X-rays are part of the Electromagnetic spectrum. They are a penetrating form of electromagnetic radiation and consist of quantum's of energy (Photon). X-rays are commonly produced by the excitation of atomic Electrons, by firing electrons between a high potential difference towards a target (which is the principle of an x-ray machine).

The target electrons are excited, and as they de-excite x-ray photons are produced. X-rays can also be produced as a result of Bremsstrahlung or by nuclear reactions. X-rays have many uses including medical imaging and industrial quality assurance.

Whilst commonly stated (or assumed) that gamma rays are emitted by certain radioactive materials, x-rays can also be emitted if the process involves photons being produced within the electron orbit (cloud) around the nucleus (such as in the case of electron capture). An example is the radioactive substance I-125 which emits gamma rays during decay and x-rays from the post decay product(Te-125).