Islands of stability
The stability of a nucleus depends critically on the number of protons and neutrons it contains, which can be clearly seen on a chart of the nuclides. The half-lives of nuclei are represented by different colours: black squares denote stable elements that are present in the crust of the Earth, while dark blue represents the "sea of instability" where nuclei live for less than 10-6 s. Nuclei shown in red live longer than those shown in green. In classical nuclear theory, the nucleus tends to become less stable as the number of protons and neutrons is increased. However, the microscopic shell model predicts that nuclei can live much longer if they contain certain "magic" numbers of protons and neutrons, giving rise to two "islands of stability" around N = 162 and 184. The yellow lines correspond to closed nuclear shells, next to which are indicated the magic proton and neutron numbers. The synthesis of new heavy elements followed by their sequential alpha decay - such as those with atomic number Z = 112 and 116 (white squares) - allows us to approach these islands of stability.