Rare isotope facilities have given access to the neutron-rich side of the nuclear
landscape. In this Seminar General, recent experimental results from the Radioactive Isotope Beam Facility of RIKEN, Japan, regarding the most neutron-rich accessible nuclear systems will be presented, in particular the recent observation of a correlated system of four free neutrons  and the evolution of the neutron shell structure in neutron-rich medium mass nuclei [2,3].
 M. Duer et al., Nature 606, 678 (2022).
 R. Taniuchi et al., Nature 569, 53 (2019).
 M. Enciu et al., Phys. Rev. Lett. 129, 262501 (2022).