N. Carjan

Multi-dimensional Langevin approach to fission dynamics

Abstract Multi-dimensional Langevin approach to nuclear dissipative phenomena is presented. We solve two-dimensional Langevin equation numerically without any approximations for the study of induced fission dynamics. Transient time of the symmetric fission of 213At is calculated and discussed in comparison with empirically deduced value. Fragment kinetic energy distribution is calculated and compared with experiments.

Emission of scission neutrons in the sudden approximation

At a certain finite 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 absorption 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 the fissioning nucleus

Two‐dimensional Langevin approach to nuclear fission

^{236}

One-body dissipation in agreement with prescission neutrons and fragment kinetic energies

U, using two-dimensional realistic nuclear shapes. 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

Dynamical scission model

\Omega \pi

Cassini-oval Description of the Energy Balance at Scission During 235U(nth, f)

= 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).

Scission Configurations for StI and StII Fission Modes in the Reaction 235U(nth, f)

The bidimensional Langevin for the symmetric fission of 213At were solved without approximations using computer generated stochastic forces. Two dissipation mechanisms have been studied: a typical weak one (hydrodynamical viscosity) and a typical strong one (energy transferred to nucleonic motions from their changing self consistent potential). Calculated transient times (2.10−20 sec or less) are comparable with those extracted from measurements of prescission neutron multiplicity. The kinetic energy distribution of the fission fragments was calculated for nuclear temperatures T=1,2 and 3 MeV. A good agreement between theory and experiment was found for the variation with T of both its mean value and its variance. The calculated absolute values are however slightly lower than the empirical ones. At the same time it was also possible to test the validity of a deterministic (Lagrange) approach to the mean value of the prescission kinetic energy. The error involved was found to decrease with increasing T and...