MEANING OF X-RAYS
X-rays pl. n. electromagnetic radiation of extremely short wavelength (beyond the ultraviolet), which pass through matter to varying degrees depending on its density. X-rays are produced when high-energy beams of electrons strike matter. They are physically indistinguishable from gamma rays, produced during radioactive decay. Both are used in diagnostic *radiology (see RADIOGRAPHY, NUCLEAR MEDICINE) and in *radiotherapy. Great care is needed to avoid unnecessary exposure, because the radiation is harmful to all living things (see IONIZATION, RADIATION SICKNESS). Heavy elements, such as lead and barium, tend to stop X-rays and can be used to shield people from unwanted exposure to ionizing radiation.