While experimenting with a vacuum tube (Crookes tube) to produce cathode rays, Wilhelm Conrad Roentgen, a German physicist, discovered a mysterious instance of electromangetic radiation with wavelengths of 0.01∼100 angstroms (1 angstrom [Å] equal to 1×10-8mm)between the ranges extrems of ultraviolet and gamma-ray (r-ray)ranges on November 8, 1895. He dubbed the newly discovered from of radiation the X-rays, to indicate that its nature was unknown. X-rays are invisible and are characterized by their particular types of behavior in reflection, refraction, and diffraction. They have high fluorescent, polarizing and penetrating power.

The dicovery of X-rays ushered in a new era of grealy increased precision in the diagnostic examination of the human body. Until then, medical diagnoses relied on visul inspection, percussion and auscultation. Beyond their well-known applications in the diagnosis and treatment of diseases, and sterilization of food and pharmceuticals, X-rays are also a major tool in archeological research and in industrial applications. X-ray inspection, in particular, is used in more than 70 percent of diagnosing activities throughtout the world. Roentgen received the first Nobel Prize in physics in 1901, for his discovery of X-rays.