Antimatter Bounces off of Matter

Science fiction has often relied on matter and antimatter annihilating each other as a power source. With current technology, producing anti-matter is prohibitively expensive, and most view this as the biggest hurdle for these types of power plants. Basic physics may provide another significant hurdle, however.

Physical Review Focus reports that upon reanalyzing data from 12 years ago, an Italian team discovered that – contrary to popular belief – antimatter and matter may bounce off each other before they’re annihilated (Original paper, subscription required). The key to this discovery was the annihilation events in their data were clustered into two groups: The first group occurred when the antiprotons interacted with the helium in their apparatus, and the second set of events (up to 25% of the total number) occurred at a later time. They determined this second set occurred because the antiprotons were reflected off of the back wall of their device to be later annihilated by the helium atmosphere, instead of either annihilating the aluminum in the walls or passing through entirely. This effect is called Rutherford scattering, and at the speeds they were working with (1 – 10 keV, or 0.14 – 0.46% of c) the antiprotons are more likely to find themselves scattered by the aluminum nuclei than they are to annihilate the nuclei. At lower speeds (500 eV, or 0.10% of c), this effect may peak with 50% of the antiprotons that make it to the back wall being reflected by it.