Speaker
Byul Moon
Description
In astrophysical environments, the beta($\beta$)-decay of unstable nuclei plays a crucial role in generating the final isotopic abundances along with rapid neutron-capture reactions (r-processes). The $\beta$-decay strengths are largely influenced by the so-called Gamow-Teller (G-T) interaction that is closely related to the spin-isospin interaction. This spin-isospin excitation is one of important ingredient for modeling the nuclear shell structure. Consequently, the role played by the G-T transition provides plenty of information on nuclear structure and nucleosynthesis. The G-T strength has been mainly constrained by the transformation between a proton and a neutron in the high-angular momentum orbital-spin partners such as; $\pi f_{7/2}$-$\nu f_{7/2}$, $\pi g_{9/2}$-$\nu g_{9/2}$, and $\pi h_{11/2}$-$\nu h_{11/2}$. However, in extreme neutron-rich environments, it can be controlled by the interplay between a neutron in the upper orbital and a proton in the lower orbital among a spin-orbital doublets, for instance, $\pi h_{11/2}$-$\nu h_{9/2}$.
Investigating of the neutron-rich nuclei beyond $^{132}$Sn has attracted much attention because they are expected to reveal changes of size, diffuseness, and shell closures and, on the other side, to give information on nucleosynthesis along the r-process paths. However, it is a challenging task to determine decay rates and life times for the nuclei in this region. Here we present for the first time the $\beta$-decay of $^{140}$Te ($Z=52$) to odd-odd $^{140}$I ($Z=53$). The parent nuclide $^{140}$Te was produced through the in-flight fission of $^{238}$U beam with the energy of 345 MeV per nucleon on a $^{9}$Be target at the Radioactive Ion Beam Factory (RIBF), RIKEN. By using a $\beta$-delayed $\gamma$-ray spectroscopy, a decay scheme of $^{140}$I has been established. Three levels fed strongly from the ground 0$^{+}$ state of the mother nucleus $^{140}$Te have been assigned as a 1$^{+}$ state based on the log$ft$ values. These 1$^{+}$ states can be interpreted as being associated with the $\pi h_{11/2}$$\nu h_{9/2}$ configuration formed by the G-T transition between a neutron in the $h_{9/2}$ orbital and a proton in the $h_{11/2}$ orbital. Systematic features of level structures and G-T transitions are discussed within the framework of the spherical shell model and deformed shell model descriptions.
