First step towards a non-adiabatic description of the fission process based on the Generator Coordinate Method

Among the different theoretical approaches able to describe fission, micr oscopic ones can help us in the understanding of this process, as they have the advant age of describing the nuclear structure and the dynamics in a consistent manner. The sole input of the calculations is the nucleon-nucleon interaction. Such a microscopic time-dependent and quantum mechanical formalism has already been used, based on the Gaussian Overlap Approximation of the Generator Coordinate Method with the adiabatic approximation, to analyze the collective dynamics of low-energy fission in 238 U (1). However, at higher energies, a few MeV above the barrier, the adiabatic approximation doesn't seem valid anymore. In deed, manifestations of proton pair breaking have been observed in 238 U and 239 U for an excitation energy of 2.3 MeV above the barrier (2-4). Taking the intrinsic excitations into account during the fission process will ena ble us to determine the coupling between collective and intrinsic degrees of freedom, in particular from saddle to scission. Guidelines of the new formalism under development are presented and some preliminary results on overlaps between non excited and excited states are discussed.