Thermionic electron emitter and X-ray source including same

A thermionic electron emitter is proposed comprising an inner part including a heatable flat emission surface and an outer part including a surrounding surface substantially enclosing the emission surface and a heating arrangement for heating the emission surface to a temperature for thermionic electron emission. The outer part is mechanically connected to the inner part in a connection region apart from the emission surface. Furthermore, the surrounding surface is thermally isolated, e.g. by a gap, from the emission surface in an isolation region apart from the connection region. By providing a surrounding surface enclosing the emission surface which may be on a similar electrical potential as the emission surface but which can have a substantially lower temperature than the emission surface without influencing the temperature distribution within the emission surface, an improved electron emission distribution and homogeneity can be obtained.