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| Titel |
POWTEX Diffractometer at FRM II - New Perspectives in Geoscientific Neutron Diffraction |
| VerfasserIn |
Jens Walter, Andreas Houben, Werner Schweika, Michael Stipp, Klaus Ullemeyer, Helmut Klein, Bernd Leiss, Bent T. Hansen, Werner F. Kuhs |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057589
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| Zusammenfassung |
| In recent decades neutron diffraction has become a commonly used method in Geoscience for
the quantitative analysis of crystallographic preferred orientations (CPOs) and for
experimental high-field powder diffraction in respect to pressure, temperature, magnetic and
electric fields. Quantitative texture analysis with neutrons is now also a routine tool for the
investigation of fabric development in mono- and polyphase rocks, deformation histories and
kinematics during mountain building processes and the characterization of flow kinematics in
lava flows. Furthermore the quantitative characterization of anisotropic physical
properties of both rock and analogue materials by bulk texture measurements can
be achieved by neutron diffraction due to the high penetration capabilities of the
neutrons.
To cope with the geoscientific needs for increased beam time at neutron diffraction
facilities with the corresponding technical characteristics and equipment, POWTEX
(POWder and TEXture Diffractometer) at the neutron research reactor FRM II in
Garching, Germany is designed as a high-intensity diffractometer by a consortium of
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 the POWTEX diffractometer is focused
on fast measurements for either time-resolved experiments or the measurement
of larger sample series as necessary e.g. for the study of large scale geological
structures. This is possible due to the simultaneous utilization of a range of neutron
wavelengths by means of the time-of-flight technique with a high flux of about 1 x 107
n/cm2s and a large detector coverage of 9.8 sr. The detector layout will provide a
sufficient angular resolution and pole figure coverage to be able to measure strong
recrystallisation textures as well as weak textures of polyphase rocks without the
necessity of sample tilting and rotation. This instrument configuration allows large
sample environments, which will be implemented at POWTEX allowing in-situ
time-resolved texture measurements during deformation experiments on rock salt,
carbonates, ice and other materials. Furthermore a furnace for 3D-recrystallisation
analysis by orientation stereology of the single grains will be built for POWTEX
corresponding to the furnace that already exists for fine grained materials at the
synchrotron beamline BW5 at HASYLAB, Germany (e.g. Klein et al. 2009 and references
therein).
The in-situ triaxial deformation apparatus is operated by a uniaxial spindle drive with a
maximum axial load of 200 kN, which will be specially designed to minimize shadowing
effects between the sample and the neutron detector. The high temperature experiments will
be carried out in uniaxial compression or extension at temperatures up to 1200Ë C 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. The
spindle drive will be suitable for strain rates ranging between 10-8 and 10-3 s-1
reaching to at least 50 % axial strain. The furnace for the recrystallization analysis
will be a mirror furnace with temperatures up to 1500Ë C, which will be rotatable
around a vertical axis to obtain the required stereologic orientation information. This
furnace can also be used as a standard furnace for parametric HT powder diffraction
experiments.
References:
Klein, H. (2009). Principles of highly resolved determination of texture and
microstructure using high-energy synchrotron radiation. Adv. Eng. Mat. 11, 452-458. |
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