Mean field calculation of Ne, Mg and Si nuclei at N=20 with the separable monopole interaction

A new model has been developed to study nuclei using many-body perturbation theory with a density dependent separable monopole nucleon–nucleon interaction (SMO) [Phys. Rev. C 63 (2001) 054309; P.D. Stevenson, D.Ph. Thesis, Oxford 1999; Phys. Rev. C 65 (2002) 064312]. The model is in the zeroth order an alternative to mean-field models based on more conventional effective nucleon–nucleon interactions (e.g., Skyrme, Gogny). Results on shapes and related ground state observables are reported for even–even Ne, Mg, and Si nuclei with N∼20. The model predicts the weakening of the expected N=20 shell closure in Ne isotopes and its disappearance in Mg nuclei in full agreement with experimental results.