Radiation generating tube, and radiation generating apparatus and radiation imaging system using the same

An X-ray generating tube, comprising:

• an insulating tube having a tube body extending along a longitudinal direction and a pair of ends;
• a cathode secured to one of the pair of ends and including an electron emitting source, the cathode having a peripheral portion joined to an end face of the one of the pair of ends;
• and
• an anode secured to the other of the pair of ends and including a target, the anode having a peripheral portion joined to an end face of the other of the pair of ends,
• wherein at least any one of the cathode and the anode includes a tubular extending portion extending along the longitudinal direction,
• wherein the tubular extending portion has a higher coefficient of thermal expansion than the insulating tube,
• wherein the tubular extending portion is secured to the insulating tube via a tubular joint portion, and
• wherein the insulating tube has a thinner tube wall region having a thinner tube wall than the tubular joint portion of the insulating tube, said thinner tube wall region being distant from the tubular joint portion along the longitudinal direction.