Röntgen's "unknown rays"
In November 1895 Wilhelm Conrad Röntgen at the University of Würzburg noticed that something from a cathode-ray tube wrapped in black paper made a fluorescent screen glow across the room. Not knowing what it was, he called it "X" radiation, like an unknown in algebra, and his image of his wife Anna Bertha's hand bones and ring astonished the world. He took out no patent and received the first Nobel Prize in Physics in 1901. The next year Henri Becquerel, investigating X-rays, discovered the radioactivity of uranium. In 1912 Max von Laue's team showed that X-rays fired into crystals produce diffraction patterns, proving they are very short-wavelength electromagnetic waves — high-energy photons.
Revealing the structure of crystals and life
In 1913 William Henry Bragg and his son Lawrence derived the law that turns diffraction angles into the arrangement of atoms in a crystal, sharing the 1915 Nobel Prize; Lawrence, at 25, remains the youngest physics laureate. That same year Henry Moseley found that each element's X-ray wavelength changes regularly with atomic number, putting the periodic table in order of atomic number. "Photo 51", taken in 1952 by Rosalind Franklin and Raymond Gosling, was crucial evidence for Watson and Crick's DNA double helix. X-ray crystallography went on to solve haemoglobin, insulin, the ribosome and coronavirus proteins. In 1962 Riccardo Giacconi's rocket experiment detected the first X-ray source beyond the solar system, founding X-ray astronomy.
Medical imaging and radiation safety
Dense tissues such as bone absorb more X-rays, which is why they are used for chest films, dental images and mammograms. In 1971 the British engineer Godfrey Hounsfield built the first CT scanner, sharing the 1979 Nobel Prize with Allan Cormack; CT combines X-ray images from many angles into cross-sections of the body. But X-rays are ionising radiation that can damage DNA, and early researchers who worked unshielded suffered burns and cancers. A chest X-ray delivers about 0.02–0.1 mSv, equal to a few days or weeks of natural background radiation, while an abdominal CT delivers around 10 mSv. In 2007 David Brenner and Eric Hall warned that soaring CT use could slightly raise long-term cancer risk. A needed scan's benefits far outweigh the risk, but avoid unnecessary repeats and always tell staff if you might be pregnant.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Are airport X-ray scanners safe?
- Baggage scanners are shielded, and body scanners mostly use non-ionising millimetre waves or extremely low doses, so the health risk is negligible.
- Is it dangerous to have X-rays often?
- Chest and dental X-rays involve very small doses, but CT scans can be hundreds of times higher. Discuss whether each scan is necessary and share previous imaging to avoid duplicates.
Sources reviewed: 2026-10-26
References
- Röntgen, W. C. (1895). Über eine neue Art von Strahlen. Sitzungsberichte der Physikalisch-Medizinischen Gesellschaft zu Würzburg, 132–141.
- Becquerel, H. (1896). Sur les radiations émises par phosphorescence. Comptes Rendus de l'Académie des Sciences, 122, 420–421.
- Friedrich, W., Knipping, P., & Laue, M. (1913). Interferenzerscheinungen bei Röntgenstrahlen. Annalen der Physik, 346(10), 971–988.
- Bragg, W. H., & Bragg, W. L. (1913). The reflection of X-rays by crystals. Proceedings of the Royal Society A, 88(605), 428–438.
- Moseley, H. G. J. (1913). The high-frequency spectra of the elements. Philosophical Magazine, 26(156), 1024–1034.
- Coolidge, W. D. (1913). A powerful Röntgen ray tube with a pure electron discharge. Physical Review, 2(6), 409–430.
- Franklin, R. E., & Gosling, R. G. (1953). Molecular configuration in sodium thymonucleate. Nature, 171(4356), 740–741.
- Giacconi, R., Gursky, H., Paolini, F. R., & Rossi, B. B. (1962). Evidence for X rays from sources outside the solar system. Physical Review Letters, 9(11), 439–443.
- Hounsfield, G. N. (1973). Computerized transverse axial scanning (tomography): Part 1. Description of system. British Journal of Radiology, 46(552), 1016–1022.
- Brenner, D. J., & Hall, E. J. (2007). Computed tomography — an increasing source of radiation exposure. New England Journal of Medicine, 357(22), 2277–2284.