Speaker
Description
Around half of the elemental abundances heavier than iron are created via the rapid neutron capture process (r-process). For nuclear masses $A>100$, there are two main peaks in the r-process abundances, located at $A\sim 130$ and $A\sim 195$. These peaks are associated with neutron shell closures. In contrast, the rare-earth peak (REP) is a small - but clear - peak around mass $A=160$, appearing in late phases of the freeze-out after neutron exhaustion. The formation of the REP offers a unique probe for the study of the late-time conditions on the r-process site. According to theoretical models and sensitivity studies, half-lives $(T_{1/2})$ and beta-delayed neutron emission probabilities $(P_{n})$ of very neutron-rich nuclei for $55\le Z\le64$ are the most influential ones on the formation of the REP [1,2]. The BRIKEN project [3,4] has been in operation from 2016 up to 2021 at the Radioactive Isotope Beam Factory (RIBF) in the RIKEN Nishina Center, Japan. BRIKEN has performed an ambitious measurement program of beta-decay properties of nuclei on the path of the r-process. The overall expected outcome of the BRIKEN project is to report for the first time about 120 half-lives and 300 measurements of single and multiple beta-delayed neutron emitters. Moreover, the BRIKEN-REP experiment has recently measured $T_{1/2}$ and $P_n$-values of nuclei from Ba to Eu (A $\sim$ 160), belonging to the region which is the most influential to the REP formation [5,6]. In this contribution, we will discuss the status of the BRIKEN-REP experiment. The first experimental results of new $P_{1n}$-values and $T_{1/2}$ for nuclei in the neutron-rich region from La to Nd will be presented.
[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. Tolosa-Delgado et. al , NIM A 925, 133 - 147 (2019).
[5] G. Kiss et al , RIKEN Accel. Prog. Rep. 53, 33. (2020).
[6] A. Tarifeño-Saldivia et al , RIKEN Accel. Prog. Rep. 54, 27. (2021)
