X-ray

Band of electromagnetic radiation in the wavelength range 10^-12 to 10^-8 m (between gamma rays and ultraviolet radiation; see electromagnetic waves). Applications of X-rays make use of their short wavelength (as in X-ray diffraction) or their penetrating power (as in medical X-rays of internal body tissues). X-rays are dangerous and can cause cancer.

X-rays with short wavelengths pass through most body tissues, although dense areas such as bone prevent their passage, showing up as white areas on X-ray photographs. The X-rays used in radiotherapy have very short wavelengths that penetrate tissues deeply and destroy them.

Because of their short wavelength, X-rays can be diffracted by the atoms in crystalline substances. An arrangement of a pattern of dots is formed on a photographic plate that provides information about the structure of the crystal.

X-rays were discovered by German experimental physicist Wilhelm Röntgen in 1895 and formerly called röntgen rays. They are produced when high-energy electrons from a heated filament cathode strike the surface of a target (usually made of tungsten) on the face of a massive heat-conducting anode, to which a high alternating voltage (about 100 kV) is applied.