<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> In nuclear physics, nuclear fusion is a reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the products and reactants is manifested as the release of large amounts of energy . This difference in mass arises due to the difference in atomic "binding energy" between the atomic nuclei before and after the reaction . Fusion is the process that powers active or "main sequence" stars, or other high magnitude stars . </P> <P> The fusion process that produces a nucleus lighter than iron - 56 or nickel - 62 will generally yield a net energy release . These elements have the smallest mass per nucleon and the largest binding energy per nucleon, respectively . Fusion of light elements toward these releases energy (an exothermic process), while a fusion producing nuclei heavier than these elements, will result in energy retained by the resulting nucleons, and the resulting reaction is endothermic . The opposite is true for the reverse process, nuclear fission . This means that the lighter elements, such as hydrogen and helium, are in general more fusible; while the heavier elements, such as uranium and plutonium, are more fissionable . The extreme astrophysical event of a supernova can produce enough energy to fuse nuclei into elements heavier than iron . </P>

What happens in the sun fission or fusion