Map of atomic nuclides. Three-dimensional representation of the known atomic nuclides, or isotopes. Atomic mass increases toward the bottom of the frame, proton number increases toward lower right and neutron number increases toward lower left. The white 'backbone' columns represent the stable nuclei found in nature, with hydrogen at the top and uranium near the centre. The orange 'terrace' represents radioactive isotopes which undergo beta decay, and the red those which undergo alpha decay. Yellow peaks near the bottom denote isotopes which undergo spontaneous fission. The small red column at the bottom of the frame represents the artificial element 112.