Near-yrast, medium-spin structure of the Tc109 nucleus

Excited levels in the Tc109 nucleus, populated in the spontaneous fission of Cm248, have been studied using the EUROGAM2 array. In Tc109 we have found a new band corresponding to the π5/2⊃-[303] configuration and a three-quasiparticle band with Iπ=(15/2⊃-) band-head level at 1749.5 keV. The structure of the 1749.5-keV level probably involves the {π5/2⊃+[422] ν(5/2⊃-[532],5/2⊃+[413])}15⊃/2⊃- prolate configuration. The quasiparticle-rotor model calculations performed in this work show that the odd-proton configurations observed in Tc107 and Tc109 are consistent with the scheme of proton excitations in a prolate triaxial potential. Significant differences between the degree of triaxiality observed for positive- and negative-parity excitations may be due to blocking of the triaxial shape by the odd proton populating negative-parity orbitals. The properties of the new 494.5-, 1440.7-, and 1748.8-keV levels found in Tc109 may indicate a change toward an oblate shape in this nucleus. © 2010 The American Physical Society.