Dynamical scission model

Abstract

A time-dependent microscopic approach to the scission process, i.e., the transition from two fragments connected by a thin neck (αi) to two separated fragments (αf), which takes place in a short time interval ΔT, is presented. We follow the evolution from αi to αf of all occupied neutron states by solving numerically the two-dimensional time-dependent Schrödinger equation with time-dependent potential. Calculations are performed for mass divisions from AL=70 to AL=118 (AL being the light-fragment mass). The duration of the neck rupture ΔT is taken as parameter having values from 0.25×10−22 to 6×10−22s. The resulting scission-neutron multiplicities νsc and primary fragment excitation energies Esc⁎ are compared with those obtained in the frame of the sudden approximation (ΔT=0). As expected, the sudden approximation is an upper limit. For ΔT=10−22s, which is a realistic value, the time-dependent results are 15% to 20% below this limit. For transition times longer than 6×10−22s the adiabatic limit is reached. The probability and current densities of the unbound neutrons at scission are also calculated. They provide a detailed picture of the emission mechanism and a hint for the angular distribution of the scission neutrons with respect to the fission axis.