Systematics of isovector and isoscalar giant quadrupole resonances in normal and superfluid spherical nuclei

Abstract

The isoscalar (IS) and isovector (IV) quadrupole responses of nuclei are systematically investigated using the time-dependent Skyrme Energy Density Functional including pairing in the BCS approximation. Using two different Skyrme functionals, Sly4 and SkM*, respectively 263 and 304 nuclei have been found to be spherical along the nuclear charts. The time-dependent evolution of these nuclei has been systematically performed giving access to their quadrupole responses. It is shown that the mean-energy of the collective high energy state globally reproduces the experimental IS and IV collective energy but fails to reproduce their lifetimes. It is found that the mean collective energy depends rather significantly on the functional used in the mean-field channel. Pairing by competing with parity effects can slightly affect the collective response around magic numbers and induces a reduction of the collective energy compared to the average trend. Low-lying states, that can only be considered if pairing is included, are investigated. While the approach provides a fair estimate of the low lying state energy, it strongly underestimates the transition rate B(E2). Finally, the possibility to access to the density dependence of the symmetry energy through parallel measurements of both the IS-and IV-GQR is discussed.

Multipole excitations in hot nuclei within the finite temperature quasiparticle random phase approximation framework

“…For instance, the first 2 + state is neutron dominated and takes contributions from neutron 3s 1/2 → 2d 3/2 (23.9%), 1g 7/2 → 2d 3/2 (18.4%), 1h 11/2 → 1h 11/2 (15.2%), 2d 3/2 → 2d 3/2 (15.0%), 1g 7/2 → 1g 7/2 (6.3%) and proton 1g 9/2 → 2d 5/2 (3.8%) excitations. These results are also in agreement with previous theoretical studies [49,61]. By increasing temperature, the ISGQR centroid energy decreases while the strength increases.…”

“…It has been known that pairing correlations play a crucial role in the isoscalar quadrupole response in nuclei. Especially, the low-energy region is rather sensitive to the pairing effects [61]. The main reason for these changes in the isoscalar quadrupole response is the disappearance of the pairing correlations after the critical temperature.…”

Multipole modes of excitation in triaxially deformed superfluid nuclei

“…The axially deformed QRPA calculations with the modern Skyrme, Gogny, and covariant EDFs have recently become available [19][20][21][22][23], and the 3D RPA calculations without pairing were achieved [24][25][26][27]. However, currently, an efficient framework to solve the self-consistent QRPA with modern EDFs applicable to triaxial shapes is still missing, although there are some related studies using the real-time method [28][29][30][31][32].…”

Dynamical effects in fusion with exotic nuclei

“…Both quantities can be obtained from TDHF calculations of a single nucleus [62]. This method has been widely applied to study giant-resonances [65-67, 74, 79, 80], but more rarely to low-lying vibrations [46,72,74]. Although TDHF calculations can be used to study non-linear vibrations [81,82], the extraction of the transition strength relies on the linear regime, in which case it is equivalent to the random phase approximation (RPA).…”

“…These occupation numbers are kept constant during the dynamics, that is, we used the so-called frozen occupation number approximation [65]. A more sophisticated approach would imply a BCS [74] treatment to allow the occupation numbers n i to evolve in time. Unlike in fission in which dynamical pairing correlations play an important role [63,75,76], they have been shown to barely affect fusion [53] and are neglected in the present work.…”