New level schemes of odd-$Z$ ${}^{105,107,109}\mathrm{Tc}$ are proposed based on the ${}^{252}\mathrm{Cf}$ spontaneous-fission-gamma data taken with Gammasphere in 2000. Bands of levels are considerably extended and expanded to show rich spectroscopic information. Spin/parity and configuration assignments are made based on determinations of multipolarities of low-lying transitions and the level analogies to the previously reported levels, and to those of the neighboring $\mathrm{Rh}$ isotopes. A non-yrast negative-parity band built on the $3∕2^{-}\left[301\right]$ orbital is observed for the first time in ${}^{105}\mathrm{Tc}$. A positive-parity band built on the $1∕2^{+}\left[431\right]$ intruder orbital originating from the $\pi \left(g_{7∕2}∕d_{5∕2}\right)$ subshells and having a strong deformation-driving effect is observed for the first time in ${}^{105}\mathrm{Tc}$, and assigned in ${}^{107}\mathrm{Tc}$. A positive-parity band built on the excited $11∕2^{+}$ level, which has rather low excitation energy and predominantly decays into the $9∕2^{+}$ level of the ground state band, provides evidence of triaxiality in ${}^{107,109}\mathrm{Tc}$, and probably also in ${}^{105}\mathrm{Tc}$. Rotational constants are calculated and discussed for the $K=1∕2$ intruder bands using the Bohr-Mottelson formula. Level systematics are discussed in terms of the locations of proton Fermi levels and deformations. The band crossings of yrast positive-parity bands are observed, most likely related to $h_{11∕2}$ neutron alignment. Triaxial-rotor-plus-particle model calculations performed with $\epsilon =0.32$ and $\gamma =-22.5°$ on the prolate side of maximum triaxiality yielded the best reproduction of the excitation energies, signature splittings, and branching ratios of the positive-parity bands (except for the intruder bands) of these $\mathrm{Tc}$ isotopes. The significant discrepancies between the triaxial-rotor-plus-particle model calculations and experiment for the $K=1∕2$ intruder bands in ${}^{105,107}\mathrm{Tc}$ need further theoretical studies.

• Received 28 May 2004

DOI:https://doi.org/10.1103/PhysRevC.70.044310