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~130 and A~195, which are associated with the neutron shell closure during the (n,γ)→(γ,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 (T1/2) and beta-delayed neutron emission probabilities (Pn) of very neutron-rich nuclei for 55< Z<64 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, T1/2 and Pn-values for the most influential nuclei to the REP formation from Ba to Eu (A~160) have been measured for the first time with BRIKEN. In this work, the measurements of T1/2 and beta-delayed neutron branching probabilities (P1n) for several Pr and Nd isotopes in the mass region A~160 will be discussed. Preliminary experimental results on P1n-values will be presented for the first time.
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