Authors: Jens M. Walter, for others see text body (not enough space)

Abstract
Hans Boysen, Donald Bruce Dingwell, Agust Gudmundsson, Bent T. Hansen, Kai-Uwe Hess, Bernd Leiss, Wolfgang Schmahl, Michael Stipp

Within the past years, neutron texture analysis has become a routine tool in geo- and materials sciences. Many projects were carried out and are actually in progress, concerning e.g. the fabric development in mono- and polyphase rocks, deformation histories and kinematics during mountain building processes and the quantitative characterization of anisotropic physical properties, both in natural rocks as well as in experiments with natural or model materials (see e.g. contribution of Leiss and Schmahl). The resulting need of an increase in measuring time for geomaterials is counteracted by the shutoff of the research reactor FRJ-2 in Jülich at the end of April 2006. Additional shutoffs of other research reactors are in discussion.

The new ‘Osthalle’ at FRM-II, which is currently under construction, offers the unique chance to build up a new TOF-diffractometer (GeoDiffractometer) in combination with additional experimental instrumentations of geoscientific purpose(see e.g. contribution of Keppler). In the external Osthalle a flight path of about 35 m can be realized. As geological material is often characterised by fairly coarse-grained mineral phases where low symmetries are common, a beam-size of about 3 to 4 cm in diameter is necessary and a broad range of d-values must be measurable. The instrument should be optimized for a high flux and a medium to high resolution to measure also series of geological samples in reasonable measuring times. Short measurement times are achieved by a high neutron intensity at the sample (high flux) and by minimal sample rotation in a time-of-flight (TOF) setup. Large sample series need to be measured due to the heterogenous material in complex geological situations, e.g. polyphase deformed lithosphere. Together with the high neutron flux and a large beam size, the instrument would offer ideal measuring conditions for geological samples and most materials in materials science.

The uniqueness of this measuring set-up is the combination of a TOF-diffractometer with different sample environments for static and deformation experiments (stress and strain). A HT/MP deformation apparatus is planned, to allow in-situ measurements of the texture development during deformation and annealing, as well as a LP/LT or atmorspheric-P deformation rig for in-situ deformation experiments on ice, halite or rock analogue materials. Additionally, an uniaxial stress frame for in situ stress investigations is planned. The TOF-technique will allow simultaneous measurements of stress, elastic or plastic deformation and texture. Furthermore a HT/HP-autoclave is planned for glass and melts investigations combined with radiography for investigations on shear viscosities, shear instabilities and phase separations.

The concept is complementary to the texture diffractometer in Dubna, Russia and the Stress Diffractometer STRESS-SPEC in Munich. For powder diffraction the diffractometer will be complementary to the powder diffractometer SPODI, offering the possibility of short, high intensity parametric measurements which should be conducted in dependency of temperature, electrical, magnetic and stress fields due to lower resolution but higher flux at the sample.