Speaker
Description
Around half of the nuclei 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 elemental solar system abundances, located at $A\sim 130$ and $A\sim 195$, which are associated with the neutron shell closure during the $(n,\gamma)$ $\leftrightarrow$ $(\gamma ,n)$ equilibrium. In contrast, the rare-earth peak (REP) is a small - but clear - peak around mass $A=160$, which originates from the freeze-out during the late phases 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], launched in 2016 at the RIBF in the RIKEN Nishina Center, aims to measure $\beta$-decay properties for a large number of nuclei on the path of the r-process. Accordingly, $T_{1/2}$ and $P_{n}$-values for the most influential nuclei to the REP formation from Ba to Eu ($A\sim 160$) have been measured for the first time with BRIKEN. In this work, the details of the measurements of about 25 isotopes in the region from Ce to Nd will be discussed. The first experimental results will be presented.
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) (2018) 417–428.
[4] A. Tolosa-Delgado and et. al, NIM A 925 (2019) 133 – 147