A Short Wave X-Ray Spectrograph and Some K Series Emission Wave-Lengths

Transmission type spectrograph for short x-rays.—The spectrograph described is similar to that used by Rutherford and Andrade for $\gamma$ rays. A calcite plate 1.6 mm thick ground with the faces perpendicular to the (100) planes was placed midway between two slits, through one of which (3 mm wide) it was illuminated with x-rays from the source, and through the other (.15 mm wide) the rays reflected from (100) planes on both sides of the axis passed to the photographic plate. A strip of lead at the middle of the crystal intercepted the direct beam. The advantages of this spectrograph are (1) that all uncertainty as to the depth of penetration into the crystal is eliminated; (2) lines are obtained whose sharpness is independent of the distance of the photographic plate; (3) all the lines of the K series are obtained simultaneously without crystal rotation; and (4) the time of exposure may be greatly reduced by placing the crystal close to the source of the rays.