Monoisotopic samples of ${}^{109}$Mo nuclei, produced in the deuteron-induced fission of ${}^{238}$U and separated using the IGISOL mass separator coupled to a Penning trap, were used to perform $\beta$- and $\gamma$-coincidence spectroscopy of ${}^{109}$Tc. Spin and parity 5/2${}^{+}$ for the ground state of ${}^{109}$Mo, proposed earlier, are supported in the present work. Three new low-energy levels observed in ${}^{109}$Tc are interpreted as bandheads of the $\pi 3/2^{-}$[301], $\pi 5/2^{-}$[303], and $\pi 1/2^{+}$[431] configurations, respectively. A further three levels observed around 0.4 MeV are interpreted as $K=1/2$ triaxial excitations. A similar interpretation is proposed for an analogous set of three levels observed in ${}^{107}$Tc in another ${\beta }^{-}$ decay work. The systematics of these excitations breaks down in ${}^{111}$Tc, most likely due to a transition from prolate to oblate deformation. An excitation at 745.0 keV in ${}^{109}$Tc and 850.7 keV in ${}^{107}$Tc is interpreted as the $\pi$7/2${}^{+}$[413] configuration. Quasiparticle-rotor model calculations support the proposed interpretations.

• Received 29 August 2012

DOI:https://doi.org/10.1103/PhysRevC.86.044306