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William Coolidge: Vacuum Tube for X-Ray Production, 1926

Investigative Tool

In 1895, Wilhelm Conrad Roentgen accidentally observed and—through meticulous scientific investigation—defined a new type of electromagnetic radiation.

While working with a Crookes' Tube cathode ray generator, covered at the time, he noticed a glow produced in an adjacent barium platinocyanide sample. Investigation showed the fluorescence was caused by radiation originating in the Crookes' Tube, which penetrated the covering to reach the platinum compound to glow. Roentgen named his discovery "X-rays."

X-rays are the radiation given off when an electron traveling at high speed strikes a metal target. The rays rank next-to-highest in the electromagnetic spectrum; only gamma rays from nuclear decay have greater penetrating power.

The ability to penetrate tissue to varying degrees makes X-rays an important, non-invasive, investigative tool in diagnosis and treatment in both medicine and in chemical analysis. As X-rays pass through the body, they are blocked, to a greater or lesser degree, by internal organs. A photographic plate placed at the spot where the X-rays exit contains the resulting shadow picture of the internal contents.

Coolidge Photo
Photograph of Coolidge, Lantern Slide. (403K)