Neutron Skin of Na Isotopes Studied via Their Interaction Cross Sections

The interaction cross sections $({\ensuremath{\sigma}}_{I})$ of ${}^{A}\mathrm{Na}$ isotopes $(A\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}20--23,25--32)$ on a carbon target have been measured at $950A\mathrm{MeV}$. The effective root-mean-square matter radii of these isotopes were deduced from ${\ensuremath{\sigma}}_{I}$ by a Glauber-type calculation. By combining the isotope-shift data with the present data the radii of neutrons have been compared with those of protons for the first time along a chain of stable and unstable isotopes. A monotonic increase in the neutron skin thickness has been observed as the neutron number increases in Na isotopes.