Speaker
Description
The rapid neutron-capture process (r-process) is considered responsible for the production of approximately half of the elements heavier than iron in the universe. However, theoretical predictions of r-process abundance patterns still suffer from large uncertainties because experimental nuclear data for neutron-rich nuclei, including atomic masses, $\beta$-decay half-lives, and neutron-capture rates, remain scarce. In particular, the formation mechanism of the rare-earth abundance peak around mass number A ~ 165 has not yet been fully understood, and several mechanisms have been proposed depending on the astrophysical environment. Experimental data for neutron-rich lanthanide nuclei are essential for understanding the formation mechanism of the rare-earth peak.
Among the relevant nuclear properties, atomic masses play a particularly important role because they determine neutron separation energies and reaction Q-values, which strongly affect neutron-capture and $\beta$-decay processes. Even a mass variation of several hundred keV can significantly alter the calculated reaction rates and resulting abundance distributions. Precise mass measurements in the neutron-rich lanthanide region are therefore required to reduce the nuclear-physics uncertainties in r-process calculations.
In this study, we performed precision mass measurements of neutron-rich lanthanide isotopes produced in multinucleon transfer reactions using a $^{136}$Xe beam and a natural Er target at the KEK Isotope Separation System (KISS). The reaction products were collected and transported to a multi-reflection time-of-flight mass spectrograph (MRTOF-MS) for mass determination. In this presentation, we will report the experimental details and the results of the mass measurements.
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