Level structure of 120Cs

Abstract

Excited states of the 120Cs nucleus have been studied by using in-beam γ-ray spectroscopy with the 107Ag( 16O, 3n) 120Cs fusion–evaporation reaction at a beam energy of 85 MeV. The level scheme of 120Cs has been determined using γ– γ coincidence and γ– γ angular correlation analyses. We suggest that the spin of the lowest state for the πh 11/2⊗ νh 11/2 quasiparticle band should be 9 +, which is 2ℏ higher in angular momentum than that of previous spin assignment. A spin inversion between the favored and the unfavored states in this positive-parity band was observed below I=19ℏ. In addition, the spin assignment of the negative-parity band with small signature splitting has also been made for the band head with I π =8 −. These two rotational bands are found to be connected to each other at lower spin states and to the high-spin 7 − isomer with half-life of T 1/2=61.2 s through different decay paths.