SEASTAR project

The "Shell Evolution And Search for Two-plus energies At RIBF" (SEASTAR) project aims at a systematic search for new 2⁺ energies in the wide range of the neutron-rich nuclei accessible with the RIBF's presently available ⁷⁰Zn and ²³⁸U beam intensities. It covers the following physics interests:

• Neutron sub-shell at N = 34 below ⁵⁴Ca (⁵²Ar)
• Correlations in Ca isotopes beyond ⁵⁴Ca (⁵⁶Ca)
• Low-Z shore of the N = 40 “Island of Inversion” (^60,62Ti)
• Collectivity evolution beyond N = 40 (⁶⁶Cr, ⁷²Fe)
• Anticipated new doubly-magic nucleus ⁷⁸Ni
• Orbital migration beyond N = 50 (^82-84Zn, ^86,88Ge, ^90,92Se)
• Delineation of the rise in collectivity at N ∼ 60 (⁹⁴Se, ^98,100Kr)
• Evidence for a N = 70 sub-shell effect (¹¹⁰Zr)

The project will be performed using ⁷⁰Zn and ²³⁸U primary beams at 345 MeV/u in combination with BigRIPS, DALI2, MINOS, and ZeroDegree or SAMURAI, the latter two depending on the mass of nuclei to be studied. During the proposed measurements, also new isotopes can be discovered. In the case of fission fragments secondary beams, the EURICA setup can be used simultaneously at the final focus of F11 to systematically search for new isomeric states. For experiments with SAMURAI including NEBULA, invariant mass spectroscopy of unbound states can be simultaneously performed.