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Giant Monopole Resonance in even-A Cd isotopes, the asymmetry term in nuclear incompressibility, and the "softness" of Sn and Cd nuclei

The isoscalar giant monopole resonance (ISGMR) in even-A Cd isotopes has been studied by inelastic $α$-scattering at 100 MeV/u and at extremely forward angles, including 0deg. The asymmetry term in the nuclear incompressibility extracted from the ISGMR in Cd isotopes is found to be $K_τ = -555 \pm 75$ MeV, confirming the value previously obtained from the Sn isotopes. ISGMR strength has been computed in relativistic RPA using NL3 and FSUGold effective interactions. Both models significantly overestimate the centroids of the ISGMR strength in the Cd isotopes. Combined with other recent theoretical effort, the question of the "softness" of the open-shell nuclei in the tin region remains open still.