Penetrating electromagnetic radiation. X-radiation is generated by slowing-down electrons or heavy charged particles. In an x-ray tube, electrons are accelerated by means of high direct voltage to bombard a metal electrode. The bremsstrahlung generated is called x-radiation.

Simplified sectional drawing of an x-ray tube (UH: heater voltage, K: cathode, A: anode, e: electrons exiting the cathode and accelerated to the anode, R: x-ray shielding, F: beam hole)