The structure of the deformed nucleus 42 103 Mo61

Abstract

The lifetimes of the three lowest excited members of the rotational ground-state band of103Mo at 102.6, 241.1 and 433.2 keV as well as of the levels at 353.8 and 456.1 keV have been determined through a measurement of the delayed coincidences betweenβ particles from the decay of the parent103Nb and theγ rays which depopulate the levels. A plastic and a BaF2 detector have been used for theβ andγ rays, respectively, in these experiments at the fission product separator JOSEF. The results for all three band members evince that this nucleus has a sizeable deformation, with a value ofβ q=0.34(1). This value is larger than that of the neighbouring even-even Mo isotopes which indicates an odd-even effect. On the other hand it confirms the observation that the Mo nuclei are in general less strongly deformed than their Sr and Zr isotones. Particle-rotor model calculations with the Nilsson parametersκ=0.084,μ=0.28 provide a good description of the ground-state band and of a side band based on the 346.5 keV level, including the new lifetimes. This substantiates the Nilsson orbital assignments of [411]3/2+ and [532]5/2− for these two bands, respectively, where the sideband is strongly affected by a [541]3/2− admixture. There is evidence for an additional band based on the 641.1 keV level for which the assignment [422]3/2+ is proposed.