Splitting of ISGMR strength in the light-mass nucleus ${}^{24}$Mg due to ground-state deformation

The isoscalar giant monopole resonance (ISGMR) strength distribution in ${}^{24}$Mg has been determined from background-free inelastic scattering of 386-MeV $\alpha$ particles at extreme forward angles, including 0${}^{\circ }$. The ISGMR strength distribution has been observed for the first time to have a two-peak structure in a light-mass nucleus. This splitting of ISGMR strength is explained well by microscopic theory in terms of the prolate deformation of the ground state of ${}^{24}$Mg.