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Title: Ultra-small-angle neutron scattering with azimuthal asymmetry

Abstract

Small-angle neutron scattering (SANS) measurements from thin sections of rock samples such as shales demand as great a scattering vector range as possible because the pores cover a wide range of sizes. The limitation of the scattering vector range for pinhole SANS requires slit-smeared ultra-SANS (USANS) measurements that need to be converted to pinhole geometry. The desmearing algorithm is only successful for azimuthally symmetric data. Scattering from samples cut parallel to the plane of bedding is symmetric, exhibiting circular contours on a two-dimensional detector. Samples cut perpendicular to the bedding show elliptically dependent contours with the long axis corresponding to the normal to the bedding plane. A method is given for converting such asymmetric data collected on a double-crystal diffractometer for concatenation with the usual pinhole-geometry SANS data. Furthermore, the aspect ratio from the SANS data is used to modify the slit-smeared USANS data to produce quasi-symmetric contours. Rotation of the sample about the incident beam may result in symmetric data but cannot extract the same information as obtained from pinhole geometry.

Authors:
 [1];  [2]
  1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Geosciences
  2. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). NIST Center for Neutron Research
Publication Date:
Research Org.:
Pennsylvania State Univ., University Park, PA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1345573
Grant/Contract Number:
FG02-05ER15675
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Applied Crystallography (Online)
Additional Journal Information:
Journal Name: Journal of Applied Crystallography (Online); Journal Volume: 49; Journal Issue: 3; Journal ID: ISSN 1600-5767
Publisher:
International Union of Crystallography
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 97 MATHEMATICS AND COMPUTING; azimuthal asymmetric scattering; double-crystal diffractometers; elliptic scattering contours; slit-height smeared scattering; small-angle neutron scattering

Citation Formats

Gu, X., and Mildner, D. F. R. Ultra-small-angle neutron scattering with azimuthal asymmetry. United States: N. p., 2016. Web. doi:10.1107/s1600576716005586.
Gu, X., & Mildner, D. F. R. Ultra-small-angle neutron scattering with azimuthal asymmetry. United States. doi:10.1107/s1600576716005586.
Gu, X., and Mildner, D. F. R. Mon . "Ultra-small-angle neutron scattering with azimuthal asymmetry". United States. doi:10.1107/s1600576716005586. https://www.osti.gov/servlets/purl/1345573.
@article{osti_1345573,
title = {Ultra-small-angle neutron scattering with azimuthal asymmetry},
author = {Gu, X. and Mildner, D. F. R.},
abstractNote = {Small-angle neutron scattering (SANS) measurements from thin sections of rock samples such as shales demand as great a scattering vector range as possible because the pores cover a wide range of sizes. The limitation of the scattering vector range for pinhole SANS requires slit-smeared ultra-SANS (USANS) measurements that need to be converted to pinhole geometry. The desmearing algorithm is only successful for azimuthally symmetric data. Scattering from samples cut parallel to the plane of bedding is symmetric, exhibiting circular contours on a two-dimensional detector. Samples cut perpendicular to the bedding show elliptically dependent contours with the long axis corresponding to the normal to the bedding plane. A method is given for converting such asymmetric data collected on a double-crystal diffractometer for concatenation with the usual pinhole-geometry SANS data. Furthermore, the aspect ratio from the SANS data is used to modify the slit-smeared USANS data to produce quasi-symmetric contours. Rotation of the sample about the incident beam may result in symmetric data but cannot extract the same information as obtained from pinhole geometry.},
doi = {10.1107/s1600576716005586},
journal = {Journal of Applied Crystallography (Online)},
number = 3,
volume = 49,
place = {United States},
year = {Mon May 16 00:00:00 EDT 2016},
month = {Mon May 16 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 3works
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  • 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 {approx}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 asmore » 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 at 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.« less
  • No abstract prepared.
  • No abstract prepared.
  • We have used ultra-small-angle neutron scattering (USANS) with contrast variation to measure the porosity (voids and binder-filled regions) in a composite high explosive, PBX 9501, formulated with a deuterated binder. Little is known about the microstructure of pressed PBX 9501 parts and thus how it is affected by processing. Here, we explore the effect of varying the pressing intensity on the PBX 9501 microstructure. Disk-shaped samples of PBX 9501 were die-pressed with applied pressures ranging between 10,000 and 29,000 psi at 90 C. Five samples were prepared at each pressure that differed in the fraction of deuterated binder, facilitating variationmore » of the neutron scattering length density contrast ({Delta}{rho}) and thus, the resolution of microstructural details. The sample composition was determined by calculation of the Porod Invariant as a function of {Delta}{rho} and compared with compositional estimates obtained from the bulk sample density. Structural modeling of the USANS data, at different levels of contrast, assuming both spherical and cylindrical morphologies, allowed the mean size and size distribution of voids and binder-filled regions to be determined. A decrease in the mean diameter of binder-filled regions was found with increasing pressing intensity, while the mean void diameter showed no significant change.« less
  • Small- and Ultra-Small Angle Neutron Scattering (SANS and USANS) provide powerful tools for quantitative analysis of porous rocks, yielding bulk statistical information over a wide range of length scales. This study utilized (U)SANS to characterize shallowly buried quartz arenites from the St. Peter Sandstone. Backscattered electron imaging was also used to extend the data to larger scales. These samples contain significant volumes of large-scale porosity, modified by quartz overgrowths, and neutron scattering results show significant sub-micron porosity. While previous scattering data from sandstones suggest scattering is dominated by surface fractal behavior over many orders of magnitude, careful analysis of ourmore » data shows both fractal and pseudo-fractal behavior. The scattering curves are composed of subtle steps, modeled as polydispersed assemblages of pores with log-normal distributions. However, in some samples an additional surface-fractal overprint is present, while in others there is no such structure, and scattering can be explained by summation of non-fractal structures. Combined with our work on other rock-types, these data suggest that microporosity is more prevalent, and may play a much more important role than previously thought in fluid/rock interactions.« less