Decoupling of valence neutrons from the core in 16C

The neutron and proton excitations in 16C nucleus have been investigated by use of the Coulomb-nuclear interference method applied to the 208Pb+16C inelastic scattering. Angular distribution of the 16C nuclei in the inelastic channel populating the first 2+ state has been measured. The neutron and proton transition matrix elements, Mn and Mp, have been determined from the “Coulomb” and “matter” deformation-length parameters obtained by distorted wave calculations. The Mp or its corresponding B(E2;2+1→0+) value was found to be extremely small: 0.28±0.06 Weisskopf units consistent with a recent lifetime measurement. Furthermore, the extracted Mn/Mp ratio has an unexpectedly large value of 7.6±1.7. These results suggest that the 2+1 state in 16C is a nearly pure valence neutron excitation.