Collective band structures in the 99Tc nucleus

Excited states in ⁹⁹Tc with energies up to 6 MeV have been populated using the ⁹⁶Zr(⁷Li,4 n )⁹⁹Tc reaction with a laboratory beam energy of 35 MeV. Coincident γ 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 γ -ray transitions and 21 new levels are identified and placed into a new level scheme. Two collective bands assigned to be built on the π g_{9 /2} [422 ]5 /2 ⁺ and π p_{1 /2} [301 ]1 /2 ^- Nilsson configurations have been extended with spins up to 35/2 and 33 /2 ℏ , respectively. Backbending and signature inversion have been observed in the yrast band. The large signature splitting of the positive-parity band in ⁹⁹Tc 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.