baudrunner's space: antimatter

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.

The current production of antimatter is entirely experimental in scope, and is accomplished only for the purpose of scientific investigation and to support or assist in refining particle theory. If antimatter production were commercially viable then we would have the answer to all of our energy concerns because one gram of antimatter could drive one hundred thousand cars for about a year. But it is not commercially viable at the present time. All the antimatter production done at CERN over the last ten years amounts to about a billionth of a gram in a program that has cost a few hundred million euros. That would make that one gram of antimatter cost about seven hundred million billion dollars, or $700,000,000,000,000,000.00 at today's prices. That doesn't make the price of gasoline seem so outrageous now, come to think of it.

A "self-contained antiproton factory", the Antiproton Decelerator (or AD), is operational at CERN. It is designed to produce, collect, cool, decelerate and eventually extract antiprotons.

Targets, usually copper or iridium, are bombarded with a high energy stream of protons. This releases a huge amount of energy compacted in a small space in which matter-antimatter particles are spontaneously created. Antiproton-proton pairs are formed in about one in a million collisions, but with about 10 trillion protons hitting the target every minute a good 10 million antiprotons are directed into the AD at a time. Through a process of magnetic confinement and super cooling the antiproton package is coerced into a tight bunch travelling at about 10% of light speed.

The current state of the art in antiproton experimentation is in the creation of antihydrogen, which consists of combining antiprotons with positrons from a radioactive source, and in creating other exotic atoms by replacing the electrons of atoms with antiprotons.

I see the researchers at CERN moving forward in leaps and bounds in advancing the science of antimatter production. Perhaps some day we will be driving cars powered by this exotic fuel source, who knows?

Before that happens, we would certainly be powering our spacecraft with antimatter. With the highest energy density of any material currently found on earth, a mere 100 milligrams of the stuff provides the propulsive energy of the space shuttle. A process called antiproton catalyzed microfission (ACMF) developed at Penn state University allows 100% of the energy from a fission reaction to be used for propulsion. A team there has already developed a spacecraft utilizing this technology which would require the nominal amount of 140 nanograms of antimatter to send a manned spacecraft to Mars in about thirty days. Even more advanced spacecraft have been envisioned in which antimatter and fissionable material are used to spark a microfusion reaction. Requiring somewhat more antimatter than the ACMF engine but less fissionable material, the effective specific impulse, a measure of rocket or jet engine efficiency, is increased by a factor of two over ACMF.

The chief obstacle to actually building and using these engines is in the storage and transportation of antimatter. Thus far, the Antimatter Group at Penn State have constructed and proved a portable antimatter storage (Penning) trap which can store 100 billion antiprotons for one week. NASA has taken an interest in this project and is using the Penn State results to develop a Penning trap that can store ten trillion antiprotons, enough to potentially support hundreds of reactions over a two minute time-frame. A good explanation of the technologies I have described can be found at The Encyclopedia of Astrobiology Astronomy and Spaceflight.

The first practical application of antimatter that will be realized is in the field of medicine. NASA is developing its Penning trap with the idea of harnessing the antiproton for radiotherapy of tumors. Additionally, a by-product of the Penning trap is the generation of the Oxygen isotope O-15, which is used in Positron Emission Tomography of the human brain. Only a few research hospitals around the world have the ability to create O-15, and the Penning trap would make possible the delivery of this valuable element to any hospital.