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

TL;DR

This study investigates the direct proton decay of the isoscalar giant dipole resonance in lead-208 using alpha scattering and proton detection, providing experimental data that tests theoretical CRPA predictions.

Contribution

First experimental measurement of direct proton decay of ISGDR in 208Pb with comparison to CRPA calculations.

Findings

Proton decay partial branching ratios were determined.

Discrepancies observed between excitation spectra and decay measurements.

Results support and challenge existing theoretical models.

Abstract

The excitation and subsequent proton decay of the isoscalar giant dipole resonance (ISGDR) in $^{208}$Pb have been investigated via the $^{208}$Pb($\alpha, \alpha^{\prime}p)^{207}$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($\alpha,\alpha^{\prime}$) 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.