Negative-parity intruder states of the neutron-rich N = 20 , Z = 14-16 isotones: a 1ℏ shell model descriptionM. Bouhelal, F. Haas, E. Caurier, F. Nowacki and A. BouldjedriEur. Phys. J. A, 42 3 (2009) 529-533DOI: https://doi.org/10.1140/epja/i2009-10782-9