Making Cold Antimatter; June 2005; Scientific American Magazine; by Graham P. Collins; 8 Page(s)
It is the nemesis of normal matter: antimatter. Like evil twins of ordinary particles, antimatter versions mirror their mundane counterparts in every way, except for having the opposite charge, and they promise violent annihilation if ever the twain should meet. Indeed, the conflagration of a single gram of antimatter particles merging with their normal matter siblings would release energy equivalent to about 40 kilotons of TNT, or enough to power nearly 5,000 households for a year.
Fortunately for our safety and unfortunately for our energy policy, antimatter is rare in the natural world. Some radioactive substances emit positrons, the antiparticles to electrons, and are used in PET (positron-emission tomography) scans. A small number of antiprotons constantly sleet down from space among cosmic rays. In addition, the giant showers of particles produced when a high-energy cosmic-ray particle strikes an atom in the atmosphere contain numerous antiparticles.