Abstract
The abundance peak around the mass region of neutron-rich lanthanides (Z~60, N~100) in the solar system isotopic abundance is of high interest as neutron-rich nuclei around this region are not expected to exhibit shell closure. Theoretical calculations propose that the lanthanide abundance originates from deformed sub-shell gap at N=104 which causes a pileup effect similar to closed shell nuclei during freeze-out. The existence of such a sub-shell gap can be identified via systematic two-neutron separation energies which require precise mass measurements of neutron-rich lanthanides. Key lanthanides of proton number, Z=60~68 and neutron number, N=100~108 will be produced with high statistics at the Radioactive Isotope Beam Factory (RIBF) in the Institute of Physical and Chemical Research (RIKEN). Using a multi-reflection time-of-flight mass spectrograph (MRTOF-MS), masses of the produced isotopes will be measured with an uncertainty of less than 100keV.
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