Symmetric Fission Observed in Thermal-Neutron-Induced and Spontaneous Fission ofFm257

Abstract
The observed mass distribution for thermal-neutron-induced fission of Fm257 is strongly symmetric, whereas that for spontaneous fission of Fm257 is found to be predominantly asymmetric with, however, some symmetric fission present. The mass distributions were derived from energy measurements on coincident fission fragments. The onset of symmetric fission at Fm257 supports theories relating asymmetric fission to the second hump of the fission barrier.