Thermal fission may also occur in some other transuranic elements whose nuclei contain odd numbers of neutrons. However, low-energy (slow, or thermal) neutrons are able to cause fission only in those isotopes of uranium and plutonium whose nuclei contain odd numbers of neutrons ( e.g. Nuclear fissionįission may take place in any of the heavy nuclei after capture of a neutron. Whether fission takes place, and indeed whether capture occurs at all, depends on the velocity of the passing neutron and on the particular heavy nucleus involved. But in certain cases the initial capture is rapidly followed by the fission of the new nucleus. In this example, U-239 becomes Np-239 after emission of a beta particle (electron). The new nucleus may decay into a different nuclide. A simple example is U-238 + n => U-239, which represents formation of the nucleus U-239. Capture involves the addition of the neutron to the uranium nucleus to form a new compound nucleus. When a neutron passes near to a heavy nucleus, for example uranium-235 (U-235), the neutron may be captured by the nucleus and this may or may not be followed by fission. For more information on how a nuclear power plant works, see information page Nuclear Power Reactors. Neutrons in motion are the starting point for everything that happens in a nuclear reactor.
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