X-rays are a high-energy type of electromagnetic (EM) radiation. X-ray radiation has a much shorter wavelength than visible light, so X-ray photons have much higher energies than photons of light.
X-rays lie between ultraviolet “light” and gamma rays on the electromagnetic spectrum. X-ray-s have wavelengths between about 10 nanometers (10 x 10-9 meters) and 10 picometers (10 x 10-12 meters). X-ray radiation oscillates at rates between about 30 petahertz (PHz or 1015 hertz) and 30 exahertz (EHz or 1018 hertz).
X-rays are subdivided into hard X-ray-s and soft X-ray-s. The lower energy soft X-ray-s have longer wavelengths, while the higher energy hard X-ray-s have shorter wavelengths. The cutoff between the two types of X-ray-s is around a wavelength of 100 picometers or an energy level around 10 keV per photon. X-ray-s with energies between 10 keV and a few hundred keV are considered hard X-rays.
There is no sharp distinction between the highest energy X-ray-s and the lowest energy gamma rays. The distinction between X-ray-s and gamma rays is actually based on the origin of the radiation, not on the frequency or wavelength of the electromagnetic waves. Gamma rays are produced by nuclear transitions, while X-ray-s are the result of accelerating electrons.
X-rays have long been used to “see” through skin and muscle tissue to make medical “X-ray images” of bones when checking for fractures. X-rays that arrive at Earth from space are absorbed by our atmosphere before reaching the ground.