Gamma rays

It seems that several readers have been searching the site for information about gamma rays. So, here’s a potted summary adapted from Wikipedia.

Gamma rays, or gamma radiation is electromagnetic energy of high frequency (very short wavelength) and so high energy. For electromagnetic radiation wavelength is inversely proportional to frequency, the proportionality constant being the speed of light. Similarly, energy and frequency are proportional in this case the relationship is governed by Planck’s constant). Gamma ray frequencies are usually above 10 exahertz (or more than 10 to the 19 Hz), and so their energies are above 100 kilo electronvolts (keV). Their wavelengths are less than 10 picometres, less than the diameter of an atom.

Gamma rays are produced naturally on Earth and elsewhere in the universe by radioactive decay of high-energy states of atomic nuclei. This form of ionising radiation is also generated when certain high-energy subatomic particles interact or through interactions of cosmic rays.

High-energy nuclear reactions are used to product gamma rays artificially for medical and research applications.  Electron-positron annihilation, neutral pion decay, fusion, and induced fission can be used to generate gamma rays.

Gamma rays are also generated by certain astronomical events in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung, inverse Compton scattering and synchrotron radiation.

The distinction between X-rays and gamma rays is arbitrary. Originally, the electromagnetic radiation emitted by X-ray tubes had a longer wavelength than the radiation emitted by radioactive nuclei (gamma rays). The older scientific literature distinguished between X-rays and gamma rays on the basis of wavelength. Today, gamma rays are now usually distinguished on the basis of their origin rather than an arbitary wavelength cut off: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus.

More on gamma rays here.


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Author: David Bradley

Award-winning, freelance science writer based in Cambridge, England.