Speaker
Description
Understanding the origin of the heavy elements is a major goal of nuclear astrophysics. The rapid neutron-capture (r-) process is responsible for the production of approximately half of the elements heavier than iron, including the actinides uranium and thorium. One of the characteristic features of the resulting abundance distribution is the rare-earth peak around mass number A$\approx$160. The formation mechanism of this peak remains incompletely understood and is believed to be associated with the combined effects of maximum nuclear deformation and $\beta$-decay properties of neutron-rich nuclei in the rare-earth region.
The A$\sim$160 nuclei occupy a strongly deformed region of the nuclear chart. Among them, Nd isotopes ($Z=60$) are predicted to exhibit some of the largest ground-state deformations, as inferred from the systematics of first excited $2^+$ states in even-even nuclei. They therefore provide an important testing ground for investigating the role of deformation in the formation of the rare-earth peak. Experimental information on these neutron-rich nuclei remains limited owing to their distance from stability, although recent developments in radioactive ion-beam facilities have significantly expanded access to this region.
In this work, β–γ decay spectroscopy of $^{156}$Pr was performed to populate excited states in its daughter nucleus $^{156}$Nd. The experiment was carried out at the Radioactive Isotope Beam Factory (RIBF), RIKEN, where neutron-rich rare-earth isotopes were produced via in-flight fission of a 345 MeV/nucleon $^{238}$U beam incident on a Be target. Reaction products were separated and identified using the BigRIPS separator. Ion implantation and $\beta$-particle detection were achieved with the WAS3ABi active stopper, while $\gamma$ rays were detected using the EURICA germanium detector array.
The first $\beta$–$\gamma$ spectroscopy results for $^{156}$Pr will be presented. These measurements provide new information on the structure of $^{156}$Nd and contribute to understanding the role of nuclear deformation in the formation of the rare-earth peak.
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