High-Momentum Correlated Nucleons, Tensor Blocking, and Nuclear Shell Structure

Studies of light neutron-rich nuclei revealed many new phenomena in nuclear structures and reactions. One of the most important recent discoveries is the change of magic numbers. Traditional magic numbers (2, 8, 20, 28, 50, 128) have been understood by the spin-orbit coupling in the mean-field potential and they provide the base of nuclear shell model. Recently, however, it was found that some of those magic numbers (N=8, 20) disappear in neutron-rich nuclei. On the other hand, new magic numbers (N=6, 14, 16, 32 and 34) emerge in neutron-rich nuclei. In the present paper, it is shown that tensor correlations give notable effects to such new structures. In nuclei a large amount of binding energy is gained by high-momentum correlated pairs of nucleons due to the tensor interaction. Such tensor correlations strongly depend on the configuration space available for exciting the 2p-2h states. When additional neutrons occupy a new orbital, the previously available 2p-2h configurations may be blocked, resulting in a sudden loss of binding energy otherwise gained by the 2p-2h excitations. Such tensor blocking effects enlarge the energy gaps at all the observed new magic numbers.