Design of a Double-Crystal X-Ray Vacuum Spectrometer

Abstract

A vacuum double-crystal x-ray ionization spectrometer has been constructed and the design of the instrument is explained in some detail. A tank, of inside diameter 50 cm, formed from sheets of rolled steel and welded together, rests on a thick steel bedplate, the contact areas, generously wide, sealed with stop-cock grease, and the chamber evacuated with a magavac oil pump. This chamber is used as the forevacuum for the Hg condensation pump working on a metal x-ray tube. The slits, the first and second crystals, and the ionization chamber are contained within the tank. The axes of the two crystals are rigidly fixed with respect to each other, and, to allow change of wave-length, the x-ray tube, clamped to the side of the tank, is swung around, the tank sliding on the stop-cock grease, until the proper position is reached. Final alignment of the focal spot with the slits is effected while the tube is in operation by an adjustable target made possible by a sylphon connection in the tube. A method is explained for obtaining thermal contact with uranium for use as the target. The angular controls of the crystal $B$ and the ionization chamber are made by having long, concentric, tapered bearings extend through the bed-plate of the instrument, lubricated and held air tight with stop-cock grease, and their positions read to within one minute of arc with verniers on a fixed circle. Fine motion of crystal $B$ is accomplished by the usual lever arm and tangent micrometer screw. The insulated lead from a relatively small ionization chamber, 6.7 cubic inches in volume, which is constructed to function as a two-atmosphere pressure chamber, is brought out of the tank through the hollow center of the central steel shaft forming the axis of crystal $B$.