On November 8, 1895, Rontgen discovered the phenomenon of "running light" on the dry film. He was determined to figure it out. After a series of experimental studies, Roentgen realized that this might be a kind of radiation that has never been discovered, and it has a particularly strong penetrating power. Roentgen used X-Ray to take a picture of his wife's hand, showing the skeleton structure of the hand.
In the same year, Roentgen submitted the first research newsletter "A New Ray - Preliminary Report" to the Wuerzburg Institute of Physics and Medicine. In his communication, Roentgen called it X-ray (the unknown symbol X often used in mathematics) because he could not determine the nature of this new ray.
X-ray make the invisible to visible, the discovery by Roentgen immediately evoked a strong response in the scientific community, and almost all European laboratories immediately used X-ray tubes to test and photograph.
In order to commemorate Roentgen's contribution to physics, later generations also called X-rays as roentgen rays, and the name of Roentgen as the unit of exposure for X-rays. Roentgen won the Nobel Prize in Physics for his discovery, but he never tried to apply a patent for x-ray.
Before 1912, X-rays were barely used outside the medical and dental fields, although some X-rays photo of metal were produced. The reason why X-rays are not used in industry is that the casting industry generally requires an x-ray source with super penetrating power, which requires the tube to operate at extremely high voltages, and the X-ray source designed at that time cannot works at that high voltage. However, things changed when the high vacuum X-ray tube designed by Coolidge in 1913, became available. The high vacuum tube is a powerful and reliable X-ray source with an operating energy of up to 100,000 volts.
In 1922, with the advent of 200,000 volt X-ray tubes, X-ray photographs of thick steel parts were easily produced, and the industrial application of x-rays took another step forward.
Today, X-ray technology is widely used in medical, material analysis and airport security scanners.