X-Ray
In 1895 the German physicist Wilhelm Röntgen, experimenting with a cathode ray tube, produced weak rays that caused a screen to fluoresce, or glow. In order to create a controlled environment, Röntgen placed the cathode tube in a black cardboard box, too thick for cathode rays to penetrate. Once the cathode-ray tube was turned on, however, Röntgen noticed that another screen across the room began to glow; since this second screen was too far from the tube for cathode rays to reach, especially through a layer of cardboard, Röntgen realized that he had discovered a new type of ray. Through experimentation he found that this new ray, unlike any others known at that time, was able to penetrate even the thick walls of his laboratory. Röntgen delivered a paper detailing his findings on December 28, 1895 in which he admitted that he did not know the precise nature of these new rays and chose to name them X-rays, since "x" is the mathematical symbol for the unknown.
Few discoveries have been accompanied by as much fanfare as was that of the X-ray. During the twelve months following the publication of Röntgen's findings more than a thousand books and articles on the subject were written, and that number rose to more than ten thousand before 1910. The penetrating power of X-rays to reveal bone structure was immediately recognized by the medical community as a new diagnostic tool. However, not all of the excitement was positive, since many considered the X-ray machine's ability to look through walls and doors an end to personal privacy. In fact, opera houses banned the use of X-ray binoculars in order to prevent patrons from peering beneath the actresses costumes. Nevertheless, more rational minds eventually prevailed, and Röntgen was awarded the first Nobel Prize for Physics in 1901.
X-rays are electromagnetic waves, like light waves, but with a wavelength about one thousand times smaller. Because of this very short wavelength, X-rays can easily penetrate low-density material, such as flesh, but are still reflected or absorbed by high-density material, such as bone. The picture made by an X-ray machine shows the denser materials as dark areas. The first medical use of X-rays came in 1896 when the American physiologist Walter Bradford Cannon (1871-1945) used a fluorescent screen to follow the path of bismuth subnitrate through an animal's digestive system. Soon after, physicians worldwide began using X-rays on humans, usually to examine bone fractures or to search for foreign objects, such as bullets. Thomas Edison (1847-1931) invented the X-ray fluoroscope in 1896.
Tremendous advances in X-ray technology have been achieved since the turn of the century. One of the most exciting was the development of a new science, the field of X-ray crystallography. First conceived of by the German physicist Max von Laue, this science uses X-rays to probe the molecular structure of crystal s. William Henry Bragg (1862-1942) and his son William Lawrence Bragg (1890-1971) were the first to develop a mathematical system by which the X-ray interference patterns of crystals could be examined. X-ray crystallography has become an important tool for laboratory synthesis of many chemicals and drugs. Penicillin, which was in great demand during World War II, was successfully synthesized by Dorothy Crowfoot Hodgkin. X-ray crystallography was also used to synthesize insulin and was instrumental in the discovery of the DNA molecule.
One of the most familiar X-ray machines is the baggage scanner found at airport terminals. This low-power X-ray device is placed over a conveyor belt, where it scans passengers' luggage. The machine used in this type of scanner must operate at a very specific frequency--high enough to penetrate hard-shell baggage but low enough to prevent the accidental exposure of camera film.
The most important application of X-rays, however, remains their use in medicine. By 1970, most Americans were receiving at least one X-ray exam every year from physicians and dentists. However, recent evidence has shown that X-rays are potentially harmful and can lead to the development of leukemia; many doctors thus recommend X-ray exams only when absolutely necessary. Ironically, the harmful side effects of X-rays have suggested yet another form of treatment, called radiotherapy, in which very high frequency X-rays ("hard rays") are used to destroy cancer cells. Radiotherapy is most often used in conjunction with chemotherapy.
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