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Single-crystal Neutron Diffraction: Present and Future Applications

Crystallography Laboratory, Department of Geosciences Virginia Polytechnic Institute and State University Blacksburg, Virginia, 24061, U.S.A., e-mail: nross@vt.edu

Christina Hoffmann

Oak Ridge National Laboratory/SNS, One Bethel Valley Road, P.O. Box 2008, MS6474, Oak Ridge, Tennessee, 37831-6474, U.S.A. e-mail: hoffmanncm@ornl.gov

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
Single-crystal neutron diffraction provides a powerful complementary probe to X-ray diffraction for the characterization of earth materials. The ability of neutron diffraction to determine the position of the atomic nucleus rather than electron density is key to its use in structural studies. A typical neutron beam spectrum contains neutrons in the energy ranges of epithermal, hot, thermal and cold. The relation between the neutron kinetic energy and the wavelength is:

(1)

where m is the neutron mass and v is the velocity. This can be transformed in (1) via de Broglie using the Plancks constant, , and the wavelength, . This equation is frequently used in neutron diffraction to convert energies (E) into wavelengths that directly describe the useful experimental range:

(2)

Conventional ranges for neutron energies and corresponding wavelengths for neutron scattering experiments are:

1. "epithermal neutrons E > 500 meV = 0.5 Å
   
2. "hot" neutrons E = 100–500 meV = 0.5–1 Å
   
3. "thermal" neutrons E = 10–100 meV = 1–3 Å
   
4. "cold" neutrons E = 0.1–10 meV = 3–30 Å
   

Cold neutrons are used for macromolecular crystallography (3–10 Å) and hot neutrons are typically used for high resolution measurements, magnetic form factor studies, and amorphous materials. Single-crystal neutron diffraction typically uses thermal to hot neutrons for small and medium-size unit cells < 25 Å per unit cell basal vector (approx. 0.5–7 Å).

This chapter presents a summary of some of the applications to which single-crystal neutron diffraction has been put in the study of earth and related materials, together with an account of the techniques and instrumentation used for these experiments. Recent developments in instrumentation, and the new scientific applications that have resulted from these, are described along with a forward look to some of the exciting developments currently taking place in this field.

	REACTOR SOURCES AND SINGLE-CRYSTAL INSTRUMENTATION

 
As described in Vogel and . . . [Full Text of this Article]

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