X rays Electromagnetic waves * in the wave length range 4´ 10^-9 m to 10^-11 m, lying between ultraviolet rays and g rays. X rays are produced by X ray tube. Electrons from heated cathode, are accelerated in electrostatic field and then rapidly decelerated using targets of heavy metals. The spectrum of radiated X rays from X ray tube shows a continuous spectrum along with lines characteristic of the target used. The lines are due to electronic transition occurring in atoms that have lost inner electrons after colliding with bombarding electrons. The continuous part of the spectrum occurs when the electrons decelerate rapidly in the electrostatic field of the nuclei. This process is called Bremsstrahlung. The maximum frequency of the continuous spectrum is proportional to the kinetic energy of the electrons.

Due to their short wavelength X rays show the particle characteristic of light. In particular the Compton effect, which is particle like scattering of photons by electrons, occurs with X rays.

X rays have higher penetrating power than UV radiation. Consequently it finds wide applications. It is used for investigating the structure of crystals (see Bragg law). Another use is detection of flaws in materials. It is also an important diagnostic tool.