Speaker: Walid Younes (Lawrence Livermore Natl Lab)

Fission models for actinide (n,f) cross sections

The (n,f) cross section on a variety of actinides of interest cannot be easily measured in the laboratory, because the target is too short-lived. For example, there is no reliable measurement of the 237U(n,f) cross section up to En = 20 MeV. Using surrogate (t,pf), (3He,df), and (3He,tf) reactions to populate the same compound system as the neutron-induced reaction of interest, the (n,f) cross section up to a few MeV's for various Th, U, Np, Pu, and Am targets has been estimated. Standard reaction models were used to account for the differences in population by the surrogate (e.g., (t,pf)) and neutron-induced reactions. The same standard fission model was used to describe the fission process common to both reactions. I will present these estimated cross sections and discuss a preliminary extension of the 237U(n,f) cross section up to En = 20 MeV in a simplified approach. In order to extend the present (n,f) estimates up to En = 20 MeV within a more robust framework, I will discuss planned improvements to the current fission model to include: the angular-momentum and temperature dependence of the potential surface, the coupling between intrinsic and collective degrees of freedom, and the dynamical aspects of fission via a diffusion-model approach. Finally, I will explore the prospects for a fully microscopic calculation of actinide (n,f) cross sections. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.