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Wavelength: < 10-11m

Sources

Gamma rays are emitted from the nuclei of radioactive atoms during decay. Radioactive decay is spontaneous. This can occur when a neutron splits into an electron and a proton. K-capture also releases gamma radiation. K-capture is the capture of the inner most electron, combined with one of the nucleus' protons, to make a neutron. In both cases, the new products are of a slightly mass than the originals. This mass defect causes a release of gamma radiation (E = Dmc²).

On Earth gamma rays originate largely from cosmic radiation. One high-activity source of gamma rays is cobalt-60 (⁶⁰Co).

Detection

Bubble chambers, Geiger counters (although these are not very sensitive to gamma rays, since the latter are not very ionizing), photographic plates (silver iodide emulsion darkens when hit by gamma radiation).

Bubble chambers use a pressurized tank of H₂. High energy particles are sent through the Hydrogen, ionize it, and one can then follow the paths of the bubbles of H₂ produced using photographs.

Uses

Gamma rays can be used in many different situations. In radiotherapy they are replacing X-rays from expensive X-ray machines in the treatment of cancer. The rapidly growing cells of the diseased tissue which cause cancer are even more affected by radiation than healthy cells.

Medical instruments, bandages, and such like are sterilized (after packing, to prevent contamination and to make handling easier) by brief exposure to gamma rays. This treatment kills any microbiological organisms which may be on the instruments, thus preventing unintentional spreading of disease. No radioactivity is produced in the material irradiated by the gamma rays and thus this is perfectly safe.

A similar procedure is carried out on foods, extending their "life"-time considerably. For example, meat can be made stay fresh for fifteen days instead of three of four days.

Notes

Gamma rays are the shortest waves we can detect with current instruments. They are very intense, penetrating and dangerous to biological life, and must therefore be handled with care.

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