This paper deals with the sum rules obtained from the energy moments of multipole-excitation strength functions. An explicit expression in terms of ground-state orbit-occupation probabilities is given for the total, non-energy-weighted strength of isovector excitations. For the Gamow–Teller (GT) excitation, separate sum rules are obtained for the total (p, n) and (n, p) strengths; these sum rules satisfy the Ikeda relation (S(p, n)–S(n, p) = 3(N – Z)) exactly. The GT sum rules are then used to estimate the influence of ground-state correlations on total (p, n) and (n, p) strengths in 208Pb. Sizeable strength enhancements are obtained, ranging from around 15% (in units of 3(N – Z) for longer range random-phase approximation correlations to 50% or more if short-range nuclear-matter correlations are included. An assessment is then given of the current status of the problem of missing Gamow–Teller strength in heavy nuclei. Brief concluding sections deal with the isospin splitting of isovector excitations and further development of the energy–moment sum rules.
Single and Double Charge Exchange Excitations of Spin-Isospin Mode