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Coolidge

THE X-RAY TUBE

After receiving a bachelor's degree from MIT (1896) and a doctorate from the University of Leipzig (1899), William D. Coolidge joined General Electric's Research Laboratory in 1905. The crowning achievement of his early work (conducted with his lifelong colleague, Colin G. Fink) was the production of ductile tungsten (1910), which was then able to replace carbon as the preferred filament of incandescent light bulbs, and is still used as such today. But Coolidge's greatest moment was yet to come.

Coolidge's innovations covered a broad spectrum: he worked on magnetized steel, radar systems, and creature comfort devices like the electric blanket. In total, he was awarded 83 patents. But Coolidge has been immortalized for his invention of a vacuum tube for generating x-rays (often still called the "Coolidge tube"). This device (patent #1,203,495, granted in 1913) made the use of x-rays for medical diagnosis safe and convenient: Coolidge even invented a portable model for use during World War I. Despite subsequent advances, Coolidge's basic design has never been superseded.

X-rays are a form of energy that travels in waves much smaller than those of visible light. Coolidge's machine allowed these waves easily to be produced by the impact of high-energy electrons on a tungsten anode within a vacuum tube, and then to be directed through a substance onto a photographic plate. Denser materials within the substance being scanned absorb more x-rays, and thus produce a brighter photographic image on the plate.

It is impossible to estimate the number of lives that have been saved thanks to Coolidge's greatest achievement---to say nothing of its applications in scientific research (for example, in analyzing the structure of crystals). The "Coolidge tube" stands as a classic example of an inventive mind harnessing a phenomenon of nature and putting it to use for the good of humanity.

[Mar. 1997]

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