Gamma Rays
Gamma rays or gamma-ray are forms of electromagnetic radiation (EMR) or light emissions of a specific frequency produced from sub-atomic particle interaction, such as electron-positron annihilation and radioactive decay; most are generated from nuclear reactions occurring within the interstellar medium of space. Gamma rays are generally characterized as EMR, having the highest frequency and energy, and also the shortest wavelength, within the electromagnetic radiation spectrum, i.e. high energy photons. Due to their high energy content, they are able to cause serious damage when absorbed by living cells.
Gamma rays were discovered by the French chemist and physicist Paul Ulrich Villard in 1900, while he was studying uranium. Working in the chemistry department of the Ecole Normale in rue d'Ulm, Paris with self-constructed equipment, he found that the rays were not bent by a magnetic field. For a time, it was assumed that gamma rays were particles. The fact that they could be described as rays was demonstrated by the British Physicist William Henry Bragg in 1910, when he showed that the rays ionized gas in a way similar to X-rays.
In 1914, Ernest Rutherford and Edward Andrade showed that gamma rays were a form of electromagnetic radiation by measuring their wavelengths using crystal diffraction. The measured wavelengths were similar to those of X-rays and are very short, in the range of 10-11 m to 10-14 m. It was Paul Ulrich Villard who coined the name 'gamma rays', in keeping with Rutherford's naming of 'alpha' and 'beta' radiation; the individual natures of the different rays were unknown at that time.
Gamma-ray astronomy did not develop until it was possible to get detectors above all or most of the atmosphere, using balloons or spacecraft. The first gamma-ray telescope, carried into orbit on the Explorer XI satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. Perhaps the most spectacular discovery in gamma-ray astronomy came in the late 1960s and early 1970s. Detectors on board the Vela satellite series, originally military satellites, began to record bursts of these rays, not from Earth, but from deep space.
The powerful nature of gamma rays has made them useful in the sterilization of medical equipment by killing bacteria. They are also used to kill bacteria and insects in foodstuffs, particularly meat, marshmallows, pies, eggs, and vegetables, to maintain freshness.
Due to their tissue penetrating property, gamma rays/X-rays have a wide variety of medical uses such as in CT Scans and radiation therapy (see X-ray). However, as a form of ionizing radiation they have the ability to effect molecular changes, giving them the potential to cause cancer when DNA is affected.
Despite their cancer-causing properties, gamma rays are also used to treat some types of cancer. In the procedure called gamma-knife surgery, multiple concentrated beams of gamma rays are directed on the growth in order to kill the cancerous cells. The beams are aimed from different angles to focus the radiation on the growth while minimizing damage to the surrounding tissues.
Gamma rays are also used for diagnostic purposes in nuclear medicine. Several gamma-emitting radioisotopes are used, one of which is technetium-99m. When administered to a patient, a gamma camera can be used to form an image of the radioisotope's distribution by detecting the gamma radiation emitted. Such a technique can be employed to diagnose a wide range of conditions (e.g. spread of cancer to the bones).
Gamma ray detectors are also starting to be used in Pakistan as part of the Container Security Initiative (CSI). These US$5 million machines are advertised to scan 30 containers per hour. The objective of this technique is to pre-screen merchant ship containers before they enter U.S. ports.
Gamma Ray Wikipedia
A Violent History of Time NASA - January 24, 2008
Astronomers find first ever gamma ray clock PhysOrg - November 28, 2006
Astronomers ponder weird cosmic burst News in Science - February 24, 2006
Most distant cosmic blast sighted BBC - September 12, 2005
Astronomers have witnessed the most distant cosmic explosion on record:
a gamma-ray burst that has come from the edge of the visible Universe.
Possible Source of Cosmic Rays Found Space.com - November 2004
Weak Version of Most Powerful Explosions Found Space.com - August 2004
Gamma-ray bursts are the most powerful events in the universe, temporarily
outshining several galaxies and likely signaling the birth of a black hole.
Gamma ray burst mystery solved BBC - April 2003
Thanks to a burster that was remarkably close in cosmic terms,
their true nature may have been revealed. The bursts seem
to come from exploding stars called supernovae.
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