Fine structure of the 0 . 7 MeV resonance in the 230 Th neutron – induced cross section Short title : Fine structure in neutron - induced fission

– The fine structure of the 0.7 MeV resonance in the 230 Th neutron-induced cross section is investigated within the hybrid model. A very good agreement with experimental data is obtained. It is suggested that fine structure of the cross section quantify the changes of the intrinsic states of the nucleus during the disintegration process. Introduction. – The neutron-induced cross sections of 230,232 Th exhibit multiple fine structures [1, 2] superimposed on a gross structure of the threshold cross section. If the fine structure is interpreted as a series of rotational states constructed on a β-vibrational state produced in some well of the multidimensional barrier, it is straightforward to postulate the existence of a triple humped barrier. The spacing between the members of the band is so small that it is consistent only with a parent nucleus with prolate deformation that reaches the vicinity of the second barrier top. Therefore, a shallow minimum can be expected at this deformation to create a β-vibrational state. Up to now, the assumption of a triple humped barrier seems to be the best interpretation for the fine structure of intermediate cross section resonances [3]. The principal aim of the present work is to offer an alternative explanation of this phenomenon by taking into account dynamical single-particle effects. Recently, a Hybrid Model (HM) [4] was developed in order to investigate the intermediate structure of the fission cross section. In the frame of the HM, the excited states during the deformation process of the parent nucleus and their realization probabilities must be obtained. The occupations of the excited states are determined theoretically by solving microscopic equations of motion. These excited states are added to a phenomenological double humped barrier and new barriers with different shapes are constructed. The energy width in the fission channel is proportional to the weighted summation of the penetrabilities of these barriers. The fine structure of the 0.7 MeV resonance of the 230 Th neutron-induced cross section is studied within our model.