INTERMEDIATE STRUCTURE AND THE SHAPE ISOMER IN TH-233

With a neutron-capture experiment the s-wave resonances in Th-233 betw een 50 eV and 4.2 keV were investigated for delayed gamma-gamma coinci dences. At least two intermediate structures are found in the distribu tion of the relative delayed gamma-yield R at about 1 and 2 keV incide nt neutron energy confirmed by statistical tests. We interpret them as being due to the population of a shape-isometric state via class-II s tates admixed to the resonances. From the derived class-II spacing D(I I) and the gross shape of the structures the isomeric ground-state ene rgy E(II) as well as the coupling width GAMMA(down) may then be estima ted. These results are compatible with the decay of a shape isomer wit h a half life between 1 and 100 ns. They also would suggest that the h eight of the inner potential barrier E(A) is less than or of the order of the neutron binding energy, and that the inner barrier is relative ly thin.