High spin structure and intruder configurations in 31P

The nucleus P-31 has been studied in the Mg-24(O-16,2 alpha p) reaction with a 70-MeV O-16 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 P-31.