Herbert W. Schnopper

A combined focusing X-ray diffractometer and nondispersive X-ray spectrometer for lunar and planetary analysis.

An instrument is described which is intended to perform a dual purpose (elemental—structural) analysis consistent with the environmental conditions implied by lunar or planetary operation. The diffractometer section is based on a modified Seeman—Bohlin focusing principle in which a sharp-line focus target, a powdered sample, and a movable detector slit all lie on the focusing circle. The convolution of the projections on the focal circle, of a narrow receiving slit on the detector, the line focus target, combined with a high dispersion produce higher resolution and intensity than is common with Bragg focusing diffractometers with similar instrumental parameters. The range of d-spacings covered is from 1 to 7 A (chromium target). The chemical analysis section of the instrument utilizes the fluorescent X-rays produced in the specimen by the primary beam. A proportional counter and pulse-height analyzer accomplish detection and energy discrimination. Resolution is low, but the analysis can distinguish between elements in the range of atomic numbers 11 to 29. Data from a breadboard model is presented. The entire unit, although primarily intended to meet the requirements of space, performs equally well as a routine laboratory analyzer. The horizontal, stationary nature of the specimen holder suggests several specific applications.

Erratum: Spectral Measurements with Aligned and Misaligned Two‐Crystal Spectrometers. II. Alignment

Conditions for and methods of aligning a two‐crystal spectrometer are discussed. These include the alignment of rotation axes, crystals, and x‐ray beam. The results of a new nondispersive crystal alignment procedure are compared in detail with theory for a typical case of CuKα radiation and calcite crystals. This method is contrasted with other procedures which lead only to pseudo‐alignments.It is shown that x‐ray methods which are sensitive to vertical divergence do not lead to crystal alignment unless the beam is already perfectly aligned. It is concluded that the x‐ray beam can be aligned only after the crystals have been aligned.