Radius of ⁹C from the Asymptotic Normalization Coefficient

The asymptotic normalization coefficient (ANC) of ⁹C = ⁸B+p deduced from ⁸Li(d,p)⁹Li reaction is used to obtain the root-mean-square (rms) radius of the loosely bound proton in the ⁹C ground state. We obtain (r²)^1/2 = 3.61fm for the valence proton, which is significantly larger than the matter radius of ⁹C. The probability of the valence proton outside the matter radius of ⁹C is greater than 60%. The present work supports the conclusion that ⁹C has a proton halo structure.