Global systematics of octupole excitations in even-even nuclei

Abstract

We present a computational methodology for a theory of the lowest octupole excitations applicable to all even-even nuclei beyond the lightest. The theory is the well-known generator-coordinate extension (GCM) of the Hartree-Fock-Bogoliubov self-consistent mean field theory (HFB). We use the discrete-basis Hill-Wheeler method (HW) to compute the wave functions with an interaction from the Gogny family of Hamiltonians. Comparing to the compiled experimental data on octupole excitations, we find that the performance of the theory depends on the deformation characteristics of the nucleus. For nondeformed nuclei, the theory reproduces the energies to about ±20 % apart from an overall scale factor of ≈ 1.6. The performance is somewhat poorer for (quadrupole) deformed nuclei, and for both together the dispersion of the scaled energies about the experimental values is about ±25 %. This compares favorably with the performance of similar theories of the quadrupole excitations. Nuclei having static octupole deformations in HFB form a special category. These nuclei have the smallest measured octupole excitation energies as well as the smallest predicted energies. However, in these cases the energies are seriously underpredicted by the theory.We find that a simple two-configuration approximation, the Minimization After Projection method,

Interplay between tensor force and deformation in even–even nuclei

“…The local minima of the energy functional is determined within the second order gradient method. Details of the method are presented in [37] and references therein.…”

How atomic nuclei cluster

“…A number of recent studies based on nuclear EDFs or the mean-field approach have analysed cluster structures in α-conjugate nuclei [15][16][17][18][19][20][21]. In Fig.…”

Improvements on the present theoretical understanding of octupole correlations

“…Excitation energies of negative parity states are predicted [4] to be systematically higher than experimental data. A hint on the origin of the discrepancies is the good agreement with experiment for the 3 − excitation energy of 208 Pb computed with RPA and the Gogny force [7].…”

“…In our survey of [4] the above method is implemented with the the three standard parametrization (D1S, D1N and D1M) of the Gogny force. The Gogny force has been chosen because of its reputation in describing many different phenomena all over the nuclear chart.…”

“…A sound theoretical description encompassing both regimes is provided by the generator coordinate method (GCM) with the octupole deformation as generating coordinate [3]. Recently, such kind of calculations [4] have been performed for a set of 818 even-even nuclei and several variants of the Gogny interaction. Results for the excitation energy of the lowest lying collective negative parity state and the E1 and E3 transition strengths to the ground state have been computed and compared to experimental data.…”