Beta-decay properties of neutron-rich Zr isotopes … properties of neutron-rich Zr isotopes studied...
1
- xxiv - RIKEN Accel. Prog. Rep. 47 (2014) HIGHLIGHTS OF THE YEAR Beta-decay properties of neutron-rich Zr isotopes studied by the Skyrme energy-density functional method † K. Yoshida *1 The study of unstable nuclei has been a major sub- ject in nuclear physics for a couple of decades. The collective mode of excitation emerging in the response of the nucleus to an external field is a manifestation of the interaction among nucleons. Thus, the spin- isospin channel of the interaction and the spin-isospin part of the energy-density functional (EDF), which is crucial for understanding and predicting the proper- ties of unstable nuclei and asymmetric nuclear matter, have been studied in much detail, especially through Gamow-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 be- cause β-decay half-lives set a time scale for the rapid- neutron-capture process (r-process), and hence deter- mine the production of heavy elements in the uni- verse. The r-process path is far away from the sta- bility line, and involves neutron-rich nuclei. They are weakly bound and many of them are expected to be de- formed according to the systematic Skyrme-EDF cal- culation 1) . 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 RIBF 2) . The ground-state properties such as deformation and superfluidity in neutron-rich Zr isotopes up to the drip line have been studied by employing the Skyrme- Hartree-Fock-Bogoliubov (HFB) method, and it has been predicted that Zr isotopes around A = 110 are well deformed in the ground states 3) . To investigate the GT mode of excitation and β- decay properties in the deformed neutron-rich Zr iso- topes, we construct a new framework of the deformed HFB + proton-neutron QRPA employing the Skyrme EDF self-consistently in both the static and dynamic levels. Furthermore, the HFB equations are solved in real space for a proper description of the pairing cor- relations in weakly bound systems and coupling to the continuum states. The T = 0 pairing interaction is effective for the GT excitation in systems where the ground states have the T = 1 pairing condensates. In the neutron-rich Zr iso- topes under investigation, we find that the T = 0 pair- ing interaction enhances the low-lying GT strengths. The low-lying GT strength distribution strongly af- fects the β-decay rate. Thus, we can clearly see the † Condensed from the article in Prog. Theor. Exp. Phys. (2013) 113D02 *1 Graduate School of Science and Technology, Niigata Univer- sity Fig. 1. Experimental and theoretical β-decay half-lives of the Zr isotopes, calculated by employing the SLy4 EDF combined with and without the T = 0 pairing interac- tion. effect of T = 0 pairing in the β-decay life time. We can calculate the β-decay half-life T 1/2 with Fermi’s golden rule by using the GT strength distributions mi- croscopically obtained in the self-consistent pnQRPA framework. Figure 1 shows the β-decay half-lives of the Zr iso- topes calculated with the SLy4 EDF combined with and without the T = 0 pairing interaction. We see that the attractive T = 0 pairing interaction substantially shortens the β-decay half-lives. β-decay rates depend primarily on the Q β value, the residual interactions in both the p-h and p-p channels, and the shell struc- tures. The framework developed here self-consistently treats these key ingredients on the same footing. Once the strength of the T = 0 pairing interaction is deter- mined so as to reproduce the observed β-decay half-life of 100 Zr, our calculation scheme well produces the iso- topic dependence of the half-lives up to 110 Zr as was recently observed at RIBF. References 1) 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).
Transcript of Beta-decay properties of neutron-rich Zr isotopes … properties of neutron-rich Zr isotopes studied...
- xxiv -
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 sub-ject in nuclear physics for a couple of decades. Thecollective mode of excitation emerging in the responseof the nucleus to an external field is a manifestationof the interaction among nucleons. Thus, the spin-isospin channel of the interaction and the spin-isospinpart of the energy-density functional (EDF), which iscrucial for understanding and predicting the proper-ties 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 extensivelyinvestigated experimentally and theoretically not onlybecause of interest in the nuclear structure but also be-cause β-decay half-lives set a time scale for the rapid-neutron-capture process (r-process), and hence deter-mine the production of heavy elements in the uni-verse. The r-process path is far away from the sta-bility line, and involves neutron-rich nuclei. They areweakly bound and many of them are expected to be de-formed according to the systematic Skyrme-EDF cal-culation1).
Recently, β-decay half-lives of neutron-rich Kr to Tcisotopes with A ≃ 110 located on the boundary ofthe 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 Skyrme-Hartree-Fock-Bogoliubov (HFB) method, and it hasbeen predicted that Zr isotopes around A = 110 arewell deformed in the ground states3).
To investigate the GT mode of excitation and β-decay properties in the deformed neutron-rich Zr iso-topes, we construct a new framework of the deformedHFB + proton-neutron QRPA employing the SkyrmeEDF self-consistently in both the static and dynamiclevels. Furthermore, the HFB equations are solved inreal space for a proper description of the pairing cor-relations 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 iso-topes under investigation, we find that the T = 0 pair-ing interaction enhances the low-lying GT strengths.The low-lying GT strength distribution strongly af-fects the β-decay rate. Thus, we can clearly see the
† Condensed from the article in Prog. Theor. Exp. Phys.(2013) 113D02
∗1 Graduate School of Science and Technology, Niigata Univer-sity
Fig. 1. Experimental and theoretical β-decay half-lives of
the Zr isotopes, calculated by employing the SLy4 EDF
combined with and without the T = 0 pairing interac-
tion.
effect of T = 0 pairing in the β-decay life time. Wecan calculate the β-decay half-life T1/2 with Fermi’sgolden rule by using the GT strength distributions mi-croscopically obtained in the self-consistent pnQRPAframework.
Figure 1 shows the β-decay half-lives of the Zr iso-topes 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 dependprimarily on the Qβ value, the residual interactions inboth the p-h and p-p channels, and the shell struc-tures. The framework developed here self-consistentlytreats these key ingredients on the same footing. Oncethe strength of the T = 0 pairing interaction is deter-mined so as to reproduce the observed β-decay half-lifeof 100Zr, our calculation scheme well produces the iso-topic dependence of the half-lives up to 110Zr 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).
1
