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 (3Ã—1016 Hz to 3Ã—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 RÃ¶ntgen radiation, after Wilhelm RÃ¶ntgen, 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 10âˆ’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