"In recognition of the extraordinary services he has rendered by the discovery of the remarkable rays."
The Royal Swedish Academy of Sciences, 1901
An X-ray is a form of electromagnetic radiation with a very short wavelength, in the range 10 to 0.01 nanometers. German physicist Wilhelm Rontgen (1845-1923) was experimenting with cathode rays in 1895 when he realized that these produced another form of radiation when they hit the glass of the cathode ray tube. He called them X-rays, as "X" stands for the unknown in mathematics.
Rontgen discovered that X-rays passed through soft materials, such as paper, card, and fabric, and produced fluorescence and can be used to form images on a barium-coated photographic plate. His next experiments involved human tissue. He asked his wife to put her hand on the photographic plate and discovered that the X-rays passed through the flesh, but not through her bones, or her ring. Rontgen was awarded the first Nobel Prize for Physics in 1901.
X-rays are a form of ionizing radiation, causing ions to be produced from the atoms that they hit, which is why they produce fluorescence. It was not known until the 1950s that X-rays can damage living cells, causing cancer. Some, but not all, who worked with X-rays before this, including Rontgen, protected themselves from the radiation by using lead shields.
We now take for granted the crucial role X-rays perform in medical diagnosis, and this application developed rapidly after Rontgen's initial discovery. X-rays also proved invaluable to crystallographers who used the scatter-patterns to investigate the structure of materials. Soon after their discovery, the harmful effects of X-rays were also harnessed to develop radiographic treatments for cancer.