X-RAY
Electromagnetic radiation of very short wavelength, lying within the wavelength interval of 0.1 to 100 angstroms (between gamma rays and ultraviolet radiation). Also called "X-radiation", "Roentgen ray". X-rays penetrate various thicknesses of all solids and they act upon photographic plates in the same manner as light. Secondary X-rays are produced whenever X-rays are absorved by a substance, in the case of absorption by a gas, this results in ionization.