  Absolute differential cross sections for elastic $p^7$Be and $p^8$B
small-angle scattering were measured in inverse kinematics at an energy of 0.7
GeV/u at GSI Darmstadt. The hydrogen-filled ionization chamber IKAR was used as
an active target to detect the recoil protons. The projectile tracking and
isotope identification were performed with multi-wire proportional chambers and
scintillation detectors. The measured cross sections were analysed using the
Glauber multiple-scattering theory. The root-mean-square (rms) nuclear matter
radii $R_{\rm m} = 2.42 (4)$ fm for $^7$Be and $R_{\rm m} = 2.58 (6)$ fm for
$^8$B were obtained. The radial density distribution deduced for $^8$B exhibits
a proton halo structure with the rms halo radius $R_{\rm h} = 4.24 (25)$ fm. A
comparison of the deduced experimental radii is displayed with existing
experimental and theoretical data.
