The very first X ray device was discovered accidentally by the Germanscientist Wilhelm Röntgen (1845-1923) in 1895. He found that a cathode-ray tube emitted certain invisible rays that could penetrate paper and wood and, the first person in the world to see through human flesh, even saw a perfectly clear outline of the bones in his own hand. Röntgen studied these new rays--which he called x rays--for several weeks before publishing his findings in December of 1895. For his great discovery, he was given the honorarytitle of Doctor of Medicine and awarded the 1901 Nobel Prize for physics. Adamant his discovery was free for the benefit of humankind, Röntgen refused to patent it.
X rays are waves of electromagnetic energy which behave in much the same way as light rays, but at wavelengths approximately 1000 times shorter than the wavelength of light. X rays can pass uninterrupted through low-densitysubstances such as tissue, whereas higher-density targets reflect or absorb the X rays because there is less space between the atoms for the short waves to pass through. Thus, an x ray image shows dark areas where the rays traveledcompletely through the target (such as with flesh) and light areas where therays were blocked by dense material (such as bone). Following the discoveryof x rays in 1895, this scientific wonder was seized upon by sideshow entertainers who allowed patrons to view their own skeletons and gave them picturesof their own bony hands wearing silhouetted jewelry.
The most important application of the x ray, however, was in medicine, an importance recognized almost immediately after Röntgen's findings were published. Within weeks of its first demonstration, an x ray machine was used inAmerica to diagnose bone fractures. Thomas Alva Edison invented an x-ray fluoroscope in 1896, which was used by American physiologist Walter Cannon (1871-1945) to observe the movement of barium sulfate through the digestive systemof animals and, eventually, humans. In 1913 the first x-ray tube designed specifically for medical purposes was developed by American chemist William Coolidge. X rays have since become the most reliable method for internal diagnosis.
At the same time, a new science was being founded on the principles introduced by German physicist Max von Laue (1879-1960), who theorized that crystals could be to x rays what diffraction gratings were to visible light. He conducted experiments in which the interference pattern of x rays passing through acrystal were examined; these patterns revealed a great deal about the internal structure of the crystal. William Henry Bragg and his son William LawrenceBragg took this field even farther, developing a system of mathematics that could be used to interpret the interference patterns. This method, known as x-ray crystallography, allowed scientists to study the structures of crystals with unsurpassed precision and is an important tool for scientists, particularly those striving to synthesize chemicals. By analyzing the information within a crystal's interference pattern, enough can be learned about that substance to create it artificially in a laboratory, and in large quantities. This technique was used to isolate the molecular structures of penicillin, insulin,and DNA.
Modern medical x-ray machines are grouped into two categories: "hard" or "soft" x rays. Soft x rays, which operate at a relatively low frequency, are usedto image bones and internal organs and, unless repeated excessively, cause little tissue damage. Hard x rays, very high frequencies designed to destroy molecules within specific cells thus destroying tissue, are used in radiotherapy, particularly in the treatment of cancer. The high voltage necessary to generate hard x rays is usually produced using cyclotrons or synchrotrons (variations of particle accelerators, or atom smashers).
In 1996, Amorphous silicon x-ray detectors were introduced which produce real-time, high resolution images by converting x-rays into light, the light into electrical signals which are interpreted by a computer, which produces digital data displayed as digital images, which can be enlarged to target aspecific area. Images are filmless and instantly available, formatted for electronic storage and/or transmission. First applied to mammography, this technology reduces radiation, cost of film and storage, and can be used in industrial applications. Also in 1996, researchers at NASA's Marshall Space FlightCenter developed the high resolution or high brilliance x ray which generates beams 100 times more intense than conventional x rays. These beams can be controlled and focused by reflecting them through tens of thousands of tiny curved capillaries, much as light is directed through fiberoptics.NASA is using this instrument to define the atomic structure of proteins foruse as blueprints in designing drugs. It may also initiate smaller, less expensive, and safer x-ray sources.
A familiar use for x rays is the security scanner for examining baggage at airports, while a new application for the Advanced Photon Source (APS)--the worlds largest x-ray device valued at $800 million--is in archaeology. The University of Chicago plans to utilize the machine--designed to provide biologists, chemists, physicists, and materials scientists with information into molecular structures--to analyze ancient tools. Not only harmless to these ancientartifacts, it is 10,000,000 times more accurate than other methods of determining chemical content. Meanwhile, the timber industry hopes to save millionsof dollars with new technology known as the Glass Log Technique developed at Monash University in Australia. This x-ray tube produces cross-sectionimages of logs and, combined with computerized tomography, constructs threedimensional images of the wood inside log, revealing its quality without having to saw the log open.