Observation of the Proton-Pairing Vibration inPb206

Abstract

The (${}_{}{}^3{}_{}{}^{}\mathrm{He}$, $n$) reaction was studied at an incident beam energy of 33.3 MeV for targets of ${}_{}{}^{204}{}_{}{}^{}\mathrm{Hg}$ and ${}_{}{}^{204,206,208}{}_{}{}^{}\mathrm{Pb}$. A $0^{+}$ state at 4.1 ± 0.1 MeV in ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ was excited with 70% of the cross section of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}({}_{}{}^3{}_{}{}^{}\mathrm{He},n){}_{}{}^{208}{}_{}{}^{}\mathrm{Po}\left(\mathrm{ground}\mathrm{state}\right)$ transition. This state lies at the predicted excitation energy of the proton-pairing vibration when particle-hole interactions are included.