William David Coolidge

In 1913, William David Coolidge revolutionized the field of radiology by inventing what is now referred to as the Coolidge X-ray tube. No new scientific principles or discoveries were involved, and to Coolidge's employer, the General Electric Company, the invention simply represented a new product. Nevertheless, this new product became a watershed in the field of medicine. The story of its development began in 1905 when Coolidge joined the General Electric Research Laboratory and was given the task of replacing the fragile carbon filaments in electric light bulbs with tungsten filaments. The available tungsten was difficult to work metallurgically, but Coolidge succeeded and his improved light bulb was brought to market in 1911. General Electric also manufactured X-ray tubes and Coolidge recognized that his tungsten filament together with additional modifications could significantly improve the performance of the tube. Coolidge's improved X-ray tube employed a heated tungsten filament as its source of electrons (i.e., the cathode). Since residual gas molecules in the tube were no longer necessary as the electron source, the Coolidge (or hot cathode) tube could be completely evacuated which permitted higher operating voltages. These higher voltages produced higher energy X rays which were more effective in the treatment of deep-seated tumors. In addition, the intensity of the X rays didn't show the tremendous fluctuations characteristic of earlier tubes and the operator had much greater control over the quality (i.e., energy) of the X rays. Coolidge later became Director of the laboratory and eventually Vice-President and Director of Research for General Electric. At the beginning of WW II, he was appointed to a small committee established to evaluate the military importance of research on uranium. This committee's report led to the establishment of the Manhattan District for nuclear weapons development. In 1975, with 83 patents to his credit, William David Coolidge was elected to the National Inventor's Hall of Fame, the only person to receive this honor in his lifetime.

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