G.E Mitchell

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Publications (3)0 Total impact

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    Article: Isospin symmetry breaking and the nuclear shell model
    J.F Shriner, G.E Mitchell, B.A Brown
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    ABSTRACT: The effect of isospin symmetry breaking on level statistics has been examined with the nuclear shell model. The eigenvalues and electromagnetic transitions were calculated with the program OXBASH for the nuclide 26Al for conserved isospin and for broken isospin. The long-range correlations of the eigenvalues, as measured by Δ3, show good agreement between the experimental results and the calculations. However, there are discrepancies between data and calculations for the short-range correlations of the eigenvalues.
    Physics Letters B.
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    Article: Towards a detailed understanding of the NEXAFS spectra of bulk polyethylene copolymers and related alkanes
    A Schöll, R Fink, E Umbach, G.E Mitchell, S.G Urquhart, H Ade
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    ABSTRACT: High energy resolution C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of ethylene-1-alkene copolymers with systematic variations in comonomer content and thus systematic changes in branch length, branching ratio, and degree of crystallinity are presented. Spectral changes of the σ*C–H/Rydberg and σ*C–C features in these ideal model systems provide unambiguous experimental evidence for intermolecular interactions with profound effects on the spectral intensity, but only very small energy shifts. Ab initio calculations reproduce the experimental results in detail. The intermolecular interaction observed suggests that interpretation of NEXAFS spectra based on calculations of isolated molecules can be insufficient even in relatively weakly interacting macromolecules.
    Chemical Physics Letters.
  • Article: Optimization of scanning transmission X-ray microscopy for the identification and quantitation of reinforcing particles in polyurethanes
    A.P Hitchcock, I Koprinarov, T Tyliszczak, E.G Rightor, G.E Mitchell, M.T Dineen, F Hayes, W Lidy, R.D Priester, S.G Urquhart, A.P Smith, H Ade
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    ABSTRACT: The morphology, size distributions, spatial distributions, and quantitative chemical compositions of co-polymer polyol-reinforcing particles in a polyurethane have been investigated with scanning transmission X-ray microscopy (STXM). A detailed discussion of microscope operating procedures is presented and ways to avoid potential artifacts are discussed. Images at selected photon energies in the C 1s, N 1s and O 1s regions allow unambiguous identification of styrene–acrylonitrile-based (SAN) copolymer and polyisocyanate polyaddition product-based (PIPA) reinforcing particles down to particle sizes at the limit of the spatial resolution (50 nm). Quantitative analysis of the chemical composition of individual reinforcing particles is achieved by fitting C 1s spectra to linear combinations of reference spectra. Regression analyses of sequences of images recorded through the chemically sensitive ranges of the C 1s, N 1s and O 1s spectra are used to generate quantitative compositional maps, which provide a fast and effective means of investigating compositional distributions over a large number of reinforcing particles. The size distribution of all particles determined by STXM is shown to be similar to that determined by TEM. The size distributions of each type of reinforcing particle, which differ considerably, were obtained by analysis of STXM images at chemically selective energies.
    Ultramicroscopy.
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