- microwaves and infrared bands whose waves are longer than those of visible light (between radio and the visible)
- and UV, EUV, X-rays and g-rays (gamma rays) with shorter wavelengths.
Medical X-raysX-rays are capable of penetrating some thickness of matter. Medical x-rays are produced by letting a stream of fast electrons come to a sudden stop at a metal plate; it is believed that X-rays emitted by the Sun or stars also come from fast electrons.
The images produced by X-rays are due to the different absorption rates of different tissues. Calcium in bones absorbs X-rays the most, so bones look white on a film recording of the X-ray image , called a radiograph. Fat and other soft tissues absorb less, and look gray. Air absorbs the least, so lungs look black on a radiograph.
Wilhelm Conrad Röntgen - First X-rayOn 8 Nov, 1895, Wilhelm Conrad Röntgen (accidentally) discovered an image cast from his cathode ray generator, projected far beyond the possible range of the cathode rays (now known as an electron beam). Further investigation showed that the rays were generated at the point of contact of the cathode ray beam on the interior of the vacuum tube, that they were not deflected by magnetic fields, and they penetrated many kinds of matter.
A week after his discovery, Rontgen took an X-ray photograph of his wife's hand which clearly revealed her wedding ring and her bones. The photograph electrified the general public and aroused great scientific interest in the new form of radiation. Röntgen named the new form of radiation X-radiation (X standing for "Unknown"). Hence the term X-rays (also referred as Röntgen rays, though this term is unusual outside of Germany).
William Coolidge & X-Ray TubeWilliam Coolidge invented the X-ray tube popularly called the Coolidge tube. His invention revolutionized the generation of X-rays and is the model upon which all X-ray tubes for medical applications are based.
Other inventions of Coolidge: invention of ductile tungsten
A breakthrough in tungsten applications was made by W. D. Coolidge in 1903. Coolidge succeeded in preparing a ductile tungsten wire by doping tungsten oxide before reduction. The resulting metal powder was pressed, sintered and forged to thin rods. Very thin wire was then drawn from these rods. This was the beginning of tungsten powder metallurgy, which was instrumental in the rapid development of the lamp industry - International Tungsten Industry Association (ITIA)