Gamow–Teller transitions of neutron-rich N = 82,81 nuclei by shell-model calculations

Noritaka Shimizu,Tomoaki Togashi,Yutaka Utsuno

doi:10.1093/ptep/ptab022

Noritaka Shimizu, Tomoaki Togashi + Show 1 more

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https://doi.org/10.1093/ptep/ptab022

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Abstract

Abstract $\beta$ -decay half-lives of neutron-rich nuclei around $N=82$ are key data to understand the $r$-process nucleosynthesis. We performed large-scale shell-model calculations in this region using a newly constructed shell-model Hamiltonian, and successfully described the low-lying spectra and half-lives of neutron-rich $N=82$ and $N=81$ isotones with $Z=42\text{--}49$ in a unified way. We found that their Gamow–Teller strength distributions have a peak in the low excitation energies, which significantly contributes to the half-lives. This peak, dominated by $\nu 0g_{7/2} \to \pi 0g_{9/2}$ transitions, is enhanced on the proton-deficient side because the Pauli-blocking effect caused by occupying the valence proton $0g_{9/2}$ orbit is weakened.

Highlights

The solar system abundances and their peak structures indicate that major origin of most elements heavier than iron is generated by the r-process nucleosynthesis [1]
In the region where the r-process path comes across the magic number N = 82, these nuclei form the waiting points of neutron captures in the r-process
The path comes along the N = 82 line in the chart bringing about the so-called second peak of the natural abundance formed by the astrophysical r-process nucleosynthesis

Summary

INTRODUCTION

The solar system abundances and their peak structures indicate that major origin of most elements heavier than iron is generated by the r-process nucleosynthesis [1]. The β-decay properties of the N = isotones and of the N = ones are necessary to determine the r-process path, motivating the study of those very neutron-rich nuclei from the viewpoint of nuclear structure physics. Β-delayed neutron-emission probabilities and low-lying level structure have been measured [11, 12] These data provide a stringent test for nuclear-structure models. The measured half-lives are well reproduced by the calculation, and we predict those for 125,126Ru, 124,125Tc and 124Mo. It is predicted that these nuclei have rather strong GT strengths in the low excitation energies due to the increasing number of proton holes in the g9/2 orbit, accelerating GT decay.

FRAMEWORK OF SHELL-MODEL CALCULATIONS

SEPARATION ENERGIES AND EXCITATION ENERGIES

SUMMARY