Collective band structures in the Tc-99 nucleus

Excited states in Tc-99 with energies up to 6 MeV have been populated using the Zr-96(Li-7, 4n)Tc-99 reaction with a laboratory beam energy of 35 MeV. Coincident gamma rays from excited nuclei produced in the reactions were detected using an array of coaxial, planar, and clover-type high-purity germanium detectors. A total of 60 new gamma-ray transitions and 21 new levels are identified and placed into a new level scheme. Two collective bands assigned to be built on the pi g(9/2)[422]5/2(+) and pi p(1/2)[301]1/2(-) Nilsson configurations have been extended with spins up to 35/2 and 33/2 h, respectively. Backbending and signature inversion have been observed in the yrast band. The large signature splitting of the positive-parity band in Tc-99 may be caused by a triaxial deformation, which agrees well with the electromagnetic properties, theoretical calculations based on total Routhian surface, and triaxial particle-rotor model calculations.