High spin structure and intruder configurations inP31

The nucleus $^{31}\mathrm{P}$ has been studied in the $^{24}\mathrm{Mg}$($^{16}\mathrm{O}$,2$\ensuremath{\alpha}p$) reaction with a 70-MeV $^{16}\mathrm{O}$ beam. A complex level scheme extended up to spins 17/2${}^{+}$ and 15/2${}^{\ensuremath{-}}$, 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 $\mathit{sd}\text{\ensuremath{-}}\mathit{fp}$ 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 $^{31}\mathrm{P}$.