a band of electromagnetic radiation with wavelengths between gamma rays and ultraviolet radiation (c. .005 to c. 5 nanometres), capable of penetrating opaque or solid substances, ionizing gases and body tissues through which they pass or, by extended exposure, destroying tissue, and affecting photographic plates and fluorescent screens, used in medicine for study, diagnosis, and treatment of certain organic disorders, esp. of internal structures of the body; X-ray.