Multi-quasi-particle states in ¹⁷³Hf

Rotational bands built on 1, 3 and 5 quasi-particle (qp) states in ¹⁷³Hf have been populated to medium and high spins through the ¹⁶⁰Gd(¹⁸O, 5n) reaction. The 1qp bands, previously identified as the 1 2^-[521], 5 2^-[512] and 7 2⁺[633] (mixed i _{13 2}) Nilsson configurations, have the first back-bend and show different alignment properties, possibly originating from deformation differences. The multi-particle states were identified from excitation energies, the properties of their associated band structures and decay patterns. The 3qp states are the previously known K^π = 19 2⁺ and 23 2^- isomeric states originating from the 7 2⁺[633] quasi-neutron coupled to 8^-, 2-quasi-proton excitations and a K^π=( 13 2⁺) state possibly containing the three lowest quasi-neutrons. A 5qp state with K^π = ( 29 2^-) was identified as the same three lowest lying quasi-neutrons coupled to the 8^-, 2-quasi-proton excitation. The low excitation energies of these two related 3-and 5-quasi-particle states implies a reduced neutron pairing gap, which can be attributed to the effect of blocking.