Detection of atoms using monochromatic X-rays

A method according to clam 8, wherein the secondary radiator is a disc arranged for rotation about its axis and the areas are spaced circumferentially about the axis so that upon rotation of the disc the areas are exposed alternately to X-rays thereby alternately to expose the specimen to secondary radiation from the one and another areas.

Apparatus for detecting, in a specimen, atoms, of a particular element having an atomic number of at least 20, comprising a source of monochromatic X-rays having a wavelength to induce an inner shell ionization of said atoms with subsequent auger cascade, and means for detecting the auger electrons emitted by the cascade, wherein the source is adapted to irradiate the specimen alternately with X-rays of said wavelength and with X-rays of a wavelength less than said wavelength and means are adapted to determine the difference between auger electrons detected at said wavelength and at the shorter wavelength.