Weak-Coupling Structure inBi207Studied with theBi209(p, t)Bi207andPb208(p, t)Pb206Reactions

The ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}(p, t){}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(p, t){}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ reactions were studied at a proton energy of 17.8 MeV in order to examine possible relationships between the nuclear structures of ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ and ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$. From a detailed comparison of the cross sections and angular distributions observed in the two reactions, it is concluded that a number of low-lying levels in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ are built upon core excitations which can be identified with the levels of ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$. The cross-section comparisons served to measure the fragmentation of the observed core strengths caused by the particle-core interaction in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$, and yielded the corresponding weak-coupling wave-function amplitudes for the low-lying ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ levels. The results show that considerable mixing occurs in ${}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ between members of a multiplet based on the $2_1^{+}$ core excitation and the single-particle proton levels, so that the $L=2\mathrm{}$ ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}(p, t){}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ cross section was not distributed according to the normal ($2J+1$) rule. The measured wave-function amplitudes are consistent with a weak-coupling structure, however, and also are consistent with ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}({}_{}{}^3{}_{}{}^{}\mathrm{He}, d){}_{}{}^{207}{}_{}{}^{}\mathrm{Bi}$ measurements of the fragmentation of the single-particle proton strengths produced by the particle-core interaction.