Inner hole states inPb207via thePb208(He3, α)Pb207reaction at 70 MeV

Abstract

The $^{208}\mathrm{Pb}(^{3}\mathrm{He}, \ensuremath{\alpha})^{207}\mathrm{Pb}$ reaction at 70 MeV incident energy was used to populate hole states up to 28 MeV excitation energy in $^{207}\mathrm{Pb}$. A split-pole spectrometer was used for particle analysis and detection. For the excitation energy range between 0 to 4.5 MeV, about eleven well resolved states are excited. These levels contain the main part of the spectroscopic strengths of the $3{p}_{\frac{1}{2}}$, $2{f}_{\frac{5}{2}}$, $3{p}_{\frac{3}{2}}$, $2{f}_{\frac{7}{2}}$, $1{i}_{\frac{13}{2}}$, and $1{h}_{\frac{9}{2}}$ neutron subshells. Three additional regions of enhanced cross sections, centered at 5.5, 8.5, and 14 MeV excitation energy in $^{207}\mathrm{Pb}$, are also observed. The 65 keV energy resolution of the present study revealed fine structure in the peak previously observed around 8.5 MeV in $^{207}\mathrm{Pb}$. About fifteen levels or groups of levels are populated between 4.5 and 10.5 MeV, and angular distributions have been extracted for each individual peak as well as for the gross structures. A distorted-wave Born-approximation analysis of the data was carried out and shows that the missing $l=3 \mathrm{and} 5$ strengths in $^{207}\mathrm{Pb}$ are located in some strong peaks at 5.13, 5.62, and 6.37 MeV. Thus the full sum rule is obtained for the neutron subshells between $N=126$ and $N=82$. The highly fragmented peak located at 8.5 MeV excitation energy is shown to arise from $1{h}_{\frac{11}{2}}$ neutron pickup. Finally, the large structure, 5 MeV wide and centered around 14 MeV, observed for the first time in this work is tentatively interpreted as arising from neutron pickup from the $1{g}_{\frac{9}{2}}$ inner shell. The ${T}_{>}$ components of the deeply-bound state are also observed between 20 to 24 MeV in $^{207}\mathrm{Pb}$ and therefore from the sum-rule analysis, centroid energies and total strengths for each inner subshell are deduced.NUCLEAR REACTION $^{208}\mathrm{Pb}(^{3}\mathrm{He}, \ensuremath{\alpha})$, $E=70$ MeV; measured $\ensuremath{\sigma}(E, \ensuremath{\theta})$. $^{207}\mathrm{Pb}$ deduced levels, ${E}_{x}$, $l$, ($J$), $\ensuremath{\pi}$, ${C}^{2}S$; inner shell spectroscopic factors; enriched target, magnetic spectrometer.