Halos and Multineutron Correlations in Light Neutron-Rich Nuclei

This review summarizes recent experimental progress in the structure and correlations of light neutron-rich nuclei. We first highlight achievements based on quasi-free scattering reactions in inverse kinematics at the Radioactive Isotope Beam Factory (RIBF), including investigations of the single-particle composition of halo systems—for example, revealing the minimal s-wave component in the “weak-halo” nucleus 17B—and the mapping of universal, surface-localized dineutron correlations in Borromean nuclei such as 11Li, 14Be and 17B. We then discuss recent advances in the study of multineutron correlations and cluster states, addressing both experimental challenges and major breakthroughs. These include the observation of a candidate 4n resonance, the absence of a resonant state in the 3n system, the characterization of direct two-neutron decay in 16Be, and evidence for a condensate-like α+n2+n2 cluster structure in the He8(02+) state. Finally, we discuss prospects for extending such investigations to heavier halo candidates and more complex multineutron systems, and outline the development of next-generation neutron detector arrays that will drive future progress in this field.