Abstract: In an X-ray source for radiographic apparatus of the type known as computerized axial tomography (CAT) scanners it has been suggested to scan a beam of electrons across a target/anode to correspondingly scan a beam of X-rays relative to a patient. The target is inclined to the electrons mean direction to direct the X-rays in another direction. If a ribbon shaped beam of electrons is used then the shape and orientation of the region of contact, of the electrons, changes. It is proposed to preshape and preorientate the electron beam to retain the desired region of contact, and hence the desired X-ray distribution, during the scanning.