Fission-fragment charge distributions in thermal-neutron induced fission of 239Pu and 235U

Abstract

Fission-fragment charge distributions of heavy fragments were investigated for fragment masses 131 ≦ A ≦ 140 in the reactions 239Pu(n th, f) and 235U(n th, f). This was done by a correlated observation of β-tracks and fission-fragment tracks in nuclear emulsions for fission fragments separated with respect to mass and kinetic energy by a recoil mass spectrograph. The average nuclear charges are almost identical for both fissioning nuclei in the fragment mass range investigated. Specifically, for both systems the yields of the doubly magic 50 132Sn 82 appear to be enhanced. Both observations again support the hypothesis that in low-excitation fission of the actinides the nuclear structure of the heavy fragment plays a predominant role.