Patent ID: 7983394

Claim:
An x-ray source device, comprising: a) an evacuated tube; b) an anode coupled to the tube and including a window and a target; c) the target having a material configured to produce x-rays in response to impact of electrons; d) a cathode coupled to the tube opposing the anode and including at least one electron source configured to produce electrons accelerated towards the target in response to an electric field between the anode and the cathode, defining an electron beam; e) the target having an outer thicker region and an inner thinner region; and f) a means for expanding and narrowing the electron beam while maintaining a center of the electron beam in substantially the same location, wherein the means for expanding and narrowing the electron beam: i) narrows the electron beam to impinge mostly upon the thinner inner region of the target when a lower voltage is applied across the cathode and the anode; and ii) expands the electron beam to impinge upon the thicker outer region of the target when a higher voltage is applied across the cathode and the anode.