x-rays

roentgen rays

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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.

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electromagnetic waves of short wavelengths (approximately 0.01 to 10 nm) or corresponding quanta (wave mechanics), produced when electrons moving at high velocity impinge on various substances, especially heavy metals. They are commonly generated by passing a current of high voltage (10,000 volts or more) through a Coolidge tube. They can penetrate most substances to some extent, some more readily than others, and transform a photographic plate, which enables their use for radiography. They can also cause certain substances to fluoresce, making fluoroscopy possible. Because of the high energy of their quanta, they strongly ionize tissue through which they pass by means of the photoelectrons (both primary and secondary) that they liberate. This makes them useful in treatment of various pathological conditions (see radiotherapy). Formerly called roentgen r's.