Band structures and proton-neutron interactions in 174Ta

Six rotational bands in the odd-odd nucleus Ta-174 have been populated with the Gd-160(F-19,5n) reaction. High-spin states were identified using the NORDBALL array. Both signatures of the doubly decoupled pi 1/2(-)[541] circle times nu 1/2(-)[521] band and semi-decoupled pi 1/2(-)[541] circle times nu 7/2(+)[633] band are observed, in addition to the high-K couplings of the pi 9/2(-)[514] circle times nu 7/2(+)[633], pi 9/2(-)[514] circle times nu 5/2(-)[512], pi 7/2(+)[404] circle times nu 7/2(+)[633], and pi 5/2(+)[402] circle times nu 5/2(-)[512] configurations. The signature splitting of the pi 1/2(-)[541] circle times nu 7/2(+)[633] band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. It is shown empirically that this interaction, together with deformation changes, can account for the increased crossing frequency associated with the alignment of i(13/2) neutrons in the pi 1/2(-)[541] bands of odd-Z nuclei. (C) 1998 Elsevier Science B.V.