Micro-analysis by a Flying-Spot X-Ray Method

THE point-by-point investigation of a surface by analysis of the characteristic X-ray line emission has been initiated by Castaing1. He obtained an electron spot of the order of 1 micron in diameter with an electrostatic lens system and moved the specimen under the fixed spot; the point examined was identified by means of an optical viewing system. Analysis is greatly facilitated if the electron spot is scanned across the specimen and if a counter is used for collecting part of the emitted X-rays. The signal from it can be transferred to a cathode-ray tube scanned in synchronism, so that a picture is displayed of the part of the surface under investigation. Such a system is similar to the electron scanning microscope2. It differs appreciably from that proposed by Pattee3, in which an electron spot scans a thin target of a pure metal next to which is placed the specimen to be examined, so that image contrast is due not to emission but to differential absorption, as in the normal form of X-ray projection microscope4.