Dynamic excitation in the fission of 240Pu

The excitation mechanism of the fission process is studied in terms of a model of particles moving in a deformed time-dependent potential. A residual interaction of the pairing type is incorporated by means of the BCS approximation. No limitations are imposed on the number of quasiparticles. The calculations of the dynamical variables are done by solving numerically the equation of motion of the quasiparticle density and pairing matrices. The set of quasiparticle states is truncated by an energy cutoff. The effects of this cutoff on the results are negligible. Comparison with calculations for 240Pu which were restricted to two-quasiparticle excitations only shows that this restriction results in an appreciable underestimate of the total excitation energy. The estimated collective energy is found to be at least one order of magnitude smaller than the dissipated energy for an oscillatory motion of the collective coordinates