The decrease of ground-state correlations from 12C to 14C

The (d,tau) reactions on 12C, 13C and 14C have been investigated with 52 MeV deuterons. Spectroscopic factors have been extracted from a DWBA analysis of the measured angular distributions. The derived proton occupation numbers show that the addition of 1psub(1/2) neutrons leads to a consolidation of the 1psub(3/2) proton shell closure: The number of protons in the 1psub(1/2) shell of the target wave function decreases from 0.7 in 12C to about 0.4 in 13C and 0.3 in 14C. This decrease is understood as the result of (i) a blocking of proton scattering into the 1psub(1/2) shell due to the presence of 1psub(1/2) neutrons or (ii) a decreasing deformation with increasing neutron number. (Auth.)