Xrays

X-rays are a form of electromagnetic radiation with wavelengths from about 0.01 to 10 nanometers and the ability to ionize matter. They are widely used for diagnostic imaging and materials analysis.

They were discovered in 1895 by Wilhelm Conrad Röntgen during experiments with cathode rays. He produced the first X-ray photograph, of a woman’s hand, and named the radiation X because its nature was unknown at the time.

X-rays are produced when high-energy electrons strike a heavy metal target in an X-ray tube, generating Bremsstrahlung photons; a portion of emitted rays also come from characteristic radiation from inner-shell transitions. Advanced sources include synchrotrons and linear accelerators.

In matter, X-rays interact mainly through photoelectric absorption, Compton scattering, and, at higher energies, pair production. The likelihood of absorption increases with atomic number and decreases with photon energy, enabling contrast between different tissues or materials.

Applications span medical imaging (radiography, fluoroscopy, computed tomography), dental imaging, industrial radiography for nondestructive testing, security screening, and scientific methods such as X-ray diffraction in crystallography and materials science.

Safety is a central consideration because X-rays are ionizing. Risks include cancer and tissue damage, so exposure is regulated and minimized via shielding, collimation, dose limits, and dosimetry, following the ALARA principle.

Detectors used in X-ray imaging include photographic film, phosphor screens with film, digital flat-panel detectors, and computed radiography using storage phosphors. Ongoing advances aim to improve image quality while reducing patient dose.