Gamma ray spectroscopy of $^{31}$Si

$^{31}$Si was produced through the $^{18}$O ($^{18}$O, $\alpha$n) reaction at the beam energy of 24 MeV, which preferentially populates the high spin states. The $\alpha$ particles were detected in Microball and the multiple $\gamma$-ray coincidences were detected by Gammashpere. There are 11 newly observed states and 22 new discovered $\gamma$ transitions. A strong competition is seen between negative-parity {}``intruder'' states and positive-parity pure s-d states. Shell model calculations agree relatively well with both groups of states.