Chalk River Workshop on Neutron Powder Diffraction

The DUALSPEC powder diffractometer at the National Research Universal (NRU) reactor of Atomic Energy of Canada Limited (AECL) Research is one of the most powerful instruments available for making neutron powder diffraction measurements. In May, 1994, the Neutron and Condensed Matter Science Branch of Chalk River Labs hosted a Workshop on Neutron Powder Diffraction, organized by B. M. Powell (AECL) and B. H. Torrie (Waterloo). Workshop instructors covered the topics of powder profile refinement (A. P. Wilkinson, Georgia Tech), DUALSPEC powder diffractometer operation and performance (B. M. Powell, Chalk River), implementation of rigid body constraints in refinement (I. P. Swainson, AECL), joint refinement of neutron and X-ray powder data (R. B. Von Dreele, LANL), special attributes of neutron powder diffraction in certain applications (B. H. Torrie), and ab initio structure solution from powder data (A. P. Wilkinson). It has been demonstrated that joint refinement of neutrons and X-ray diffraction data can lead to more precise atomic parameters, reduce uncertainty and impose greater restrictions on a model and make the variables more independent in the least squares fitting.

A workshop on Neutron Applications in Material Science and Engineering was held in Chalk River in August 1994. The workshop focused on application of fundamental techniques to industrial problems. In neutron scattering techniques, the neutron beam is scattered by the atoms in the sample, and in absorption techniques the beam is absorbed by the atoms and an emitted particle is registered in a detector. Either constant wavelength or time-of-flight, scattering techniques are used for phase identification, microstructural investigations, and residual stress and texture determination. The field of small angle scattering as applied to metallurgy, ceramics, polymers and porous material, such as prototype insulators or oil shales, was covered in a series of four lectures. Two lectures were devoted to the new field of reflectometry which probes, by scattering, the near-surface region of materials over depths of 10-1000 Å. One lecture was devoted to materials science studies by inelastic neutron scattering. Absorption techniques included depth profiling of certain atomic species such as helium, nitrogen and boron, gamma analysis for geological studies and hydrogen assay, and neutron activation analysis. Finally the state of the art in neutron radiography was reviewed.

The seminar speakers were drawn from the National Institute for Standards and Technology, Los Alamos, Oak Ridge and Sandia National Labs in the US and from McMaster University, Dalhousie University and Chalk River Labs in Canada. The workshop was sponsored by the Canadian Institute for Neutron Scattering, the Neutron Scattering Society of America, and the Natural Sciences and Engineering Research Council with support from AECL Research, Natural Sciences and Engineering Research Council of Canada, the National Institute for Standards and Technologyand Los Alamos National Lab.