Excited states in ${}^{99}\mathrm{Tc}$ with energies up to 6 MeV have been populated using the ${}^{96}\mathrm{Zr}({}^7\mathrm{Li},4n){}^{99}\mathrm{Tc}$ 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 $\pi g_{9/2}\left[422\right]5/2{}^{+}$ and $\pi p_{1/2}\left[301\right]1/2{}^{-}$ Nilsson configurations have been extended with spins up to 35/2 and $33/2 \hslash$, respectively. Backbending and signature inversion have been observed in the yrast band. The large signature splitting of the positive-parity band in ${}^{99}\mathrm{Tc}$ 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.

• Received 21 November 2014
• Revised 20 March 2015

DOI:https://doi.org/10.1103/PhysRevC.91.054314