Gamma rays are a high-energy form of electromagnetic radiation. They can be produced in various ways including the decay of radioactive isotopes of americium and other elements, and by electronic bombardment of a metal target. Gamma rays are similar to X-rays in energy and behaviour, and have sufficient power to penetrate many solid substances and also to cause damage to living systems. They have a number of uses in medicine and science.
Gamma rays have various uses in medicine. The isotope technetium-99m is used as a radioactive tracer to image blood flow and other events in the body. The gamma knife uses a semicircular array of radioactive cobalt-60 to produce a focused beam of gamma rays that are targeted at a specific point on the body. This equipment is typically used to shrink or kill tumours of the brain. The medical imaging technology known as positron emission tomography, or PET, also makes use of gamma rays.
Gamma rays have very high penetrating power through solid objects including steel and concrete. For this reason, gamma rays can be used in a manner similar to X-rays for radiographic inspection of inanimate units such as cargo containers. The U.S. Customs currently uses gamma ray radiography for fast inspection of trucks and other large carriers crossing the border. Gamma rays are also used for non-destructive radiographic inspection of welds and related features in metal parts.
Many important celestial events produce gamma rays, such as supernovae, black holes and solar flares. By monitoring gamma rays from various areas of the universe around us, astronomers can learn important information about the structure of the universe and the various processes that go on in outer space. There are currently a number of gamma ray observation stations that are assisting scientists in understanding the behaviour of phenomena such as neutron stars in distant galaxies.
Since gamma rays are harmful to living organisms in large doses, they can be used to sterilise a wide variety of items. Gamma rays have a number of advantages over more common means of sterilisation such as heat or gas since they do not increase the temperature and degrade items and they can be applied right through most packaging. Many medical supplies are sterilised by gamma rays including surgical instruments, bandages, plastic containers and medicines.