Decoupling of valence neutrons from the core in 16C

The neutron and proton excitations in C-16 nucleus have been investigated by use of the Coulomb-nuclear interference method applied to the Pb-208 + C-16 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, M-n and M-p, have been determined from the Coulomb and matter deformation-length parameters obtained by distorted wave calculations. The M-p 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 M-n/M-p ratio has an unexpectedly large value of 7.6 +/- 1.7. These results suggest that the 2(1)(+) state in C-16 is a nearly pure valence neutron excitation. (C) 2004 Published by Elsevier B.V.