An experimental X-ray shadow microscope

A source of X-rays smaller than 0·5μ in diameter is produced by means of magnetic electron lenses and used for projecting shadow images, mainly of insects opaque to visible light. A resolving power approaching that of the optical microscope is obtained with dried specimens; with living organisms the resolution is less. The use of a Lenard window as X-ray target allows high intensity at the specimen and exposure times in the order of minutes at useful primary magnification. Consideration of the practical limitations on resolution, contrast and exposure shows that an ultimate resolution of 100Å should be possible with an exposure of 1 h. Other uses of such a point source are indicated, in addition to shadow radiography.