Direct proton decay of the isoscalar giant dipole resonance in 208Pb

Abstract

The excitation and subsequent proton decay of the isoscalar giant dipole resonance (ISGDR) in ${}^{208}$Pb have been investigated via the ${}^{208}$Pb($\hat{I}\pm ,\hat{I}{\pm }^{\prime }p{)}^{207}$Tl reaction at 400 MeV. Excitation of the ISGDR has been identified by the difference-of-spectra method. The enhancement of the ISGDR strength at high excitation energies observed in the multipole-decomposition-analysis of the singles ${}^{208}$Pb($\hat{I}\pm ,\hat{I}{\pm }^{\prime }$) spectra is not present in the excitation energy spectrum obtained in coincidence measurement. The partial branching ratios for direct proton decay of ISGDR to low-lying states of ${}^{207}$Tl have been determined and the results are compared with predictions of continuum random-phase-approximation (CRPA) calculations.

12 pages, 4 figures; accepted for publication in Physics Letters B