Speaker
Description
The rapid neutron-capture (r-) process produces heavy elements in the mass range $70\leq A\leq209$, including actinides such as uranium and thorium. A defining feature of this process is its characteristic abundance distribution. It possesses a small yet distinct enhancement around A$\approx$160, known as the rare-earth peak. The origin of this peak remains an open question and is thought to arise from the combined effects of maximum nuclear deformation and β-decay properties of neutron-rich rare-earth nuclei in the A$\sim$160 region. These nuclei lie in one of the deformed sectors of the nuclear chart. In particular, the systematics of the first excited $2^+$ states in even-even nuclei suggest that Nd ($Z=60$) isotopes exhibit among the largest ground-state deformations in this mass region. The experimental data for nuclei in the rare-earth region far from stability have been limited, but advances in radioactive-beam facilities have made their study accessible. In this work, we investigate the $\beta$-$\gamma$ spectroscopy of $^{156}$Pr ($Z=59$, $N=97$) to populate its daughter $^{156}$Nd ($Z=60$, $N=96$). Such studies are not only important for understanding the origin of the rare-earth peak but also provide valuable insight into nuclear structure and the evolution of nuclear deformation in this region.
The experiment was conducted at RIBF, RIKEN, using in-flight fission of a 345 MeV/nucleon $^{238}$U beam on a Be target to produce neutron-rich rare-earth isotopes. The isotopes were separated and identified using the BigRIPS separator. An active stopper, WAS3ABi, was used for ion- and $\beta$-detection, while an array of Ge detectors, EURICA, was used for $\gamma$-ray detection. This enabled us to perform the $\beta$-$\gamma$ spectroscopy.
In the presentation, first $\beta$-$\gamma$ decay spectroscopy results for $^{156}$Pr will be presented, providing nuclear structure information relevant to rare-earth peak formation.