has a barrier energy for fission of 4.2 MeV. To remove a neutron from this nuclide requires an energy expenditure of 5.0 MeV. We have to answer whether is fissionable by thermal neutrons.

Solution:             Click For PDF Version

We want to answer whether nuclide is fissionable by thermal neutrons. When a thermal neutron, kinetic energy nearly zero, is absorbed by a nuclide, the nuclide is formed in an excited state. As the binding energy of a neutron, which is alternatively defined as the energy required to remove a neutron from nuclide, is 5.0 MeV, when a thermal neutron is absorbed by a nuclide the nuclide will be in an excited state with excitation energy of 5.0 MeV.

The barrier energy for fission of nuclide is 4.2 MeV. Therefore, the energy of the nuclide formed on absorption of a thermal neutron is more than the barrier energy for fission. Therefore, nuclide

is fissionable by absorption of thermal neutrons.