Neutron Radius ofPb208from Sub-Coulomb Pickup

The ($d,t$) and ($p,d$) reactions on ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ have been studied at several energies below the Coulomb barrier. Relatively simple and parameter-free analysis yields the absolute normalization of the asymptotic tail for the neutron states near the Fermi surface. A wide range of Woods-Saxon potentials that match the binding energy and the asymptotic tail yield a rather unique value of the rms radius for the neutron excess, namely 5.99 ± 0.10 fm. This is very close to the radius deduced from Coulomb-energy differences.