title: Submicrometer hyperspectral X-ray imaging of heterogeneous rocks and geomaterials: applications at the Fe k-edge.
abstract: Because of their complex genesis, rocks and geomaterials are commonly polycrystalline heterogeneous systems, with various scale-level chemical and structural heterogeneities. Like most other μ-analytical techniques relying on scanning instruments with pencil-beam, the X-ray absorption near edge structure (XANES) technique allows elemental oxidation states to be probed with high spatial resolution but suffers from long acquisition times, imposing practical limits on the field of view. Now, regions of interest of sample are generally several orders of magnitude larger than the beam size. Here, we show the potential of coupling XANES and full-field absorption radiographies with a large hard X-ray beam. Thanks to a new setup, which allows both the acquisition of a XANES image stack and the execution of polarization contrast imaging, 1 to 4 mega-pixel crystallographic orientations and Fe oxidation state mapping corrected from polarization effects are obtained in a couple of hours on polycrystalline materials with submicrometric resolution. The demonstration is first carried out on complex metamorphic rocks, where Fe(3+)/Fe(total) images reveal subtle redox variations within single mineralogical phases. A second application concerns a bentonite analogue considered for nuclear waste and CO(2) storage. Proportion mappings of finely mixed phases are extracted from hyperspectral data, imaging the spatial progress of reaction processes essential for the safety of such storage systems.
authors.affiliation: European Synchrotron Radiation Facility, ID21 beamline, BP220, 38043 Grenoble Cedex, France. vdeandrade@bnl.gov
authors.forename: Vincent
authors.initials: V
authors.lastname: De Andrade
authors.forename: Jean
authors.initials: J
authors.lastname: Susini
authors.forename: Murielle
authors.initials: M
authors.lastname: Salomé
authors.forename: Olivier
authors.initials: O
authors.lastname: Beraldin
authors.forename: Cecile
authors.initials: C
authors.lastname: Rigault
authors.forename: Thomas
authors.initials: T
authors.lastname: Heymes
authors.forename: Eric
authors.initials: E
authors.lastname: Lewin
authors.forename: Olivier
authors.initials: O
authors.lastname: Vidal