Shape evolution and collective dynamics of quasifission in the time-dependent Hartree-Fock approach

Abstract

Background: At energies near the Coulomb barrier, capture reactions in heavy-ion collisions result either in fusion or in quasifission. The former produces a compound nucleus in statistical equilibrium, while the second leads to a reseparation of the fragments after partial mass equilibration without formation of a compound nucleus. Extracting the compound nucleus formation probability is crucial to predict superheavy-element formation crosssections. It requires a good knowledge of the fragment angular distribution which itself depends on quantities such as moments of inertia and excitation energies which have so far been somewhat arbitrary for the quasifission contribution.Purpose: Our main goal is to utlize the time-dependent Hartee-Fock (TDHF) approach to extract ingredients of the formula used in the analysis of experimental angular distributions. These include the moment-of-inertia and temperature.Methods: We investigate the evolution of the nuclear density in TDHF calculations leading to quasifission. We study the dependence of the relevant quantities on various initial conditions of the reaction process.Results: The evolution of the moment of inertia is clearly non-trivial and depends strongly on the characteristics of the collision. The temperature rises quickly when the kinetic energy is transformed into internal excitation. Then, it rises slowly during mass transfer.Conclusions: Fully microscopic theories are useful to predict the complex evolution of quantities required in macroscopic models of quasifission.

Multinucleon transfer in central collisions of U238+U238

“…A number of models was developed for a description of the reaction mechanism in the multi-nucleon transfer process in quasi-fission reactions [1][2][3][4]. Within the last few years the time-dependent Hartree-Fock (TDHF) approach [5][6][7] has been utilized for studying the dynamics of quasifission [7][8][9][10][11][12][13][14][15][16][17] and scission dynamics [18][19][20][21][22][23]. Such calculations are now numerically feasible to perform on a 3D Cartesian grid without any symmetry restrictions and with much more accurate numerical methods [24][25][26].…”

Transfer probabilities for the reactions O14,20+O20 in terms of multiple time-dependent Hartree-Fo

“…For fission, the Time-dependent Generator Coordinate Method (TDGCM) [12][13][14] solves partially this problem but assumes a collective motion in a space of adiabatic basis. On the other hand, for fusion tunneling, the Densityconstraint Hartree-Fock [15,16] is restrained to a single energy-dependent fusion path.…”

Dynamical effects in fusion with exotic nuclei

“…The starting distance must be large enough so that Coulomb excitation is properly accounted for in the approach phase. This is particularly important for calculations involving large charge products Z 1 Z 2 [77,78]. Starting at a separation distance between the centres of masses of 44.8 fm is large enough to account for this effect in Ca+Sn collisions.…”