baudrunner's space: Positronium and gamma ray lasers
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Tuesday, January 22, 2008

Positronium and gamma ray lasers

In my post Antimatter - dream or possibility? I discussed how antiprotons were produced at the Antiproton Decelerator at CERN. In theory it is possible to create new forms of matter, by replacing electrons in an atom with antiprotons, for example. Now, physicists at University of California Riverside have created a molecule made up of a pair each of electrons and positrons, the electron antiparticle. They have called it Positronium.

From Wikipedia:

"The existence of positrons was first postulated in 1928 by Paul Dirac as a consequence of the Dirac equation. In 1932, positrons were discovered by Carl D. Anderson, who gave the positron its name. The positron was the first evidence of antimatter and was discovered by passing cosmic rays through a gas chamber and a lead plate surrounded by a magnet to distinguish the particles by bending differently charged particles in different directions."
Gamma photon waves are produced during annihilation when low-energy electrons collide with low-energy positrons. Gamma radiation has some practical applications. The research at UC Riverside might make possible controlled gamma ray emission.

The researchers at Riverside fired intense bursts of positrons into thin quartz films and observed that some electrons captured the decelerating positrons to form positronium atoms. The rest collided with the positrons in the mutual annihilation process. Where the positronium atoms occupied the crystal film's internal lattices they combined with other positronium atoms to form positronium molecules. Therefore the quartz film acted as a kind of trap. The positronium molecules were briefly stable.

Traditional methods for creating antimatter have very low yields and present containment challenges. This new research might provide the way to dramatically increase antimatter yield at significantly lower costs. It also opens the door for the development of yet other novel ways to trap antimatter particles more economically and at even greater yields.

Gamma rays have the highest energy and the shortest wavelengths within the optical EM spectrum. They are 10 times more energetic than X-rays and a million times more energetic than visible light waves. This can make them very damaging to living cells. A one cm. thick lead shield reduces gamma ray intensity by 50%. It is clear that development of a gamma ray laser would be of great benefit for peaceful and military purposes. To date, this has not been accomplished. In fact, experimental results on gamma laser Em coherence have not been observed since gamma rays are emitted by a radioactive source and they lack the phase coherence emitted by the photon wavelengths of an optical laser.

Allen Mills, professor of physics at UC Riverside and assistant researcher David Cassidy next plan on using a more intense source of positrons to generate a "Bose-Einstein Condensate" of positronium atoms that are in the same quantum state. This might lead to the development of the practical gamma ray laser.

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