Neutron correlations and clustering in neutron-rich nuclear systems

Abstract

In this paper, we will briefly review the recent progress on neutron correlations and clustering in neutron-rich nuclei from quasi-free scattering experiments. The quasi-free ($p$, $pn$) reaction was measured for Borromean nuclei ${}^{11}$Li, ${}^{14}$Be, and ${}^{17}$B. A surprisingly small $s$-wave component was found for ${}^{17}$B, revealing a weak neutron halo in ${}^{17}$B, and the comparative study of the three nuclei shows the surface localization of dineutron correlation and its universality in Borromean nuclei. The two-neutron emission of ${}^{16}$Be was also studied, finding strong dineutron correlation in ${}^{16}$Be(g.s.) but weak correlation in ${}^{16}$Be($2^{+}$). Two missing-mass measurements using ${}^4$He(${}^8$He, ${}^8$Be) and ${}^8$He($p$, $p\alpha$) reactions provided evidence for the ${}^{4}n$ resonance, but the ${}^{3}n$ resonance was not supported by the recent experiment employing the $t(t{,}^3$He)${}^{3}n$ charge-exchange reaction. The quasi-free $(p,p\alpha )$ reaction has been extended to unstable nuclei, and the recent experiment unravels the $\alpha$-$2n$-$\alpha$ molecule-like cluster structure of ${}^{10}$Be(g.s.).

Comments: This article is part of a review collection from the Symposium 'Direct reactions and spectroscopy with hydrogen targets: past 10 years at the RIBF and future prospects'