Focusing of an X-Ray Beam by a Rocksalt Crystal

A single crystal of rocksalt (halite) has been bent plastically and cut so that x-rays of a narrow range of wave-lengths coming from the focal point of the x-ray tube, are focused at another point. In this way the divergent beam from the x-ray tube (about 6° divergence) is monochromatized and concentrated so that the intensities of the Fe $K\alpha$ lines are about 30 times as great as when monochromatized by reflection from a plane crystal. The point of focus was placed on the reflection circle of a Seeman-Bohlin focusing camera and powder photographs were taken, the advantage over the usual arrangement being that the background (due to undesired wave-lengths) is much diminished without any serious loss of intensity in the lines.