X-ray tube(10點)

the fast-moving electrons hit on the metal and decelarate on the metal. the energy on the fast-moving electrons transferred to the electrons on the heavy metal. the electrons on the metal will excite to a higher energy state and jump back down to its ground state via a series of transitions. X-ray will be emitted when they come back to their ground state. as these heavy metal has closely packed structure, electrons can only strick on that. even gramma ray will decline its half radation after passing through such heavy metal.