Gamow-Teller strength in the 208Pb(p,n)208Bi reaction at 134.3 MeV.

Abstract

The excitation-energy distribution of transition strength to ${1}^{+}$ states was measured for the $^{208}\mathrm{Pb}$(p,n${)}^{208}$Bi reaction at 134.3 MeV for excitation energies up to 38 MeV. Structures observed in neutron time-of-flight spectra with forward-peaked (\ensuremath{\Delta}L=0) angular distributions were identified as ${1}^{+}$ states, except for the transition to the ${0}^{+}$ isobaric analog state. The ${1}^{+}$ strength in these structures was extracted by normalizing the yield above a fitted polynomial background to the Fermi transition strength localized in the isobaric analog state. The Gamow-Teller strength observed in the ${1}^{+}$ peaks is 56% of the 3(N-Z) sum rule when the strength of the ${\ensuremath{\beta}}^{+}$ transitions is assumed to be zero; 45% of 3(N-Z) is observed in the giant resonance and 10% is observed in structures below the giant resonance. Based on a multipole decomposition analysis, an upper limit on the ${1}^{+}$ strength in the apparent continuum to 38 MeV of excitation energy is estimated to be 37% of 3(N-Z). These results are compared with predictions from a shell model that includes a pairing force and a long-range Gamow-Teller force in both the parent and daughter nuclei.