X-ray tube and X-ray fluorescence analyser utilizing selective excitation radiation

An X-ray tube having a structure decreasing an amount of soft bremsstrahlung that reaches a sample to be analysed, comprising:

• a cathode that provides a source of electrons with kinetic energy;
• an anode with an electron receiving surface that, in use, generates hard bremsstrahlung where the electrons hit the electron receiving surface, the electron receiving surface being a layer of anode material that generates hard bremsstrahlung, the anode comprising the layer of anode material directly on top of a block of attenuator material deeper in the anode than said layer of anode material in the arrival direction of the electrons, wherein the atomic number of said attenuator material is less than one third of the atomic number of the anode material;
• and
• a window facing the electron receiving surface of the anode so that at least some of the generated hard bremsstrahlung from the surface of the anode where the electrons hit have a direct propagation path to and out of the window to the sample to be analysed,
• wherein a thickness of the layer of anode material is sufficiently thin such that a majority of the hard bremsstrahlung will be generated in the layer of anode material and most of the electrons that do not lose a large majority of the kinetic energy in one interaction leave the layer of anode material and continue into the block of attenuator material.