ISSN:1044-8632    

DOI:10.1080/10448639508217669

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639508217670

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639508217671

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The DUALSPEC powder diffractometer at the NRU reactor of AECL Research is one of the most powerful instruments available for making neutron powder diffraction measurements. Its major feature is an 800-wire, curved, position-sensitive detector. The radius of the detector is 1.5 m and the angular separation of the wires is 0.1°. The detector thus collects data simultaneously over an 80° range of scattering angles. The complete range of scattering angles (120°) is covered by setting the detector in low and high angle positions. It may also be stepped between wires in steps as small as 0.01°. An oscillating radial collimator is positioned before the detector to suppress unwanted background from the sample environment. The specimen may be continuously rotated or may be oscillated through a specified angular range as the experiment requires and an XY translational table permits precise centering of the specimen. The maximum instrumental resolution (Δd/d) is 0.12 percent. A wide variety of monochromators are available, including a focusing monochromator for Si(531) planes. The monochromator take-off angle is continuously variable from 15° to 120°. The introduction of this state-of-the-art diffractometer as a user facility in mid-1992 led to a great increase inthe number of scientists wishing to utilize neutron powder diffraction methods as part of their research programs. But many were unfamiliar with the detailed application of the technique. As part of a continuing program to train students in the application of this neutron scattering; technique, the Neutron and Condensed Matter Science Branch of Chalk River Laboratories recently hosted a 2nd Workshop on Neutron Powder Diffraction. Sponsored by the Canadian Institute for Neutron Scattering, the Natural Sciences and Engineering Research Council and by AECL Research, the workshop was organized by Brian M. Powell (AECL) and by B.H. Torrie (Waterloo) on May 26–27 at Chalk River Laboratories. Twenty students from across Canada heard formal lectures on the technique and its applications each morning, while in the afternoons “hands-on” analysis of neutron diffraction data was carried out. The students also toured the DUALSPEC facility at the NRU reactor.

ISSN:1044-8632    

DOI:10.1080/10448639508217672

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639508217673

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639508217674

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

It is widely accepted that the preeminent technique for the determination of the structure of biological macromolecules is X-ray crystallography. For the solution of structures at near atomic resolution, it has for many years been the only technique, although recently a number of structures of low molecular weight (< 25000) have been solved by NMR. A handful of structures has also been investigated at high resolution by neutron crystallography, but in these cases the X-ray structure was already known and neutrons were used to obtain complementary information on the positions of important protons in the macromolecule or on the surrounding water molecules. Despite the success of the X-ray techniques, there exist, however, a number of cases, in particular of large macromolecular assemblies, where high resolution information cannot be obtained for at least part of the structure even though highly diffracting crystals exist. It is often one particular chemical component or part of a molecule that cannot be seen with X-rays. This is usually due to the fact that these components are at least partially disordered in the crystal. Some examples are the nucleic acid in spherical viruses, the DNA in nucleosome core partkles, the lipid in lipoproteins and detergent in crystals of detergent solubilized membrane proteins.

ISSN:1044-8632    

DOI:10.1080/10448639508217675

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

One of the trade-off qualities of neutrons is their capability to penetrate matter even up to several centimeters, thus, neutron scattering techniques provide us with microscopic information onbulkcompositional, structural and magnetic order, as well asbulkexcitations. Unwanted surface effects don't contribute.

ISSN:1044-8632    

DOI:10.1080/10448639508217676

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639508217677

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639508217678

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor