C, δ15N. For diatom oxygen the reference is VSMOW (Vienna Standard Mean Ocean Water) calibrated through the quartz NBS28, for silicon it is referenced and measured alongside NBS28, for carbon the reference is VPDB (Vienna PeeDee Belemnite) calibrated against NBS19 and NBS22, and for nitrogen it is atmospheric nitrogen, commonly shortened to AIR. There are no universally accepted standard materials to analyse alongside diatoms although most laboratories use their own standard diatomites as well as NBS quartz and low %C and %N organic materials

An integrated mineralogical, petrographic, light stable isotope and noble gas investigation of Sahara 99201 ureilite

New ureilite Sahara 99201 has been investigated to determine mineralogy, petrography, light stable isotopes and noble gases. The sample is a typical olivine pigeonite ureilite (Fo 78, Wo 10, En 72). C, N, O and Ar are consistent with other ureilites

Substitution of stable isotopes in Chlorella

Replacement of biologically important isotopes in the alga Chlorella by corresponding heavier stable isotopes produces increasingly greater deviations from the normal cell size and changes the quality and distribution of certain cellular components. The usefulness of isotopically altered organisms increases interest in the study of such permuted organisms

Gamow-Teller strength distributions in Fe and Ni stable isotopes

We study Gamow-Teller strength distributions in some selected nuclei of particular Astrophysical interest within the iron mass region. The theoretical framework is based on a proton-neutron Quasiparticle Random Phase Approximation built on a deformed selfconsistent mean field basis obtained from two-body density-dependent Skyrme forces. We compare our results to available experimental information obtained from (n,p) and (p,n) charge exchange reactions.Comment: 11 pages, 3 figure

First ice core records of NO3− stable isotopes from Lomonosovfonna, Svalbard

Samples from two ice cores drilled at Lomonosovfonna, Svalbard, covering the period 1957–2009, and 1650–1995, respectively, were analyzed for NO3− concentrations, and NO3− stable isotopes (δ15N and δ18O). Post-1950 δ15N has an average of (−6.9 ± 1.9) ‰, which is lower than the isotopic signal known for Summit, Greenland, but agrees with values observed in recent Svalbard snow and aerosol. Pre-1900 δ15N has an average of (4.2 ± 1.6) ‰ suggesting that natural sources, enriched in the 15 N-isotope, dominated before industrialization. The post-1950 δ18O average of (75.1 ± 4.1) ‰ agrees with data from low and polar latitudes, suggesting similar atmospheric NOy (NOy = NO + NO2 + HNO3) processing pathways. The combination of anthropogenic source δ15N and transport isotope effect was estimated as −29.1 ‰ for the last 60 years. This value is below the usual range of NOx (NOx = NO + NO2) anthropogenic sources which is likely the result of a transport isotope effect of –32 ‰. We suggest that the δ15N recorded at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions and forest fires; the first and second being responsible for the marked decrease in δ15N observed in the post-1950s record with soil emissions being associated to the decreasing trend in δ15N observed up to present time, and the third being responsible for the sharp increase of δ15N around 2000

Stable isotopes of Hawaiian spiders reflect substrate properties along a chronosequence.

The Hawaiian Islands offer a unique opportunity to test how changes in the properties of an isolated ecosystem are propagated through the organisms that occur within that ecosystem. The age-structured arrangement of volcanic-derived substrates follows a regular progression over space and, by inference, time. We test how well documented successional changes in soil chemistry and associated vegetation are reflected in organisms at higher trophic levels-specifically, predatory arthropods (spiders)-across a range of functional groups. We focus on three separate spider lineages: one that builds capture webs, one that hunts actively, and one that specializes on eating other spiders. We analyze spiders from three sites across the Hawaiian chronosequence with substrate ages ranging from 200 to 20,000 years. To measure the extent to which chemical signatures of terrestrial substrates are propagated through higher trophic levels, we use standard stable isotope analyses of nitrogen and carbon, with plant leaves included as a baseline. The target taxa show the expected shift in isotope ratios of δ15N with trophic level, from plants to cursorial spiders to web-builders to spider eaters. Remarkably, organisms at all trophic levels also precisely reflect the successional changes in the soil stoichiometry of the island chronosequence, demonstrating how the biogeochemistry of the entire food web is determined by ecosystem succession of the substrates on which the organisms have evolved

Hyperfine Quenching of the 4s4p3P04s4p ^{3}P_{0} Level in Zn-like Ions

In this paper, we used the multiconfiguration Dirac-Fock method to compute with high precision the influence of the hyperfine interaction on the $[Ar]3d^{10} 4s4p ^3P_0$ level lifetime in Zn-like ions for stable and some quasi-stable isotopes of nonzero nuclear spin between Z=30 and Z=92. The influence of this interaction on the $[Ar]3d^{10} 4s4p ^3P_1 - [Ar]3d^{10} 4s4p ^3P_0$ separation energy is also calculated for the same ions

Asymmetry Effects on Nuclear Fragmentation

We show the possibility of extracting important information on the symmetry term of the Equation of State ($EOS$) directly from multifragmentation reactions using stable isotopes with different charge asymmetries. We study n-rich and n-poor $Sn + Sn$ collisions at $50AMeV$ using a new stochastic transport approach with all isospin effects suitably accounted for. For central collisions a chemical component in the spinodal instabilities is clearly seen. This effect is reduced in the neck fragmentation observed for semiperipheral collisions, pointing to a different nature of the instability. In spite of the low asymmetry tested with stable isotopes the results are showing an interesting and promising dependence on the stiffness of the symmetry term, with an indication towards an increase of the repulsion above normal density.Comment: 8 pages (Latex), 7 Postscript figures, CRIS2000 Conference, Acicastello, Italy, May 22-26, (2000), Nucl. Phys. A (in press