Uranserie

Uranserie, or the uranium decay series, refers to natural chains of radioactive decay that originate from long-lived isotopes of uranium and thorium and progress until a stable lead isotope is formed. In geology and geochemistry, three primary series are recognized: the uranium-238 series (the radium series), the uranium-235 series (the actinium series), and the thorium-232 series (the thorium series). Each series consists of a sequence of alpha and beta decays, with occasional short-lived gaseous intermediates such as radon.

The 238U series begins with uranium-238 and decays through a succession of radionuclides such as 234U, 226Ra, and 222Rn before ending at 206Pb. This is one of the main natural sources of radiogenic lead and underpins many uranium-lead dating applications. The half-lives of the isotopes span billions of years, reflecting the long time scales involved in the chain.

The 235U series starts at uranium-235 and proceeds through daughter nuclides including protactinium-231 and other intermediates before reaching 207Pb. Its shorter half-life relative to 238U means its activity is significant in different geological contexts and it also contributes to radiometric dating in combination with the 238U series.

The 232Th series begins with thorium-232 and progresses to 208Pb via a sequence of intermediates such as 228Ra, 228Th, 224Ra, and other short-lived nuclides. This series is important for understanding thorium-bearing minerals and the dating of certain rocks and soils.

Natural occurrence includes minerals like uraninite and thorite. The decay chains are exploited in geochronology, groundwater studies, and environmental health assessments, where radon gas from some decay steps can pose hazards.