Abstract: The origin of chemical elements in the Universe is a fundamental question in astrophysics. While elements up to iron are primarily produced within stars, the main mechanism for the formation of heavier nuclei is the neutron capture. The rate of neutron capture relative to beta decay determines whether this process is slow (s-process) or rapid (r-process). Nearly half of the elements heavier than iron are produced by the r-process, which occurs in explosive events such as supernovae or neutron star mergers. The solar system r-process residual abundances show two peaks at A∼130 and A∼195. 

Between these peaks lies the Rare-Earth Peak (REP), a distinct but small peak at mass number A∼160 that arises from the freeze-out during the final stages of neutron exposure. According to sensitivity studies, half-lives (T1/2) and β-delayed neutron emission probabilities (Pxn) of neutron-rich nuclei, in the mass region A∼160 are critical for the formation of the REP [1,2]. The BRIKEN collaboration [3] conducted an extensive measurement program of β-decay properties of nuclei involved in the r-process at the Radioactive Isotope Beam Factory (RIBF) in the RIKEN Nishina Center, Japan. The BRIKEN-REP experiment measured nuclei from Ba to Nd (A∼160), belonging to the region that is the most influential to the REP formation [4]. In this talk, we will present new experimental measurements of T1/2 and Pxn for REP neutron-rich nuclei. Additionally, we will discuss recent theoretical calculations and how they compare with the experimental data.

References:
[1] M. R. Mumpower et al., Phys. Rev. C 85, 045801 (2012).

[2] A. Arcones and G. Martinez Pinedo, Phys. Rev. C 83, 045809 (2011).

[3] J.L. Tain et. al., Acta Physica Polonica B 49(03), 417 − 428 (2018).

[4] A. Tarifeño-Saldivia et al., RIKEN Accel. Prog. Rep. 54, 27. (2021).