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The application of neutrons to study the crystal structures of powdered minerals is of growing popularity among earth scientists. This has just recently been demonstrated at a workshop on Neutrons at the Frontiers of Earth Sciences and Environments (NESE) (Rinaldi and Schober 2006).
There are a number of physical reasons to study minerals with neutrons. They are related to the fundamental properties of neutrons regarding their interaction with matter (Parise 2006a, this volume). The major points are the isotope specific scattering lengths and absorption cross-sections of the neutron, being independent of the number of electrons. The scattering power of many elements is of similar magnitude (see Table 1⇓ for some elements of interest for minerals). As a consequence neutrons are well suited to localize light elements (also in the direct neighborhood of heavy elements) and to distinguish between ions or atoms having the same or a very similar number of electrons. A large advantage of neutrons over X-rays is the independence of the scattering power of the scattering angle. Consequently, structural data from neutron experiments are in principle of higher precision.
The focus of this Chapter is on powder diffraction. There are several answers to the question why to study powders. The material may not be available as a single crystal or cannot be grown to the appropriate size. Since the interaction potential of neutrons with matter is small, single crystals should be in the order of about 1 mm3 (Ross and Hoffman 2006, this volume). Many natural samples are multi phased or structurally and chemically heterogeneous. In order to measure a …