Excitation of the Isovector Giant Dipole Resonance by Inelastic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>α</mml:mi></mml:math>Scattering: An Experimental Approach

Abstract

The excitation of the isovector giant dipole resonance by inelastic scattering of 120-MeV $\ensuremath{\alpha}$ particles has been studied with the $^{208}\mathrm{Pb}(\ensuremath{\alpha}, {\ensuremath{\alpha}}^{\ensuremath{'}}, \ensuremath{\gamma})^{208}\mathrm{Pb}$ reaction for $0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}{\ensuremath{\theta}}_{{\ensuremath{\alpha}}^{\ensuremath{'}}}\ensuremath{\le}3\ifmmode^\circ\else\textdegree\fi{}$. The $\ensuremath{\gamma}$-decay branching ratio to the ground state, extracted from the coincidence data, indicates that not more than (12\ifmmode\pm\else\textpm\fi{}4)% of the observed singles resonance cross section around 13.6 MeV in $^{208}\mathrm{Pb}$ can be due to isovector dipole excitation.