Subbarrier fission probabilities of Pu-240

In the framework of the optical model for fission a general expression for the fission probability is obtained, an expression valid in a wide energy range. The code PROBFIS based on this model was used to calculate prompt and isomeric fission probabilities and the fission half life of the shape isomer. From the comparison of these calculations with the corresponding experimental data the parameters of the fission barriers associated with the discrete transitional states of Pu-240 have been determined. These parameters satisfy the constraints imposed by the different symmetries of the shape of the nucleus at the saddle points and their values are in agreement with the existing statistics. (C) 1997 Elsevier Science Ltd.