Preparation of high purity beryllium foils

Abstract

A technique is described f> the preparation of beryl liu;;i foils by vapor deposition. The hitjh-purity, pinhoie-free foils are v.icimn tight and suitable for nany x-ray analysis applications. The beryllium is evaporated from an electron heai'i healed crucible source onto a heated substrate. Substrate temperatures of 4bO to 700°C are necessary to obtain the desired mechanical properties of thp foi!s. At these temperatures, contamination of the foils by diffusion of the substrate material into the beryllium can be a significant problem, as impurity levels of more than several hundred ppro arc detrimental to the x-ray transparency of the windows. This problem is minimized by careful selection and preparation cf the substrate. A clean deposition system and pure source naterial are necessary to preserve elemental integrity of the vapor-deposited foils.