Microscopic approach of fission dynamics applied to fragment kinetic energy and mass distributions inU238

Abstract

The collective dynamics of low-energy fission in 238 U is described within a time-dependent formalism based on the Gaussian overlap approximation of the time-dependent generator coordinate method. The intrinsic deformed configurations of the nucleus are determined from the self-consistent Hartree-Fock-Bogoliubov procedure employing the effective force D1S with constraints on the quadrupole and octupole moments. Fragment kinetic energy and mass distributions are calculated and compared with experimental evaluations. The effect of the collective dynamics along the fission paths and the influence of initial conditions on these distributions are analyzed and discussed.

Nuclear energy density optimization: Large deformations

“…[5][6][7][8][9][10]), Gogny (see, e.g., Refs. [11][12][13][14]), and relativistic (see, e.g., Refs. [5,15,16]) energy density functionals (EDFs).…”

Fragment Yields Calculated in a Time-Dependent Microscopic Theory of Fission

“…Nuclear fission in particular, has been studied using microscopic approaches since the 1980's (e.g., [4,6,7,5,8]). For the present work, we have adopted the Bohr approximation to the Time-Dependent Generator Coordinate Method (TDGCM), successfully used by Berger et al [4] and Goutte et al [6] to calculate fission as the propagation of a collective wave packet built on microscopic nuclear states and representing the fissioning nucleus as it moves toward scission. These earlier calculations were used to examine properties such as the fission time scale, and the mass distribution of fission fragments.…”

“…The same D1S finite-range interaction [14,15] has been used for both reactions and for all incident neutron energies. Previous work [6] has shown the importance of both the time-dependent and quantum-mechanical aspects of the theory to correctly reproduce the width of observed mass distributions through the spreading of the collective wave packet. In more phenomenological approaches (e.g., [16]) the effect of this quantum spreading is sometimes mimicked by coupling a quantum harmonic oscillator to a heat bath at finite temperature.…”

“…After an extensive analysis of TDGCM calculations of fragment distributions using the Q 20 and Q 30 coordinates, we were led to the conclusion that these coordinates, although very useful in describing the qualitative features of fission observables (see, e.g., [6,17]), are not ideal near, at, or beyond scission. We discovered that, no matter what reasonable prescription we used to relate the Q 20 and Q 30 coordinates to a fragment mass number, some fragment masses were severely under-represented in the yield distribution.…”

Event-by-event evaluation of the prompt fission neutron spectrum from239Pu(n,f)

“…Nevertheless, a quantitative theory of fission is not yet available. While there has been considerable progress in the last few years, both in liquid-drop model-type calculations [1,2] and in microscopic treatments [3][4][5], these treatments primarily address "cold" fission, induced by thermal neutrons, and cannot yet describe "hot fission", induced by more energetic neutrons. In order to perform new evaluations of observables important for applications over the full relevant energy range, it is therefore necessary to rely on a considerable degree of phenomenological modeling.…”