Fission dynamics within time-dependent Hartree-Fock: Deformation-induced fission

Abstract

Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic density functional studies of fission have previously concentrated on adiabatic approaches based on constrained static calculations ignoring dynamical excitations of the fissioning nucleus and the daughter products.Purpose: We explore the ability of dynamic mean-field methods to describe fast fission processes beyond the fission barrier, using the nuclide 240 Pu as an example.Methods: Time-dependent Hartree-Fock calculations based on the Skyrme interaction are used to calculate nonadiabatic fission paths, beginning from static constrained Hartree-Fock calculations. The properties of the dynamic states are interpreted in terms of the nature of their collective motion. Fission product properties are compared to data.Results: Parent nuclei constrained to begin dynamic evolution with a deformation less than the fission barrier exhibit giant-resonance-type behaviour. Those beginning just beyond the barrier explore large amplitude motion but do not fission, whereas those beginning beyond the two-fragment pathway crossing fission to final states which differ according to the exact initial deformation.Conclusions: Time-dependent Hartree-Fock is able to give a good qualitative and quantitative description of fast fission, provided one begins from a sufficiently deformed state.

Fission fragment charge and mass distributions inPu239(n,f)in the adiabatic nuclear energy density functional theory

“…The eigenstates g k (q) with the lowest energies are all localized at low deformation and contain different phonons in theQ 20 and/orQ 30 degrees of freedom. In practice, we determine the first 100 of them using a Krylov-Schur algorithm implemented in the SLEPc library [49].…”

“…This approach automatically includes onebody dissipation effects: as the nucleus changes its shape, single-particle excitations (or quasi-particle excitations when pairing correlations are taken into account) are included, which slows the collective motion. TDDFT is probably the most promising approach to describe the structure of the fission fragments and various recent works have shown extremely encouraging results [19][20][21][22]. However, realistic simulation of a single fission event including full symmetry breaking and full treatment of pairing correlations is at the limit of what current supercomputers can handle [22].…”

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

“…The Hartree-Fock approximation and its time-dependent generalization, the time-dependent Hartree-Fock theory, have provided a possible means to study the diverse phenomena observed in low energy nuclear physics [41,42]. In general modern TDHF calculations provide a useful foundation for a fully microscopic many-body description of large amplitude collective motion including collective surface vibrations and giant resonances [48][49][50][51][52][53][54][55][56][57][58][59][60][61] nuclear reactions in the vicinity of the Coulomb barrier, such as fusion [36,39,[62][63][64][65][66][67][68][69], deepinelastic reactions and transfer [70][71][72][73][74][75][76], and dynamics of (quasi)fission fragments [33,[43][44][45][46][47].…”

“…In particular, the time-dependent Hartree-Fock theory [40], has been recognized for its realistic description of several low-energy nuclear reaction mechanisms [41,42]. It has been recently utilized for studying the dynamics of quasifission [25,33,43,44] and scission [45][46][47]. The study of quasifission is showing a great promise to provide insight based on very favorable comparisons with experimental data [25,33].…”

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].…”