Protons and neutrons in an atomic nucleus form distinct shells that relate to increasing energy levels, in a manner similar to that of electrons orbiting in an atom. Significant energy gaps exist between shells that are completely filled at ‘magic’ numbers of protons or neutrons (2, 8, 20, 28, 50, 82 or 126). However, in unstable nuclei, magic numbers are known to evolve when a large imbalance of protons and neutrons exists. Experiments on the neutron-rich calcium nucleus 54Ca (composed of 20 protons and 34 neutrons) provide the first direct evidence that 34 is a new magic number for neutrons. This magic number represents the onset of a significant subshell closure in isotopes far from stability, David Steppenbeck and co-workers explain.
The results probe one of the fundamental properties of the atomic nucleus and enrich our knowledge of the structures of exotic nuclei in systems far from stability.
David Steppenbeck (University of Tokyo, Japan)
Tel: +81 484644191; E-mail: [email protected]