Proton stripping to outer subshells and the damping of single-particle states:Sn116,Sm144, and(α208,t) reactions at 80 MeV

The stripping reaction (α,t) at 80 MeV incident energy has been used to study the proton-particle response function on ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{144}{}_{}{}^{}\mathrm{Sm}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ target nuclei up to 22 MeV excitation energy. Rather complete spectroscopic information has been obtained on the low-lying proton states (0–3 MeV) through angular distribution measurements and standard distorted wave Born approximation analysis. Strong transitions to high-lying proton states located between 5 and 12 MeV excitation energy in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Eu}$ and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ are observed whereas the spectrum from the ${}_{}{}^{116}{}_{}{}^{}(\mathit{\alpha }$,t) reaction displays only broad, weak enhancement of cross sections at high excitation. These transitions appear as broad bumps superimposed on a continuous background for which a qualitative analysis within the framework of the breakup model has been attempted. The excitation energies, angular distributions, and strengths of these high-lying transitions suggest that they arise from proton stripping to high-spin outer subshells, e.g., 1h(9/2) and 1i(13/2) in ${}_{}{}^{145}{}_{}{}^{}\mathrm{Eu}$, and 1i(11/2) and 1j(15/2) in ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$. A distorted-wave Born approximation analysis using resonant form factors for the states located above the proton threshold has been carried out. The deduced proton strength distributions are compared with the predictions from the quasiparticle-phonon and single-particle vibration coupling nuclear models. Around 12–14 MeV excitation energy, narrow peaks corresponding to the population of the isobaric analog states in ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sb}$ and ${}_{}{}^{145}{}_{}{}^{}\mathrm{Eu}$ are also observed. Our results are compared to the known spectroscopic properties of the corresponding parent states in ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{145}{}_{}{}^{}\mathrm{Sm}$.