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The low-lying yrast states in the 51 Ca and 52 Sc nuclei were investigated to obtain information on the evolution of the p 1 / 2 and f 5 / 2 neutron single-particle orbitals in neutron-rich nuclei near proton number Z = 20. Level structures associated with neutron excitations into these two orbitals and with proton excitations across the Z = 20 shell gap were identified. Shell-model calculations with the recently proposed GXPF1A interaction account reasonably well for the fp -shell states. The energy separation between the νp 1 / 2 and νf 5 / 2 orbitals in the Ca isotopes appears to be overestimated by the GXPF1A Hamiltonian. ispartof: Physical Review C, Nuclear Physics vol:77 issue:1 status: published

The nucleus 31 P has been studied in the 24 Mg( 16 O,2 αp ) reaction with a 70-MeV 16 O beam. A complex level scheme extended up to spins 17/2 + and 15/2 − , on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Two shell-model calculations have been performed to describe the experimental data, one by using the code ANTOINE in a valence space restricted to the sd shell, and the other by applying the Monte Carlo shell model in a valence space including the sd - fp shells. The latter calculation indicates that intruder excitations, involving the promotion of a T = 0 proton-neutron pair to the fp shell, play a dominant role in the structure of the positive-parity high-spin states of 31 P. ispartof: Physical Review C, Nuclear Physics vol:73 issue:2 status: published

The nucleus 34 S has been studied up to relatively high spin ( I = 10 ̄ h ) and up to an excitation energy of 16.64 MeV. Data are compared with different shell model calculations where effective interactions involving two main shells, the sd and the fp , are used. For the first time in an N = Z nucleus, it is observed that the promotion of an isoscalar ( T = 0) proton-neutron pair to the fp shell becomes energetically favored at high spin ispartof: Physical Review C, Nuclear Physics vol:71 issue:1 status: published