"Bi-modal'' Isoscalar Giant Dipole Strength in ${}^{58}$Ni

Abstract

The strength distribution of the isoscalar giant dipole resonance (ISGDR) in ${}^{58}$Ni has been obtained over the energy range 10.5--49.5 MeV via extreme forward angle scattering (including 0${}^{\circ }$) of 386 MeV $\hat{I}\pm$ particles. We observe a ``bi-modal'' $E1$ strength distribution for the first time in an A $<$ 90 nucleus. The observed ISGDR strength distribution is in good agreement with the predictions of a recent QRPA calculation.

14 pages, including 5 figures