Muon-catalyzed fusion is a process allowing nuclear fusion to take place at room temperature. Although it can be produced reliably with the right equipment and has been much studied, it is believed that the poor energy balance will prevent it from ever becoming a practical power source. It used to be known as cold fusion; however, this term is now avoided as it can create confusion with other scientifically unestablished forms of room-temperature fusion.
In muon-catalyzed fusion, deuterium and tritium nuclei form atoms with muons, which are essentially heavy electrons. The muons orbit very close to the nuclei, shielding the positive charge of the nuclei and allowing them to move close enough to fuse. The muons survive the fusion reactions and remain available to catalize further fusions. Andrei Sakharov and F. C. Frank predicted this effect of muon-catalized fusion on theoretical grounds before 1950.
One practical problem with the process is that muons are unstable, decaying in 2.2 microseconds. Hence there needs to be some cheap means of producing muons, and the muons must be arranged to catalyze as many reactions as possible before decaying. Another problem, recognized by J.D. Jackson in his seminal 1957 paper, is the ∼1% probability of the muon "sticking" to the alpha particle (a helium-4 nucleus) that results from the deuterium-tritium fusion, removing it from the catalysis process. Even if muons were absolutely stable, each could catalyze, on average, only about 100 fusions before sticking—about one fifth the number needed to produce more energy than is consumed to produce the muons.
In 1999, Takahiro Matsumoto reported in JP Patent No. 3073741 that an alpha-sticking probability as low as 0.03% was achieved by injecting muons into porous silicon with a deuterium and tritium terminated surface. According to the patent, a muon can catalyze more than 1000 deuterium-tritium fusions on the porous silicon surface at room temperature, and more than 1500 fusions at 500 kelvin.
References
- J.D. Jackson, "Catalysis of Nuclear Reactions between Hydrogen Isotopes by μ-Mesons," Physical Review, Vol. 106, No. 2, April 15, 1957.
- Rafelski, Johann and Steven E. Jones (1987). "Cold Nuclear Fusion". Scientific American, v. 257 #1, pp. 84–89.
See also
nuclear fusion, Antimatter catalyzed nuclear pulse propulsion
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