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Spontaneous fission
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  • All heavy nuclei are unstable to spontaneous fission into two lighter fragments.  However, for all but extremely heavy nuclei, this process is obstructed by a potential barrier, the activation energy, and hence the process is not significant except for some transuranic isotopes of very large mass number.
  • Nuclear surface tension tries to maintain a spherical shape, but the coulomb energy decreases as the nucleus becomes deformed and hence acts in the opposite "direction".
  • Two fragments form which break apart and repel each other in opposite directions due to the conservation of momentum.  Due to there being an excess of one neutron per fragment, the self-sustaining process of a chain reaction occurs (see next page).
  • Even though fission only occurs in about 3% of the decays, the neutron production rate of 2.31012 n sec-1 g-1 of 252Cf makes it a prolific, compact source.

See also:
Chain reaction
Activation energy


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