Role of transitional levels in 237Np (γ,f):: Perspectives for studying highly deformed systems

The transition levels at the top of the two Np-237 fission barriers were obtained for the first time by means of the so-called semimicroscopic combined method, which we have developed and implemented. To overcome the difficulties in dealing with large nuclear deformations, we used our developed BARRIER code, which calculates single-particle spectra in a deformed Woods-Saxon potential using a coordinate system based on Cassini ovaloids as nuclear shape parametrization. The results enabled us to describe the experimentally observed near-barrier photofission cross-section structures for Np-237, as well as a subbarrier shelf, the latter being consistently interpreted in terms of the accumulation of levels at the top of the inner and outer double fission barrier of Np-237.