Within a year of their discovery by Roentgen in 1895, X-rays were applied to medical diagnosis and therapy. It took another century before they started to be used for industrial processing.
X-rays refers to electromagnetic radiation (no rest mass, no charge) of high energies travelling at the speed of light and ionizing matter essentially via indirect ionization. Like gamma radiation, X-rays arehigh-energy photons, but gamma rays are emitted at defined energies during the radioactive decay of elements such as cobalt-60. X-rays are emitted as a spectrum of energies in a continuous way by the interaction of accelerated electrons with atoms’ electrons and nuclei.