Natural decay chain

A decay chain refers to a sequence of radioactive decays. Three primordial decay chains have been observed in nature, with starting nuclides ²³²Th (T_½ = 1.405·10¹⁰ y), ²³⁸U (T_½ = 4.468·10⁹ y) and ²³⁵U (T_½ = 4.07·10⁸ y):

• thorium series
• uranium series
• actinium series

In addition to these chains, there is a fourth one:

• neptunium series

Due to the relatively short half-life of the starting nuclide ²³⁷Np (T_½ = 1.14·10⁶ y), this chain is already extinct in nature.

Related concepts

• cosmic radiation
• cosmogenic radionuclide
• nuclear fission (natural reactor)
• nucleosynthesis
• primordial radionuclide