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Increasing the Versatility of the G. E. Diffractometer

Published online by Cambridge University Press:  06 March 2019

L. H. Schwartz ,
L. A. Morrison  and
J. B. Cohen
L. H. Schwartz
Affiliation:
Materials Research Center and Department of Materials Science, The Technological Institute, Northwestern University, Evanston, Illinois
L. A. Morrison
Affiliation:
Materials Research Center and Department of Materials Science, The Technological Institute, Northwestern University, Evanston, Illinois
J. B. Cohen
Affiliation:
Materials Research Center and Department of Materials Science, The Technological Institute, Northwestern University, Evanston, Illinois
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Abstract

To achieve increased case and precision of alignment, and to allow for convenient alteration between normal usage with filtered radiation and crystalmonochromated radiation, the G. E. goniometer has been mounted on milling machine beds allowing for x-y translation and 360° rotation; in addition the tube mount was repositioned. The usefulness of this apparatus has been demonstrated by accurately aligning the goniometer for usage with filtered radiation, with a new alignment procedure. As a demonstration of the accuracy and precision of alignment, the lattice parameter of silicon was determined from a powder sample. A least-squares analysis of the data gave a0 = 5.43046 Å with a standard deviation of ±0.00005 Å, in excellent agreement with the value of 5.43054 ± 0.00017 Å determined in a recent International Union of Crystallography test in many laboratories.

A monochromator housing has been built for use with all types of direct-beam monochromators and all radiations. This apparatus attaches to the new tube mount and was used to determine the optimum procedure for preparing the doubly bent LiF monochromator crystals designed by Warren to minimize the volume sampled in the reciprocal space of a single crystal. According to a suggestion made by Chipman, a doubly bent monochromator for use with poly crystalline specimens has been formed and its geometry and applications are presented. This monochromator gives about one-half as much intensity as that obtainable using filtered radiation and similar operating conditions ; this type of monochromator is therefore a powerful tool for use with powder specimens. A transmission diffracted-beam monochromator has also been constructed which attaches in a simple manner under the counter tube housing. Under similar operating conditions with a LiF monochromator, this yields intensities only one-tenth of those obtained using filtered radiation.

Type
Research Article
Information
Advances in X-Ray Analysis , Volume 7: Twelfth Annual Conference on Applications of X-ray Analysis, August 7-9, 1963 , 1963 , pp. 281 - 301
Copyright
Copyright © International Centre for Diffraction Data 1963

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References

page 283 note * This goniostat allows for a rotation to about an axis perpendicular to the plane containing the incident and diffracted beams, a rotation x about an axis parallel to this plane and a rotation ϕ about an axis which is perpendicular to the x axis and which can vary from parallel to perpendicular to this plane. Motions described can be readily achieved without the expense of the goniostat, or new table. The x-y motion can be obtained by temporarily fastening large bolts (to the G. E. table), which push on the base plate. The x and ϕ rotations can be achieved with, the normal powder sample holder by opening the bolt holes that hold the knife edges and inserting strong springs. The 180° rotation described in. step 3 requires only that the normal sample holder be replaced in its 180° position.

page 283 note † This attachment was originally suggested to us by Prof. C. N. J. Wagner of Yale University.

1 References are at the end of the paper.

page 284 note * This step is essentially the same as that recommended in the alignment procedures for the Picker difixactometer.

page 284 note † The silicon powder was 99.9% Si, in the form of a pressed briquette. No residual stresses could be detected. The powder came from the same supplier as that used in the L.U.Cr. test.

page 288 note * With doubly bent monochromators, the spot focus of the X-ray tube is used; in this study, with filtered radiation of the transmitted beam monochromator, the line focus was used

page 289 note * Details of the design are given in the Appendix.