X-ray tube with a low-temperature emitter

An x-ray tube comprising:

• an anode at an anode potential, said anode having an incident surface with a surface normal;
• an electron emitter which emits an electron beam which strikes said incident surface of said anode in a focal spot, thereby producing an x-ray beam emanating from said focal spot and ions, said x-ray beam having a central ray, said electron emitter having an electron-emitting surface and said electron emitter comprising, at least in a region of said electron-emitting surface, electron-emitting material having a lower electron affinity than tungsten;
• said electron emitter being disposed in a region subject to permeation by said ions:
• means for protecting said region of said electron-emitting surface from being struck by said ions consisting of a diaphragm at anode potential disposed between said electron emitter and said anode having an aperture through which said electron beam passes, said diaphragm being disposed perpendicularly relative to said electron beam;
• and
• said electron emitter being disposed relative to said anode so that said electron beam is incident on said focal spot at a first angle relative to said surface normal which is greater than 45.degree., and so that said central ray of said x-ray beam is disposed at a second angle relative to said surface normal which is substantially equal to said first angle.