Low-spin excitations in the 109Tc nucleus

Monoisotopic samples of 109Mo nuclei, produced in the deuteron-induced fission of 238U and separated using the IGISOL mass separator coupled to a Penning trap, were used to perform β- and γ -coincidence spectroscopy of 109Tc. Spin and parity 5/2+ for the ground state of 109Mo, proposed earlier, are supported in the present work. Three new low-energy levels observed in 109Tc are interpreted as bandheads of the π3/2−[301], π5/2−[303], and π1/2+[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 107Tc in another β− decay work. The systematics of these excitations breaks down in 111Tc, most likely due to a transition from prolate to oblate deformation. An excitation at 745.0 keV in 109Tc and 850.7 keV in 107Tc is interpreted as the π7/2+[413] configuration. Quasiparticle-rotor model calculations support the proposed interpretations.