X-Ray
A picture produced by exposing photographic film to X-rays: used in medicine as a diagnostic aid as parts of the body, such as bones, absorb X-rays and so appear as opaque areas on the picture. Electromagnetic radiation emitted when matter is bombarded with fast electrons. X-Rays have wavelengths shorter than that of ultraviolet radiation, that is less than about 1 × 10 –8 metres. They extend to indefinitely short wavelengths, but below about 1 × 10 –11 metres they are often called gamma radiation.