RIKEN Accel. Prog. Rep. 47 (2014)

HIGHLIGHTS OF THE YEARRIKEN Accel. Prog. Rep. 00 (0)Beta-decay properties of neutron-rich Zr isotopes studied by theSkyrme energy-density functional method†
K. Yoshida∗1
The study of unstable nuclei has been a major subject in nuclear physics for a couple of decades. The
collective mode of excitation emerging in the responseof the nucleus to an external ﬁeld is a manifestationof the interaction among nucleons. Thus, the spinisospin channel of the interaction and the spin-isospin
part of the energy-density functional (EDF), which is
crucial for understanding and predicting the properties of unstable nuclei and asymmetric nuclear matter,
have been studied in much detail, especially throughGamow-Teller (GT) strength distributions.
The GT strength distribution has been extensively
investigated experimentally and theoretically not only
because of interest in the nuclear structure but also because β-decay half-lives set a time scale for the rapidneutron-capture process (r-process), and hence determine the production of heavy elements in the universe. The r-process path is far away from the stability line, and involves neutron-rich nuclei. They are
weakly bound and many of them are expected to be deformed according to the systematic Skyrme-EDF calculation1) .
Recently, β-decay half-lives of neutron-rich Kr to Tc
isotopes with A ≃ 110 located on the boundary of
the r-process path were newly measured at RIBF2) .
The ground-state properties such as deformation andsuperﬂuidity in neutron-rich Zr isotopes up to thedrip line have been studied by employing the SkyrmeHartree-Fock-Bogoliubov (HFB) method, and it hasbeen predicted that Zr isotopes around A = 110 are
well deformed in the ground states3) .
To investigate the GT mode of excitation and βdecay properties in the deformed neutron-rich Zr isotopes, we construct a new framework of the deformed
HFB + proton-neutron QRPA employing the Skyrme
EDF self-consistently in both the static and dynamiclevels. Furthermore, the HFB equations are solved inreal space for a proper description of the pairing correlations in weakly bound systems and coupling to thecontinuum states.
The T = 0 pairing interaction is eﬀective for the GTexcitation in systems where the ground states have theT = 1 pairing condensates. In the neutron-rich Zr isotopes under investigation, we ﬁnd that the T = 0 pairing interaction enhances the low-lying GT strengths.
The low-lying GT strength distribution strongly affects the β-decay rate. Thus, we can clearly see the†∗1

Condensed from the article in Prog. Theor. Exp. Phys.
(2013) 113D02
Graduate School of Science and Technology, Niigata UniversityFig. 1. Experimental and theoretical β-decay half-lives ofthe Zr isotopes, calculated by employing the SLy4 EDF
combined with and without the T = 0 pairing interaction.

eﬀect of T = 0 pairing in the β-decay life time. We
can calculate the β-decay half-life T1/2 with Fermi’s
golden rule by using the GT strength distributions microscopically obtained in the self-consistent pnQRPA
framework.
Figure 1 shows the β-decay half-lives of the Zr isotopes calculated with the SLy4 EDF combined withand without the T = 0 pairing interaction. We see thatthe attractive T = 0 pairing interaction substantiallyshortens the β-decay half-lives. β-decay rates depend
primarily on the Qβ value, the residual interactions inboth the p-h and p-p channels, and the shell structures. The framework developed here self-consistently
treats these key ingredients on the same footing. Oncethe strength of the T = 0 pairing interaction is determined so as to reproduce the observed β-decay half-lifeof 100 Zr, our calculation scheme well produces the isotopic dependence of the half-lives up to 110 Zr as wasrecently observed at RIBF.
References1) M. V. Stoitsov et al.: Phys. Rev. C 68, 054312 (2003).
2) S. Nishimura et al.: Phys. Rev. Lett. 106, 052502(2011).
3) A. Blazkiewicz et al.: Phys. Rev. C 71, 054321 (2005).

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