Browsing by Author "Lynn, GW"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    New approach to quantification of metamorphism using ultra-small and small angle neutron scattering
    (Elsevier, 2009-12-15) Anovitz, LM; Lynn, GW; Cole, DR; Rother, G; Allard, LF; Hamilton, WA; Porcar, L; Kim, MH
    In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to similar to 1700 m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering Curve with a slope less than -4 appears Lit low-Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore Volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock in a manner that is difficult to achieve using high-resolution imaging (e.g. TEM). Thus, neutron scattering techniques provide a new approach to the analysis and study of metamorphism. © 2009, Elsevier Ltd.
  • No Thumbnail Available
    Item
    New approach to quantification of metamorphism using ultra-small and small angle neutron scattering
    (Elsevier; Cambridge Publications, 2008-07) Anovitz, LM; Lynn, GW; Cole, DR; Rother, G; Allard, LF; Hamilton, WA; Porcar, L; Kim, MH
    Small- and Ultra-Small Angle Neutron Scattering (SANS and USANS) provide powerful tools for analysis of porous rocks because neutrons probe both the surface and the interior of the material providing bulk statistical information over a wide range of length scales. For monomineralic materials scattering contrast arises from the difference between the scattering length density of the rock and the pores (taken to be zero). Pore-grain interfaces are best described by self-similar fractals with non-universal dimensions (2 < D < 3). This leads to a non-integer power-law as a function of the scattering I(Q) = I(1)Q-a + B where B is the incoherent background. For a volume or mass fractal scatterer a = D; if only the surface is a fractal, then a = 6-D. In this manner, surface fractals (a>3) and mass fractals (a<3) are easily distinguished. Non-fractal “fuzzy” interfaces (a>4) may also be observed. We have used SANS and USANS to characterize samples from two transects (contact out to ~1700 m) from the contact metamorphosed Hueco limestone at Marble Canyon, TX. Significant changes in a number of scattering parameters are observed as a function of distance, including regions of the aureole outside the range of classic reaction petrology. Our modeling suggests that changes in surface free energy, pore volume and hydrogen content, among other variables, can be quantified. Both the mass and surface fractals Dm and Ds can be fitted as a function of the surface fractal correlation length as: log10(D/r) = -0.9648 * log10r(Å) + 0.30103 r2 = 0.9999, s = 0.038 although metamorphism does not necessarily proceed linearly along this curve with increasing grade. Nonetheless, the ability to measure these variables shows that these techniques provide a novel approach to the analysis and study of metamorphism.
  • No Thumbnail Available
    Item
    New sources and instrumentation for neutrons in biology
    (Elsevier, 2008-04-18) Teixeira, SCM; Zaccai, G; Ankner, J; Bellissent-Funel, MC; Bewley, RI; Blakeley, MP; Callow, P; Coates, L; Dahint, R; Dalgliesh, R; Dencher, NA; Forsyth, VT; Fragneto, G; Frick, B; Gilles, R; Gutberlet, T; Haertlein, M; Hauß, T; Häußler, W; Heller, WT; Herwig, K; Holderer, O; Juranyi, F; Kampmann, R; Knott, RB; Krueger, S; Langan, P; Lechner, RE; Lynn, GW; Majkrzak, CF; May, RP; Meilleur, F; Mo, Y; Mortensen, K; Myles, DAA; Natali, F; Neylon, C; Niimura, N; Ollivier, J; Ostermann, A; Peters, J; Pieper, J; Rühm, A; Schwahn, D; Shibata, K; Soper, AK; Strässle, T; Suzuki, J; Tanaka, I; Tehei, M; Timmins, P; Torikai, N; Unruh, T; Urban, V; Vavrin, R; Weiss, K
    Neutron radiation offers significant advantages for the study of biological molecular structure and dynamics. A broad and significant effort towards instrumental and methodological development to facilitate biology experiments at neutron sources worldwide is reviewed. © 2008, Elsevier Ltd.