Fission studies using multi-nucleon transfer reactions

Nishio, Katsuhisa   

Using the JAEA tandem accelerator facility in Tokai, we are promoting a program of fission studies using multi-nucleon transfer (MNT) reactions. The MNT reaction allows us to produce neutron-rich actinide nuclei, which cannot be populated by particle capture reactions. Fission fragment mass distributions (FFMDs) for various nuclei were obtained. The FFMDs and their evolution with initial excitation energies were explained only by invoking a concept of multi-chance fission, i.e. neutron-evaporation before fission. From the fission probabilities plotted as a function of the excitation energy, the fission barrier height was derived. The obtained data set was used to improve the Langevin model to describe low-energy fissions, which resulted in a clear explanation of the transition from the mass-asymmetric fission to the sharp symmetric fission observed in the fermium isotopes. Recently, we obtained the Es target material from the Oak Ridge National Laboratory, US, and have carried out experiments on low-energy fissions in the fermium region. New results will be discussed.