Ponente
Abstract
The Rare Earth Peak (REP) is a small, but clearly distinctive, peak around mass A∼160 in the elemental solar system abundances created by the rapid neutron-capture process (r-process). In contrast to the r-process abundance peaks associated with neutron shell closures (e.g. A ∼ 130, 195), which are formed during the (n, γ) ↔ (γ, n) equilibrium, the REP is formed at late times after the neutron exhaustion. Thus, understanding of the REP formation offers a unique probe for the study of the late times environmental conditions in the r-process site. According to theoretical models, half-lives (T1/2) and beta-delayed neutron emission probabilities (Pn) play an important role on the formation of the REP.
The Beta-delayed neutrons at RIKEN project (BRIKEN), launched in 2016 at RIBF in the RIKEN Nishina Center, with an important contribution from Spanish groups, aims to measure the decay properties (mainly T1/2 and Pn) for a large number of isotopes on the path of the r-process by using the BRIKEN setup. The BRIKEN NP1612-RIBF148 experiment is focused on the measurement of the most relevant nuclei, the neutron-rich isotopes from Cs to Gd, linked to the REP formation. The last run of this experiment, achieved in 2018 with a setting centered on 165Pm, provided data for measurement of nuclei in the region from Ce to Eu. The status of this experiment is discussed. Preliminary results focused on Ce to Nd isotopes are presented.
