Collective band structures in theTc99nucleus

Excited states in $^{99}\mathrm{Tc}$ with energies up to 6 MeV have been populated using the $^{96}\mathrm{Zr}(^{7}\mathrm{Li},\phantom{\rule{0.16em}{0ex}}4n)^{99}\mathrm{Tc}$ reaction with a laboratory beam energy of 35 MeV. Coincident $\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}$-ray transitions and 21 new levels are identified and placed into a new level scheme. Two collective bands assigned to be built on the $\ensuremath{\pi}{g}_{9/2}[422]5/2{}^{+}$ and $\ensuremath{\pi}{p}_{1/2}[301]1/2{}^{\ensuremath{-}}$ Nilsson configurations have been extended with spins up to 35/2 and $33/2 \ensuremath{\hbar}$, 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.