Calculate the excitation energy of the compound nuclei produced when { }^{235} U \text { and }{ }^{238} U absorb thermal neutrons.
Strategy The two reactions are
\begin{aligned}&n+{ }^{235} U \rightarrow{ }^{236} U ^{*} \\&n+{ }^{238} U \rightarrow{ }^{239} U ^{*}\end{aligned}As we did in Example 13.4, we find the excitation energy from the atomic masses using Equation (13.11). A thermal neutron has a negligible kinetic energy (about 0.03 eV).
E\left( CN ^{*}\right)=M_{x} c^{2}+M_{X} c^{2}-M_{C N} c^{2} (13.11)