Mass and nuclear charge yields for 237Np(2n th,f) at different fission fragment kinetic energies

Abstract

The recoil mass separator LOHENGRIN of the Laue-Langevin Institute Grenoble has been used to measure for the first time, the yields of light fission fragments from the fissioning system: 239 93Np; this odd-Z nucleus is formed after double thermal neutron capture in a 239 93Np target. The mass distributions were measured for different kinetic energies between 92 and 115.5 MeV, but the nuclear charge distributions were determined only up to 112 MeV. These distributions are compared to the distributions obtained for the even-even system 240 94Pu. At high kinetic energy, the mass distribution shows a prominent peak around mass number A L = 106. These cold fragmentations are discussed in terms of a calculation based on a scission point model extrapolated to the cold fission case. As expected for an odd- Z fissioning nucleus, the nuclear charge distributions do not reveal any odd-even effect. The global neutron odd-even effect is found to be (8.1 ± 1.5)%. A simple model has been used to show that most of the neutron odd-even effect results from prompt neutron evaporation from the fragments.