X-ray tube

When an energetic electron comes near to a (tungsten) target atom, it is subjected to strong replusive force from the cloud of orbital electrons. This leads to rapid decceleration of the electron. According to classical electromagnetic theory, the decceleration of a charged particle will release its energy in the form of electromagentic waves (photon). Hence, in the case of high energy electron bombarding a tungsten trage, the released electromagnetic waves are within the x-ray range.

However, the process is not as simple as that. There are thermal vibrational motions of the tungsten atoms. What makes the picture more complicated is that not all tungsten atoms in the target are vibrating with the same energy. Some atoms vibrate faster (i.e. possess more thermal energy) than others. Thus, when a beam of electrons incident onto these vibrating atoms, not all electrons lose the same amount of energy as x-rays. Some electrons lose more energy and some less energy. As such, the energy of x-ray produced follows a dstribution.

The strong repulsive force exterted between the bombarding electrons and tungsten atoms also causes the target atom to gain in vibrational energy, which is manifested as heat in the target.