Gamow-Teller strength function forZr90: Effects of spin and isospin exchange forces, and ground-state correlations

Abstract

Shell-model calculations of the Gamow-Teller strength function for $^{90}\mathrm{Zr}$ have been performed utilizing a realistic finite-range two-body interaction in a model space consisting of the $2p$ and $1g$ shells. The effects of admixtures of two-particle two-hole excitations in $^{90}\mathrm{Nb}$, mostly due to the spin and isospin exchange components of the nucleon-nucleon force, are discussed. Ground state correlations in $^{90}\mathrm{Zr}$ are also added via seniority-zero two-proton excitations from the $2p$ shell into the $1{g}_{\frac{9}{2}}$ shell. With the correlations the Gamow-Teller strength function is in good agreement with the experimental results and accounts for essentially all of the observed dispersion of strength. The inclusion of these correlations does not, however, produce either a displacement of Gamow-Teller strength to higher excitation energies, or a significant change in the total strength. Thus, they cannot account for the observed Gamow-Teller quenching. The quenching factor derived by a comparison of our calculated results with experiment is 0.52.NUCLEAR STRUCTURE $^{90}\mathrm{Zr}$ calculated Gamow-Teller strength function. Analyzed contributions from two-particle two-hole admixtures in the $1g$-shell and parent ground-state correlations.