Proton Radii of 12-17B Define a Thick Neutron Surface in 17B

The first determination of radii of point proton distribution (proton radii) of B12-17 from charge-changing cross sections (sigma(CC)) measurements at the FRS, GSI, Darmstadt is reported. The proton radii are deduced from a finite-range Glauber model analysis of the sCC. The radii show an increase from B-13 to B-17 and are consistent with predictions from the antisymmetrized molecular dynamics model for the neutron-rich nuclei. The measurements show the existence of a thick neutron surface with neutron-proton radius difference of 0.51(0.11) fm in B-17.