DOI: 10.1051/ndata:07680 Dynamical approach to scission-neutron emission in low energy fission

Abstract. At a certain neck radius during the descent of a fissioning nucleus from the saddle to the scission point, the attractive nuclear forces can no more withstand the repulsive Coulomb forces producing the neck rupture and the sudden absorbtion of the neck stubs by the fragments. At that moment, the neutrons, although still characterized by their pre-scission wave functions, find themselves in the newly created potential of their interaction with the separated fragments. Their wave functions become wave packets with components in the continuum. The probability to populate such states gives evidently the emission probability of neutrons at scission. In this way we have studied scission neutrons for 236U, using two-dimensional realistic nuclear shapes. We have first calculated symmetric fission. Both the emission probability and the distribution of the emission points relative to the fission fragments strongly depend on the quantum numbers of the pre-scission state from which the neutron is emitted. In particular it was found that states with Ωπ = 1/2+ dominate the emission. Depending on the assumed pre- and post-scission configurations and on the emission barrier height, 30 % to 50 % of the total scission neutrons are emitted from 1/2+ states. Their emission points are concentrated in the region between the newly separated fragments. The upper limit for the total number of neutrons per scission event is predicted to lie between 0.16 and 1.73 (depending on the computational assumptions). A sudden transition not only produces scission neutrons but also leaves the fission fragments in an excited state. The corresponding excitation energy was estimated. Then we have investigated the dependence on the mass ratio of th