Chart of nuclides, formed by plotting atomic number Z as a function of neutron number N for known radioactive isotopes (grey). Stable isotopes are shown by black squares. Horizontal and vertical lines indicate magic Z and N, respectively (see text) and the stars indicate the doubly magic nuclides ⁷⁸Ni and ¹³²Sn. The red line shows a possible r-process path and the colored lines correspond to neutron drip lines calculated by different mass models. Inset (left) is a surface plot defined by the mass excess, derived from measured binding energies. Beta-decaying nuclides are in orange and blue, alpha-emitters in yellow, proton-emitters in red and neutron emitters in purple. Stable nuclides, again in black, are seen to form the so-called valley of stability into which all nuclides with higher mass excess decay.