Real-Time Observation of Slow Dynamics in Rocks Using Neutron Scattering
Abstract
Single-crystal quartz shows very little nonlinear behavior: porous aggregates of quartz (sandstones) can, however, display prodigious nonlinearities, of both classical (non-Hooke's Law, but reversible) and non-classical (irreversible, hysteretic) forms. The distribution of strain in the grains and grain-grain contacts is intimately connected to the bulk nonlinearity. The distribution resulting from applied uniaxial stress has been studied and can be found in the literature; however, the strains arising from temperature changes are different due to the overall expansion or contraction of the grains. Neutron scattering with its large probed volume is a way of determining the strain distribution and the time dependence associated with nonclassical behavior in a consolidated, polycrystalline, macroscopic rock. We have measured the macroscopic elastic, macroscopic thermal and atomic lattice response of several rocks, under "rapid" (i.e. ~30 min) temperature changes of around Δ T \approx 40K. Due to the high flux and excellent detector coverage at the HIPPO beamline at Los Alamos, our neutron scattering data has a time resolution of the order of minutes, allowing us to follow the changes in real time. We find that the response of the Bragg-scattering crystal grains occurs quickly, on the timescale of thermal diffusivity, while the macroscopic elasticity responds slowly, on scales longer by orders of magnitude. This nonclassical nonlinear behavior is due to a component in the rocks which is either amorphous (no coherent Bragg scattering) or has a volume too small for detection. The bond/contact system in the rock may fill both these requirements. Work supported by Los Alamos Directed Research &Development funds and by the Office of Basic Energy Sciences, Geosciences.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMNG31C1608D
- Keywords:
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- 4494 Instruments and techniques