Scission shapes of pair fragments in asymmetric and symmetric fission modes

Scission shapes composed of two touching spheroids in asymmetric and symmetric fission modes have been deduced from static potential calculations with the experimental fragment total kinetic energy and excitation energies for a typical fragment pair of ¹⁰³Nb and ¹³⁰Sn in the proton-induced fission of ²³²Th. It was found that the fragment deformation of the heavy fragment ¹³⁰Sn in the symmetric fission mode was extremely large compared with that in the asymmetric fission and those of the complementary fragment ¹⁰³Nb. Such scission shapes also provide internal excitation energies of pair fragments in the two fission modes. The deduced total internal excitation energies of complementary fragments for the two fission modes are nearly the same as the excitation energy of the fissioning nucleus. The results suggest that the two fission modes are strongly characterized by the degrees of fragment deformation of the heavy fragments, not by the total internal excitation energies at scission.