gammarays

Gamma rays are a form of electromagnetic radiation with the highest energies and shortest wavelengths in the electromagnetic spectrum. They are typically produced by radioactive decay, nuclear transitions, and certain high-energy processes in space. Photon energies commonly exceed 100 keV (0.1 MeV) and wavelengths are shorter than about 0.01 nanometers. Because of their penetrating power, gamma rays require dense shielding to reduce exposure.

Natural sources include gamma rays from radioactive decay in rocks and the atmosphere, as well as cosmic gamma rays from astronomical sources such as supernova remnants and active galactic nuclei. Man-made sources include medical isotopes (for example technetium-99m, iodine-131) and industrial sources (such as cobalt-60, iridium-192).

Gamma rays interact with matter mainly through the photoelectric effect, Compton scattering, and, at higher energies, pair production. These interactions enable imaging and spectroscopy but also drive biological damage as they ionize atoms along their path. Shielding typically employs dense materials such as lead or concrete, with thickness chosen to meet safety requirements.

Detection and measurement are performed with scintillation detectors (for example, sodium iodide) and semiconductor detectors such as high-purity germanium for gamma spectroscopy. In medicine, gamma rays are used for imaging (SPECT, and, with PET, annihilation photons at 511 keV) and for radiotherapy. Industrially, gamma sources enable nondestructive testing and sterilization.

Safety and regulation emphasize minimized exposure, monitoring, and proper licensing of sealed sources. Common units include the gray for absorbed dose and the sievert for effective dose.