238U belongs to the group of fertile isotopes. The main isotopes, which have to be considered in the fuel cycle of all commercial light water reactors, are: A radiometric dating technique based on analyses of these damage trails, or tracks, left by fission fragments in certain uranium-bearing minerals and glasses is known as fission track dating. The spontaneous fission of naturally occurring isotopes of uranium (uranium-238 and uranium-235) does leave trails of damage in the crystal structure of uranium-containing minerals when the fission fragments recoil through them. For example, californium-252 (half-life 2.645 years, SF branch ratio about 3.1 percent) can be used for this purpose. Radioisotopes for which spontaneous fission is not negligible can be used as neutron sources. Spontaneous fissions release neutrons as all fissions do, so it contributes to neutron flux in a subcritical reactor. Similarly as for alpha decay, also spontaneous fission occurs due to quantum tunneling. For example, 232Th, 235U, and 238U are primordial nuclides and have left evidence of undergoing spontaneous fission in their minerals.įor heavy transuranic elements the spontaneous fission transition rate increase with the mass number and it may become the dominant decay mode at mass numbers greater than about 260. Spontaneous fission is feasible over practical observation times only for mass numbers greater than about 232. Although spontaneous fission is expected to become more probable as the mass number increases, it is still a very rare process even in uranium. This type of decay is energetically possible for a nucleus having A > 100. Spontaneous fission is also possible if we will study the nuclear binding curve. The case of decay process is called spontaneous fission and it is very rare process. In nuclear physics, nuclear fission is either a nuclear reaction or a radioactive decay process. The fission process often produces free neutrons and photons (in the form of gamma rays), and releases a large amount of energy. In general, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei).
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