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Fissile Elements
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- 6.6 MeV is released on account of nuetron being absorbed or bound to U-234 nucleus.
- Thus, Binding Energy of Last Neutron is 6.6 MeV.
- Energy necessary to be supplied to induce fission is called Critical Energy for Fission.
- The binding energy of last neutron and critical energy for fission for some isotopes are listed below:
Isotope |
Critical Energy for Fission (MeV) |
Binding Energy of Last Neutron (MeV) |
Th232 |
6.5 |
5.1 |
U234 |
4.6 |
6.6 |
U236 |
5.3 |
6.4 |
U239 |
5.5 |
4.9 |
Pu240 |
4.0 |
6.4 |
- Thus when neutron is absorbed in U233 the neutron deposits its binding energy in the compound nucleus (U234 ), which is more than what is required to make U234 fission. Hence it splits spontaneously.
- Those elements which can be fissioned by zero energy neutrons are called fissile elements.
- Thus U233, U235 and Pu239 are fissile elements.
- On the other hand, Th232 and U238 need neutrons with 1.4 MeV and 0.6 MeV respectively for inducing fission. Hence these are called fissionable nuclei.
- Natural Uranium has 99.3% of U238 and 0.7% of U235.
- U235 is the only naturally occuring fissile element.
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