Speaker
Description
Quasi-free scattering (QFS) reactions in inverse kinematics have emerged as a powerful tool to probe the microscopic structure of exotic nuclei. Using a thick liquid hydrogen target and the SAMURAI spectrometer at RIBF, a series of (p,2p) and (p,pn) measurements have been performed. Owing to the Fourier relationship between momentum and spatial distributions, the root-mean-square (rms) radii of valence nucleon orbitals can be extracted from measured momentum distributions following one-nucleon removal within the DWIA framework. In particular, the analysis of the $^{52}$Ca(p,pn)$^{51}$Ca reaction revealed an extended p$_{3/2}$ neutron orbital, which was suggested to be responsible for the unexpectedly large charge radii observed in neutron-rich Ca isotopes while preserving the double-magic character of $^{52}$Ca. Building on this approach, we extend this method to study neutron-halo systems, in which weakly bound valence neutrons exhibit spatially extended distributions. The Borromean nucleus $^{11}$Li, with the valence neutrons dominantly occupying the p and s orbitals, represents a prototypical two-neutron halo system. In contrast, $^{17}$B exhibits a surprisingly small s-wave component despite long being considered as a two-neutron halo nucleus. These observations were interpreted as challenging the conventional view that dominant s- or p-wave occupancy is a prerequisite for halo formation. In this talk, we present results on the extracted rms radii of valence neutron orbitals in $^{11}$Li and $^{17}$B using measured momentum distributions following the (p,pn) reactions. The results may provide new insights into the underlying mechanisms of halo formation.