Fission dynamics of Cf 252

Static and dynamic aspects of the fission process of 226 Th are analyzed in a self-consistent framework based on relativistic energy density functionals. Constrained relativistic mean-field (RMF) calculations in the collective space of axially symmetric quadrupole and octupole deformations, based on the energy density functional PC-PK1 and a δ-force pairing, are performed to determine the potential energy surface of the fissioning nucleus, the scission line, the single-nucleon wave functions, energies and occupation probabilities, as functions of deformation parameters. Induced fission dynamics is described using the time-dependent generator coordinate method in the Gaussian overlap approximation. A collective Schrödinger equation, determined entirely by the microscopic single-nucleon degrees of freedom, propagates adiabatically in time the initial wave packet built by boosting the ground-state solution of the collective Hamiltonian for 226 Th. The position of the scission line and the microscopic input for the collective Hamiltonian are analyzed as functions of the strength of the pairing interaction. The effect of static pairing correlations on the pre-neutron emission charge yields and total kinetic energy of fission fragments is examined in comparison with available data, and the distribution of fission fragments is analyzed for different values of the initial excitation energy. * Electronic address: zpliphy@swu.edu.cn A microscopic description of fission presents one of the most complex problems in lowenergy theoretical nuclear physics [1, 2]. For a comprehensive recent review and an exhaustive list of references, we refer the reader to Ref. [1]. The spontaneous or induced fission process in which a heavy nucleus splits into fragments is out of reach for ab initio methods and, therefore, modern microscopic approaches are based on the framework of nuclear energy density functionals (NEDFs). Nuclear density functional theory (DFT) and its timedependent (TD) generalization have enabled a self-consistent treatment of both static and dynamic aspects of fission [3-11]. The slow large-amplitude collective motion of the compound system that eventually leads to the formation of the final fragments can be described, in a first approximation, as an adiabatic process in which the intrinsic nucleonic degrees of freedom are decoupled from macroscopic collective degrees of freedom such as multipole moments (deformations) of the mass distribution and pairing fields [1].Numerous studies of spontaneous fission, based on NEDFs, have analyzed the effects of the choice of collective coordinates (shape degrees of freedom), approximations used to calculate the collective inertia, and coupling between shape and pairing degrees of freedom on fission half-lives [12][13][14][15][16][17][18]. A quantitative description of induced fission is, in this framework, conceptually and computationally more challenging and this process has been explored less systematically. In particular, several recent studies have used the time-dependent gener...

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confidence: 99%

Microscopic study of induced fission dynamics of Th226 with covariant energy density functionals

Tao

Zhao

et al. 2017

“…It is for example impossible to describe the tunneling in fusion or fission reactions. 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.…”

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confidence: 99%

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

Scamps

Hashimoto

2017

The transfer reaction between two nuclei in the superfluid phase is studied with the Timedependent Hartree-Fock-Bogoliubov (TDHFB) theory. In order to restore the symmetry of the relative gauge angle a set of independent TDHFB trajectories is taken into account. Then, the transfer probability is computed using a triple projection method. This method is first tested to determine the transfer probabilities on a toy model and compared to the exact solution. It is then applied to the reactions 20 O+

“…The impact of the choice of the initial state on tdgcm+goa yields has already been explored in the fission of 240 Pu and 252 Cf in Ref. [30,31]. In these two cases, the characteristics of the main fission mode were not drastically affected by initializing the dynamics with different types of collective states (boosted Gaussian, Gaussian or Fermi mixing of eigen-modes of an extrapolated first potential well).…”

Section: B Initial Statementioning

confidence: 99%

From asymmetric to symmetric fission in the fermium isotopes within the time-dependent generator-coordinate-method formalism

Regnier

Dubray

Schunck³

2019

Background: Predicting the properties of neutron-rich nuclei far from the valley of stability is one of the major challenges of modern nuclear theory. In heavy and superheavy nuclei, a difference of only a few neutrons is sufficient to change the dominant fission mode. A theoretical approach capable of predicting such rapid transitions for neutron-rich systems would be a valuable tool to better understand r-process nucleosynthesis or the decay of super-heavy elements.Purpose: In this work, we investigate for the first time the transition from asymmetric to symmetric fission through the calculation of primary fission yields with the time-dependent generator coordinate method (tdgcm). We choose here the transition in neutron-rich Fermium isotopes, which was the first to be observed experimentally in the late seventies and is often used as a benchmark for theoretical studies. Methods:We compute the primary fission fragment mass and charge yields for 254 Fm, 256 Fm and 258 Fm from the tdgcm under the Gaussian overlap approximation. The static part of the calculation (generation of a potential energy surface) consists in a series of constrained Hartree-Fock-Bogoliubov calculations based on the d1s, d1m or d1n parameterizations of the Gogny effective interaction in a two-center harmonic oscillator basis. The 2dimensional dynamics in the collective space spanned by the quadrupole and octupole moments (Q20,Q30) is then computed with the finite element solver Felix-2.0.Results: The available experimental data and the tdgcm post-dictions are consistent and agree especially on the position in the Fermium isotopic chain at which the transition occurs. In addition, the tdgcm predicts two distinct asymmetric modes for the fission of 254 Fm.Conclusions: Thanks to its intrinsic accounting of shell effects and to its ability to describe the dynamics of the system up to configurations close to scission, the tdgcm is able to describe qualitatively the fission yield transition in the neutron-rich Fermium isotopes. This makes it a promising tool to study the evolution of the fission yields far from the valley of stability. The main limitation of the method lies in the presence of discontinuities in the 2-dimensional manifold of generator states.