-
Fusion is the process of joining two atomic nuclei with the same charge to form a heavier nucleus---for example, two hydrogen atoms can combine to form one helium atom. This is accompanied by a release of energy. Stars, for example, are powered by nuclear fusion. The fusion occurring in the sun gives Earth the heat and light we need to exist.
Fusion can also be produced under artificial conditions. Fusion was first observed by Mark Oliphant in 1932, resulting in the creation of the hydrogen bomb. The thermonuclear reaction generated by the first full-scale test of a fusion bomb, the Teller-Ulam configuration, had a yield of 10.4 megatons, making it more than 450 times more powerful than the atomic (fission) bomb dropped on Nagasaki during World War II. - Though the potential energy yield from a fusion reaction is quite large, fusion reactors operate at very high temperatures and pressures, and at present don't do much more than break even. They are fairly safe but expensive, and as of 2009 questions remain as to whether a nuclear fusion plant could be economically viable.
- Cold fusion refers to a group of experiments conducted by Martin Fleischmann and Stanley Pons in 1989. They published an experiment involving electrolysis of heavy water (water containing a high proportion of the isotope deuterium) and a palladium electrode; this setup was reported to produce excess heat, in theory the product of nuclear fusion taking place. If this were the case, this "cold" fusion would provide a cheap source of energy. Other methods of cold fusion, such as Muon-catalyzed fusion, do exist, but have not been reported to produce net energy.
- In theory, a palladium cathode is inserted into heavy water within a calorimeter, and electricity is applied. Because of the properties of deuterium and the ability of palladium to absorb hydrogen, theoretically the deuterium will accumulate within the cathode and nuclear fusion will take place, with the resulting energy release measured by the calorimeter. Fleishmann and Pons claimed that after several weeks, the temperature of the deuterium rose from 30 degrees Celsius to 50 degrees Celsius without any change in the input of power.
- In practice, the results could not be replicated. A later review of Fleishmann and Pons' results suggested that claims of nuclear fusion had been made incorrectly. Although a few proponents still suggest cold fusion will one day provide a viable energy source for the world, in general it is considered a dead subject by physicists.
