Differential cross sections for p- ${}^6\mathrm{He}$ and p- ${}^8\mathrm{He}$ elastic scattering have been measured in inverse kinematics at small momentum transfers up to $|t|=0.05\mathrm{}(\mathrm{GeV}/c{)}^2$ and projectile energies of about 700 MeV/nucleon. Nuclear matter densities deduced from the data are consistent with the concept that ${}^6\mathrm{He}$ and ${}^8\mathrm{He}$ nuclei have an $\alpha$-like core and a significant neutron skin. The rms radii of the nuclear matter distributions were determined to be $R_m$ ${(}^6\mathrm{He})=2.30\mathrm{}\pm 0.07\mathrm{fm}$ and $R_m$ ${(}^8\mathrm{He})=2.45\mathrm{}\pm 0.07\mathrm{fm}$.

• Received 2 December 1996

DOI:https://doi.org/10.1103/PhysRevLett.78.2313