Neutron diffraction

Intracrystalline strain measurement on geological materials using neutron diffraction

 

Investigations within the "Agreement between the Ministry for Education and Research of the Federal Republic of Germany (BMBF) and the Joint Institute for Nuclear Research (JINR) in Dubna (Russian Federation) concerning cooperation and exploitation of facilities and services of the JINR"
and
the correspondent agreement between the Frank-Laboratory of Neutron Physics and the GeoForschungsZentrum (GFZ) Potsdam

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A team of physicists, geologists and mathematicians from the GFZ Potsdam took over a diffractometer (Epsilon) for intracrystalline strain measurements in April 1997. This facility was a temporary model using neutron diffraction - especially the time-of-flight method - for experiments on rock-forming minerals, i.e. geological materials. The diffractometer is located at beam line 7A of the pulsed research reactor IBR-2 of the in Dubna (Russian Federation).

The aim of this research is a better understanding of deformation processes, which take place in rocks under conditions of the Earth's upper crust (down to about 10 km depth). Emphasised are in-situ observations of macro- and microstresses in rocks depending on increasing or decreasing applied load as well as the role of residual stress states. The main topics to be studied are strain-stress distributions as the reason for the formation of textures, the consequences of superimposed deformations, the problems of stress redistribution and the texture-dependent residual strain-stress states of rocks.

Following this concept the experimental setup Epsilon was at first completed by the deformation device Exstress. The combination Epsilon-Exstress permits studies on rocks under variable applied load (up to 150 MPa). First experiments were carried out on monomineralic, untextured rocks (sandstone, dolomite) combined with residual stress determinations. Afterwards, olivine-quartz and dunite-quartzite samples were studied using neutron as well as synchrotron radiation, including strain scanning across borders of deformed and different rocks.

From the results of the first experiments followed the necessity to rebuild the diffractometer Epsilon in order to achieve a substantial reduction of measuring time. Therefore, since 1999 a completely new instrument including controlling software has been designed and commissioned in May 2001. Epsilon-MDS is a multidetector instrument, equipped with radial collimators and permits the simultaneous measurement of the lattice spacings without any movements of the sample.

The team maintains scientific contacts using similar instruments in different institutes.

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Contact:
Dipl. Geol. Dr. habil. A. Frischbutter
GeoForschungsZentrum (GFZ) Potsdam
e-mail: fribu@gfz-potsdam.de

Dipl. Phys. Dr. Christian Scheffzük
GeoForschungsZentrum (GFZ) Potsdam, c/o Joint Institute of Nuclear Research (JINR) Dubna
e-mail: cscheff@nfsun1.jinr.ru
scheff@gfz-potsdam.de

Math. Roman Shukov
Universität Tula; c/o Joint Institut of Nuclear Research (JINR) Dubna

Dipl. Phys. Dr. Kurt Walther
GeoForschungsZentrum (GFZ) Potsdam, c/o Institut für Geophysik der TU Bergakademie Freiberg
e-mail: walter@gfz-potsdam.de
Kurt.Walther@geo.tu-freiberg.de