Systematics of the bimodal isoscalar giant dipole resonance

Abstract

The systematic behavior of the isoscalar giant dipole resonance (ISGDR) in $^{90}\mathrm{Zr}$, $^{116}\mathrm{Sn}$, $^{144}\mathrm{Sm}$, and $^{208}\mathrm{Pb}$ is studied with inelastic $\ensuremath{\alpha}$ scattering at ${E}_{\ensuremath{\alpha}}=386\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. Multipole-decomposition analysis is applied to extract the excitation strengths of giant resonances from the $(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}})$ differential cross sections at ${\ensuremath{\theta}}_{\mathrm{lab}}=0.64\ifmmode^\circ\else\textdegree\fi{}--13.5\ifmmode^\circ\else\textdegree\fi{}$. The bimodal structure of the ISGDR is discussed and compared with recent theoretical results from $\text{Hartree}\text{\penalty1000-\hskip0pt}\text{Fock}+\text{random}\text{\penalty1000-\hskip0pt}\text{phase}\text{\penalty1000-\hskip0pt}\text{approximation}$ calculations.