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| Titel |
POWTEX Neutron Diffractometer at FRM II - New Perspectives for In-Situ Rock Deformation Analysis |
| VerfasserIn |
J. M. Walter, M. Stipp, K. Ullemeyer, H. Klein, B. Leiss, B. T. Hansen, W. F. Kuhs |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250070939
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| Zusammenfassung |
| In Geoscience quantitative texture analysis here defined as the quantitative analysis of the
crystallographic preferred orientation (CPO), is a common tool for the investigation of fabric
development in mono- and polyphase rocks, their deformation histories and kinematics. Bulk
texture measurements also allow the quantitative characterisation of the anisotropic physical
properties of rock materials. A routine tool to measure bulk sample volumes is neutron
texture diffraction, as neutrons have large penetration capabilities of several cm in geological
sample materials.
The new POWTEX (POWder and TEXture) Diffractometer at the neutron research reactor
FRM II in Garching, Germany is designed as a high-intensity diffractometer by groups from
the RWTH Aachen, Forschungszentrum Jülich and the University of Göttingen.
Complementary to existing neutron diffractometers (SKAT at Dubna, Russia; GEM at ISIS,
UK; HIPPO at Los Alamos, USA; D20 at ILL, France; and the local STRESS-SPEC and
SPODI at FRM II) the layout of POWTEX is focused on fast time-resolved experiments
and the measurement of larger sample series as necessary for the study of large
scale geological structures. POWTEX is a dedicated beam line for geoscientific
research.
Effective texture measurements without sample tilting and rotation are possible firstly by
utilizing a range of neutron wavelengths simultaneously (Time-of-Flight technique) and
secondly by the high detector coverage (9.8 sr) and a high flux (~1 Ã 107 n/cm2s) at the
sample. Furthermore the instrument and the angular detector resolution is designed also for
strong recrystallisation textures as well as for weak textures of polyphase rocks. These
instrument characteristics allow in-situ time-resolved texture measurements during
deformation experiments on rocksalt, ice and other materials as large sample environments
will be implemented at POWTEX.
The in-situ deformation apparatus is operated by a uniaxial spindle drive with a maximum
axial load of 250 kN, which will be redesigned to minimize shadowing effects inside the
cylindrical detector. The HT deformatione experiments will be carried out in uniaxial
compression or extension and an upgrade to triaxial deformation conditions is envisaged. The
load frame can alternatively be used for ice deformation by inserting a cryostat cell for
temperatures down to 77 K with a triaxial apparatus allowing also simple shear
experiments on ice. Strain rates range between 10-8 and 10-3 s-1 reaching to
at least 50 % axial strain. The deformation apparatus is designed for continuous
long-term deformation experiments and can be exchanged between in-situ and ex-situ
placements during continuous operation inside and outside the neutron detector. |
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