Resonance Structure of the Charge-Exchange Strength Function

Resumo

The resonance structure of the charge-exchange strength function S(E) is studied. Three types of isobaric resonances are considered within the self-consistent theory of finite Fermi systems and within its model approximation. These are giant Gamow-Teller, analog, and pygmy resonances (GTR, AR, and PR, respectively). The energies calculated for GTR, AR and three PRs agree well with experimental data. In heavy nuclei, the energy difference ΔE_G-A = E_GTR — E_AR tends to zero, which corresponds to restoration of Wigner’s SU(4) symmetry. The average deviation of the calculated values of ΔE_G-A from known experimental data for 33 nuclei is 0.30 MeV. The root-mean-square deviations of the calculated energies of pygmy resonances from experimental data are also moderately small, δE < 0.40 MeV. The strength function S(E) is calculated for the isotopes ⁷¹Ga, ⁹⁸Mo, ¹¹⁸Sn, and ¹²⁷I. The calculated values of the resonance energies and resonance-peak parameters are close to their experimental counterparts. A strong effect of charge-exchange resonances on neutrino-capture cross sections, including those for solar neutrinos, is demonstrated.