Nuclear Structure Features of Gamow-Teller Excitations

It is widely accepted that nuclear Gamow-Teller transitions are quenched; shell-model calculations also showed a clear anticorrelation between the Gamow-Teller strength and the transition rate of the collective quadrupole excitation from the ground state. We discuss the physics beyond this observation. It is based on the existence of spin-orbit coupling that is responsible for the non-zero probabilities of Gamow-Teller transitions in self-conjugate nuclei (N = Z). The shell-model calculations in the f p-space demonstrate the effects of the gradual artificial removal of the spin-orbit coupling that influences Gamow-Teller and quadrupole modes in opposite way. The realistic spin-orbit splitting moves the cumulative Gamow-Teller strength up and leads to stronger fragmentation; both trends are discussed in terms of simple symmetry arguments. Along with this process, the Gamow-Teller operator excites, in addition to the main line of L = 0 states, states with L = 2 which should be added, with the interference terms, to account for the total strength.