Intermediate structure and the shape isomer in 233Th

Abstract

With a neutron-capture experiment the s-wave resonances in 233Th between 50 eV and 4.2 keV were investigated for delayed γ-γ coincidences. At least two intermediate structures are found in the distribution of the relative delayed γ-yield R at about 1 and 2 keV incident neutron energy confirmed by statistical tests. We interpret them as being due to the population of a shape-isomeric state via class-II states admixed to the resonances. From the derived class-II spacing DII and the gross shape of the structures the isomeric ground-state energy EII as well as the coupling width Γ↓ may then be estimated. These results are compatible with the decay of a shape isomer with a half life between 1 and 100 ns. They also would suggest that the height of the inner potential barrier EA is less than or of the order of the neutron binding energy, and that the inner barrier is relatively thin.