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β-Delayed One and Two Neutron Emission Probabilities Southeast of 132Sn and the Odd-Even Systematics in r-Process Nuclide Abundances

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Physical Review Letters
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The β-delayed one- and two-neutron emission probabilities (P1n and P2n) of 20 neutron-rich nuclei with N≥82 have been measured at the RIBF facility of the RIKEN Nishina Center. P1n of 130,131Ag, 133,134Cd, 135,136In, and 138,139Sn were determined for the first time, and stringent upper limits were placed on P2n for nearly all cases. β-delayed two-neutron emission (β2n) was unambiguously identified in 133Cd and 135,136In, and their P2n were measured. Weak β2n was also detected from 137,138Sn. Our results highlight the effect of the N=82 and Z=50 shell closures on β-delayed neutron emission probability and provide stringent benchmarks for newly developed macroscopic-microscopic and self-consistent global models with the inclusion of a statistical treatment of neutron and γ emission. The impact of our measurements on r-process nucleosynthesis was studied in a neutron star merger scenario. Our P1n and P2n have a direct impact on the odd-even staggering of the final abundance, improving the agreement between calculated and observed Solar System abundances. The odd isotope fraction of Ba in r-process-enhanced (r−II) stars is also better reproduced using our new data.