A cathode mechanism of an electron emission source includes a crystal that includes an upper part being columnar, truncated conical, or their combined shape, and having a first surface to emit thermoelectrons, and a lower part, integrated with the upper part, having a second surface substantially parallel to the first surface, and a diameter larger than the maximum diameter of the upper part, a holding part that is a column having, in order from the holding part upper side, different inner diameters of a first diameter and a second diameter larger than the first one, and that holds the crystal in the state where the crystal first surface is projecting from the upper surface, and the crystal second surface contacts the holding part inside the column, and a retaining part that retains the crystal, at the back of the crystal lower part, not to be separated from the holding part.

Disclosed is an x-ray tube including a hybrid electron emission source, which uses, as an electron emission source, a cathode including both a field electron emission source and a thermal electron emission source. An x-ray tube includes an electron emission source emitting an electron beam, and a target part including a target material that emits an x-ray as the emitted electron beam collides with the target part, wherein the electron emission source includes a thermal electron emission source and a field electron emission source, and emits the electron beam by selectively using at least one of the thermal electron emission source and the field electron emission source.

Disclosed is an x-ray tube including a hybrid electron emission source, which uses, as an electron emission source, a cathode including both a field electron emission source and a thermal electron emission source. An x-ray tube includes an electron emission source emitting an electron beam, and a target part including a target material that emits an x-ray as the emitted electron beam collides with the target part, wherein the electron emission source includes a thermal electron emission source and a field electron emission source, and emits the electron beam by selectively using at least one of the thermal electron emission source and the field electron emission source.