Neutron-capture excitation energy ($E^{\ast }=S_n(A+1,Z)+E_n^{\mathrm{CM}}$)

After neutron capture on $(A,Z)$, the compound nucleus is $(A+1,Z)$. With negligible incoming kinetic energy, conservation of energy gives $E^{\ast }=M(A,Z)+m_n-M(A+1,Z)$ in natural units. This is the neutron separation energy of the compound nucleus. At finite incident energy, add the kinetic energy in the initial centre-of-momentum frame; in a nonrelativistic heavy-target approximation it is $A/(A+1)$ times the laboratory neutron kinetic energy. Nuclear pairing can significantly change capture excitation between neighboring even- and odd-mass targets.