Nuclear-Matter Sizes in the Tin Isotopic Sequence

Differential cross sections and polarizations have been measured for 39.6-MeV protons elastically scattered from ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{122}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$. These data were analyzed with the optical model of Greenlees, Pyle, and Tang to extract nuclear-matter rms radii. These radii are significantly greater than the corresponding proton radii, and indicate that the neutrons added between successive even isotopes are added to the surface of the neutron distribution, with the exception of the isotope pair ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$-${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, in which case an anomaly occurs which suggests a structural rearrangement.