Enhancement of M1 Transition Rates at High Spin in ⁹⁰Mo

High spin states in ⁹⁰Mo have been populated through the ⁵⁹Co (³⁵Cl,2p2n) ⁹⁰Mo reaction at beam energy of 116 MeV. Level lifetimes of the positive-parity decay sequence are measured by using the Doppler shift attenuation method. It is observed that the M1 transition strengths show a substantial enhancement at high spin. This behaviour may be related to occupation of high Ω orbitals by a pair of g_9/2 protons. A deformed shape with oblate is suggested above the 13⁺ state.