Author: Bjoern Winkler Institut für Geowissenschaften, Abt. Kristallographie,Johann Wolfgang Goethe Universität,Senckenberganlage 30

Abstract
Neutron diffraction, i.e. coherent elastic neutron scattering, is a well established technique for structural studies of geomaterials. In contrast to this, other neutron scattering techniques have only rarely been applied to study properties of minerals, although undoubtedly such studies would provide insight not attainable otherwise. These other neutron scattering techniques, such as inelastic coherent scattering, inelastic incoherent scattering, inelastic magnetic scattering, are all well established in the solid state physics community. Hence, the expertise available there can readily be transferred and this will open up new research opportunities and provide new understanding in the Earth Sciences.

Inelastic coherent scattering on single crystals is a unique way to study the lattice dynamics, as this techniques allows to determine the phonon dispersion. An outstanding success of this technique was the clarification of the origin of the incommensurate phase which occurs in a small temperature interval between the α- an the β-phase of quartz. Only very few studies on complex silicates have been published (see e.g. summary in Dove, 1993). The phonon density of state can be obtained from powder measurements by inelastic coherent measurements. Such measurements require long counting times and there is a problem of correcting for multiple scattering at high frequencies, and this has limited the number of studies.

Inelastic and quasielastic incoherent scattering is a technique which is very well suited to
study the dynamics of hydrogen, and hence of H2O molecules, in minerals (Winkler, 1999). By this technique, it can be shown if there is translational or rotational diffusion of molecules in zeolites, and whether or not the molecular dynamics of a water molecule couple to the lattice dynamics. In addition to studies of zeolites and layer minerals, this approach has been relevant for the understanding of the molecular dynamics in cordierite and in gypsum and its dehydration products.

Inelastic magnetic scattering allows to measure electronic transitions in transition metalcontaining minerals. This field, up to now, is dominated by optical spectroscopy (Burns, 1993), and neutron spectroscopy will provide access to complementary energy ranges (e.g. Winkler et al., 1997).

Small angle neutron scattering studies have also only be used by very few groups to
characterize the microstructure of bulk rocks. These studies (see e.g. summary in Kahle et al., 2004) have shown a surprising self-similarity of the microstructure over many orders of magnitude, but due to the absence of any in situ studies, virtually nothing is known about the influence of formation conditions on the microstructure.

Another field which certainly will gain in importance is neutron radiography and
tomography. The complementarity of neutron radiography and x-ray radiography can be
exploited on modern radiography/tomography stations such as the ANTARES facility at the FRM II. Specifically for the observation of processes, such as magma mingling or the
degassing of melts, neutron radiography seems to be an ideal tool, which has not been
exploited at all.

The few examples given above already show a large variety of techniques which remain to be applied to problems in the Earth Sciences. This list is far from being complete (e.g. it doesn’t include spin-echo investigations, deep inelastic scattering, neutron resonance absorption, etc). As all these experimental approaches offer insight into properties of minerals which cannot be obtained otherwise, or which complement other approaches, clearly there is a need to make this opportunities known to the geoscience community.

References
Burns RG (1993) Mineralogical Applications of Crystal Field Theory. Cambridge University Press.
Dove MT (1993) Introduction to lattice dynamics. Cambridge University Press
Kahle A, Winkler B, Radulescu A, Schreuer J (2004) Small-angle neutron scattering study of volcanic rocks. European Journal of Mineralogy, 16, 407-417
Winkler B, Harris MJ, Eccleston RS, Knorr K, Hennion B (1997) Crystal field transitions in Co2[Al4Si5]O18 cordierite and CoAl2O4 spinel determined by neutron spectroscopy.
Physics and Chemistry of Minerals, 25, 79-82
Winkler, B (1999) Introduction to the application of neutron spectroscopy in the Earth
Sciences. In: Wright, K and Catlow, R (eds) microscopic Properties and Processes in
Minerals. Kluwer Academic Publishers, 93-144.