²³⁵U is readily made fissionable by a thermal neutron but ²³⁸U is not because: A) the neutron has a smaller binding energy in ²³⁶U B) the neutron has a smaller excitation energy in ²³⁶U C) the potential barrier for the fragments is less in ²³⁹U D) the neutron binding energy is greater than the barrier height for²³⁶U and less than the barrier height for ²³⁹U E) the neutron binding energy is less than the barrier height for ²³⁶U and greater than the barrier height for ²³⁹U

Question

Quizplus · Accepted Answer

In order for a nucleus to undergo fission with a thermal neutron, the neutron must be captured by the nucleus and create an excited state that is unstable and can undergo fission. The nucleus that is readily made fissionable by a thermal neutron is ²³⁵U, which means that a thermal neutron has a binding energy that is greater than the barrier height and can cause the nucleus to undergo fission. On the other hand, ²³⁸U is not readily fissionable with a thermal neutron because the neutron binding energy is greater than the barrier height for ²³⁶U and less than the barrier height for ²³⁹U. This means that the neutron cannot create an excited state that can undergo fission and the nucleus will not undergo fission. Therefore, choice D is the best choice because the neutron binding energy is greater than the barrier height for ²³⁶U and less than the barrier height for ²³⁹U.

235U Is Readily Made Fissionable by a Thermal Neutron but 238U

²³⁵U Is Readily Made Fissionable by a Thermal Neutron but ²³⁸U