Increasing the Versatility of the G. E. Diffractometer

Abstract

AbstractTo 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.