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July 1960

Inside X-Ray

Author Affiliations

Santa Rosa, Calif.

From the Division of Dermatology, Department of Medicine, Stanford University School of Medicine, Palo Alto, California.

Arch Dermatol. 1960;82(1):80-89. doi:10.1001/archderm.1960.01580010086013

This exhibit attempts to show, in a simple way, what happens inside the dermatologist's x-ray machine when a treatment is given.

Thomas A. Edison, while experimenting with the filament lamp, discovered that when a piece of wire was placed in a vacuum and heated by electricity, electrons were evaporated, forming a cloud around its surface. This phenomenon, called "thermionic emission" was utilized years later by Dr. William David Coolidge, who designed the modern x-ray tube. Into a highly evacuated glass tube containing less than one-billionth of an atmosphere of pressure, he introduced a wire filament which was heated by a low-voltage circuit to supply electrons. He then introduced a separate, high-voltage circuit into the tube, with a tungsten anode (target). When the high voltage was applied to the filament, the liberated electrons were propelled at high speed to the positive anode, where their sudden deceleration produced x-rays. The flow of

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