X-radiation (composed of X-rays) is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV. The wavelengths are shorter than those of UV rays and longer than of gamma rays?. In many languages, X-radiation is called Röntgen radiation, after Wilhelm Röntgen?, who is usually credited as its discoverer, and who had named it X-radiation to signify an unknown type of radiation. Correct spelling of X-ray(s) in the English language includes the variants x-ray(s) and X ray(s).

X-rays with photon energies above 5-10 keV (below 0.2-0.1 nm wavelength) are called hard X-rays, while those with lower energy are called soft X-rays. Due to their penetrating ability hard X-rays are widely used to image the inside of objects, e.g. in medical radiography? and airport security. As a result, the term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. Since the wavelengths of hard X-rays are similar to the size of atoms they are also useful for determining crystal structures by X-ray crystallography?. By contrast, soft X-rays are easily absorbed in air and the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer.

The distinction between X-rays and gamma rays? is not universal. One often sees the two types of radiation separated by their origin: X-rays are emitted by electrons, while gamma rays? are emitted by the atomic nucleus. An alternative method for distinguishing between X- and gamma radiation is on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10−11 m, defined as gamma rays?. These definitions usually coincide since the electromagnetic radiation emitted by X-ray tubes generally has a longer wavelength and lower photon energy than the radiation emitted by radioactive nuclei. Wikipedia, X-ray (external link)

See Also

15.08 - Dissociating Water with X-Rays - Radiolysis
Atomic Cluster X-Ray Emission
Law of Variation of Atomic Pitch by Rad-energy
Water Radiolysis

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