Figure 1: Three-dimensional representation of the theoretical island of stability in nuclear physics. The half-life of nuclides is plotted as a function of proton ($Z$) and neutron ($N$) number. The continent of stable elements ends at the lead–bismuth cape, and a region of relative stability appears around the isotopes of thorium and uranium ($Z=90,92$). In the region of the heaviest (superheavy) elements, theory predicts an “island of stability” around proton number 114 or 120 and neutron number 184.