β-delayed neutron emission probabilities of neutron-rich Zr to Pd isotopes and their impact on the nuclide abundance left-wing of the second r-process peak

New observational data on the r-process-enhanced metal-poor stars [1] have recently suggested a different source that consistently produces several light r-process elements from Se to Te, distinct from the mechanisms responsible for the heavier elements. These findings also call for new comparisons between nucleosynthesis models and observations for elements around the second r-process peak. However, such comparisons are obstructed by nuclear physics uncertainties, including the β decay properties of neutron-rich progenitors. To address these uncertainties to some extent, β-delayed neutron emission probabilities (P_1n and P_2n values) of ^106-112Zr, ^108-115Nb, ^110-118Mo, ^113-121Tc, ^117-123Ru, ^121-125Rh, and ^124-126Pd isotopes have been measured at the RIBF facility of the RIKEN Nishina Center. The experimental setup combines the silicon detector WAS3ABi with the YSO segmented scintillator surrounded by the BRIKEN ³He counters array [2]. In this talk, we will present the experimental details, the preliminary results in comparison with theoretical β-decay models, and discuss the impacts on the nucleosynthesis calculations of final r-process abundance pattern in this mass region.

[1] I. U. Roederer et al., Astrophys. J. 936, 84 (2022).

[2] A. Tolosa-Delgado et al., Nucl. Instrum. Methods Phys. Res., Sect. A 925, 133 (2019).