Near-yrast, medium-spin structure of theMo107nucleus

Abstract

Excited levels in the {sup 109}Tc nucleus, populated in the spontaneous fission of {sup 248}Cm, have been studied using the EUROGAM2 array. In {sup 109}Tc we have found a new band corresponding to the {pi}5/2{sup -}[303] configuration and a three-quasiparticle band with I{sup {pi}}=(15/2{sup -}) band-head level at 1749.5 keV. The structure of the 1749.5-keV level probably involves the {l_brace}{pi}5/2{sup +}[422]{nu}(5/2{sup -}[532],5/2{sup +}[413]){r_brace}{sub 15/2}{sup -} prolate configuration. The quasiparticle-rotor model calculations performed in this work show that the odd-proton configurations observed in {sup 107}Tc and {sup 109}Tc 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 {sup 109}Tc may indicate a change toward an oblate shape in this nucleus.