Recent advances in modeling fission cross sections over intermediate structures

More accurate fission cross section calculations in presence of underlying intermediate structure are strongly desired. This paper recalls the common approximations used below the fission threshold and quantifies their impact. In particular, an exact expanded R-matrix Monte Carlo calculation of the intermediate structure, deeply mixed with the fluctuations of the class-I and II decay amplitudes, is shown. This paper also insists on the microscopic structure of the level densities as a function of the nucleus deformation and show preliminary neutron induced fission cross section calculations for 239Pu and 240Pu using newly calculated combinatorial level densities. Comparisons with recent evaluated and measured fission cross sections are made.