Interplay of quasiparticle-vibration coupling and pairing correlations on β-decay half-lives

Y.F Niu,Z.M Niu,G Colò,E Vigezzi

doi:10.1016/j.physletb.2018.02.061

Abstract

The nuclear β-decay half-lives of Ni and Sn isotopes, around the closed shell nuclei 78Ni and 132Sn, are investigated by computing the distribution of the Gamow–Teller strength using the Quasiparticle Random Phase Approximation (QRPA) with quasiparticle-vibration coupling (QPVC), based on ground-state properties obtained by Hartree–Fock–Bogoliubov (HFB) calculations. We employ the effective interaction SkM⁎ and a zero-range effective pairing force. The half-lives are strongly reduced by including the QPVC. We study in detail the effects of isovector (IV) and isoscalar (IS) pairing. Increasing the IV strength tends to increase the lifetime for nuclei in the proximity of, but lighter than, the closed-shell ones in QRPA calculations, while the effect is significantly reduced by taking into account the QPVC. On the contrary, the IS pairing mainly plays a role for nuclei after the shell closure. Increasing its strength decreases the half-lives, and the effect at QRPA and QRPA+QPVC level is comparable. The effect of IS pairing is particularly pronounced in the case of the Sn isotopes, where it turns out to be instrumental to obtain good agreement with experimental data.

Highlights

The nuclear β-decay is an important weak-interaction process, which provides information on spin and isospin properties of the nuclear effective interaction, and sets the time scale of the rapid neutron-capture process (r-process), and determines the production of heavy elements in the universe [1,2,3]
We have calculated the half-lives of a chain of Ni and Sn isotopes around the closed shell nuclei 78Ni and 132Sn, in the framework of the self-consistent Quasiparticle Random Phase Approximation (QRPA)+quasiparticle-vibration coupling (QPVC) model based on Skyrme density functional SkM∗, which has been shown to lead to a good agreement with experiment for half-lives of magic nuclei [44] and GT transitions of both magic [42] and superfluid nuclei [45]
We have investigated in detail the effects of IV pairing and IS pairing, both at QRPA and QRPA+QPVC level

Summary

Introduction

The nuclear β-decay is an important weak-interaction process, which provides information on spin and isospin properties of the nuclear effective interaction, and sets the time scale of the rapid neutron-capture process (r-process), and determines the production of heavy elements in the universe [1,2,3]. An effective way to account for (most of) the observed spreading widths is to take into account the coupling of single-nucleon states to the collective lowlying (mainly surface) nuclear vibrations or phonons (that is, to include 1p–1h–1 phonon configurations in the model space) [39] We call this model RPA plus PVC, and we note that self-consistent versions of such a model have been realized based on both relativistic and nonrelativistic energy functionals. The self-consistent QRPA with quasiparticlevibration coupling (QRPA+QPVC) model, based either on Skyrme EDFs [45] or on relativistic EDFs [46], was developed and used to study the GT transitions in superfluid nuclei This new development opens up the possibility to explore the β-decay half-lives for a whole isotopic chain. Further independent confirmations of this finding would be very valuable

Formalism

Results and discussions

Isovector pairing

The role of isoscalar pairing

Conclusions