Lead (₈₂Pb) has fourobservationally stableisotopes:²⁰⁴Pb,²⁰⁶Pb,²⁰⁷Pb,²⁰⁸Pb. Lead-204 is entirely aprimordial nuclide and is not aradiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of threedecay chains: theuranium series (or radium series), theactinium series, and thethorium series, respectively; a fourth decay chain, theneptunium series, terminates with thethallium isotope²⁰⁵Tl. The three series terminating in lead represent the decay chain products of long-lived primordial²³⁸U,²³⁵U, and²³²Th. Each isotope also occurs, to some extent, as primordial isotopes that were made in supernovae, rather than radiogenically as daughter products. The fixed ratio of lead-204 to the primordial amounts of the other lead isotopes may be used as the baseline to estimate the extra amounts of radiogenic lead present in rocks as a result of decay from uranium and thorium. (Seelead–lead dating anduranium–lead dating.)

The longest-livedradioisotopes are²⁰⁵Pb with ahalf-life of 17.3 million years and²⁰²Pb with a half-life of 52,500 years. A shorter-lived naturally occurring radioisotope,²¹⁰Pb with a half-life of 22.2 years, is useful for studying thesedimentation chronology of environmental samples on time scales shorter than 100 years.^[5]

The relative abundances of the four stable isotopes are approximately 1.5%, 24%, 22%, and 52.5%, combining to give astandard atomic weight (abundance-weighted average of the stable isotopes) of 207.2(1). Lead is the element with the heaviest stable isotope,²⁰⁸Pb. (The more massive²⁰⁹Bi, long considered to be stable, actually has a half-life of 2.01×10¹⁹ years.)²⁰⁸Pb is also adoubly magic isotope, as it has 82protons and 126neutrons.^[6] It is the heaviest doubly magic nuclide known. A total of 43 lead isotopes are now known, including very unstable synthetic species.

The four primordial isotopes of lead are allobservationally stable, meaning that they are predicted to undergo radioactive decay but no decay has been observed yet. These four isotopes are predicted to undergoalpha decay and becomeisotopes of mercury which are themselves radioactive or observationally stable.

In its fully ionized state, thebeta decay of isotope²¹⁰Pb does not release a free electron; the generated electron is instead captured by the atom's empty orbitals.^[7]

²⁰⁶Pb is the final step in the decay chain of²³⁸U, the "radium series" or "uranium series". In a closed system, over time, a given mass of²³⁸U will decay in a sequence of steps culminating in²⁰⁶Pb. The production of intermediate products eventually reaches an equilibrium (though this takes a long time, as the half-life of²³⁴U is 245,500 years). Once this stabilized system is reached, the ratio of²³⁸U to²⁰⁶Pb will steadily decrease, while the ratios of the other intermediate products to each other remain constant.

Like most radioisotopes found in the radium series,²⁰⁶Pb was initially named as a variation of radium, specificallyradium G. It is the decay product of both²¹⁰Po (historically calledradium F) byalpha decay, and the much rarer²⁰⁶Tl (radium E^II) bybeta decay.

Lead-206 has been proposed for use infast breeder nuclear fission reactor coolant over the use of natural lead mixture (which also includes other stable lead isotopes) as a mechanism to improveneutron economy and greatly suppress unwanted production of highly radioactive byproducts.^[12]

²⁰⁴Pb is entirelyprimordial, and is thus useful for estimating the fraction of the other lead isotopes in a given sample that are also primordial, since the relative fractions of the various primordial lead isotopes is constant everywhere.^[13] Any excess lead-206, -207, and -208 is thus assumed to beradiogenic in origin,^[13] allowing various uranium and thorium dating schemes to be used to estimate the age of rocks (time since their formation) based on the relative abundance of lead-204 to other isotopes.²⁰⁷Pb is the end of theactinium series from²³⁵U.

²⁰⁸Pb is the end of thethorium series from²³²Th. While it only makes up approximately half of the composition of lead in most places on Earth, it can be found naturally enriched up to around 90% in thorium ores.^[14]208Pb is the heaviest known stable nuclide and also the heaviest knowndoubly magic nucleus, asZ = 82 andN = 126 correspond to closednuclear shells.^[15] As a consequence of this particularly stable configuration, its neutron capturecross section is very low (even lower than that ofdeuterium in the thermal spectrum), making it of interest forlead-cooled fast reactors.

In 2025 a published study suggested that the nucleus of²⁰⁸Pb is not perfectly spherical as previously believed.^[16]

²¹²Pb-containingradiopharmaceuticals have been trialed as therapeutic agents for the experimental cancer treatmenttargeted alpha-particle therapy.^[17]

• Meija, Juris; et al. (2016)."Atomic weights of the elements 2013 (IUPAC Technical Report)".Pure and Applied Chemistry.88 (3):265–291.doi:10.1515/pac-2015-0305.

Isotope masses from:

• Audi, Georges; Bersillon, Olivier; Blachot, Jean;Wapstra, Aaldert Hendrik (2003),"The NUBASE evaluation of nuclear and decay properties",Nuclear Physics A,729:3–128,Bibcode:2003NuPhA.729....3A,doi:10.1016/j.nuclphysa.2003.11.001

Half-life, spin, and isomer data selected from the following sources.

• Audi, Georges; Bersillon, Olivier; Blachot, Jean;Wapstra, Aaldert Hendrik (2003),"The NUBASE evaluation of nuclear and decay properties",Nuclear Physics A,729:3–128,Bibcode:2003NuPhA.729....3A,doi:10.1016/j.nuclphysa.2003.11.001
• National Nuclear Data Center."NuDat 2.x database".Brookhaven National Laboratory.
• Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.).CRC Handbook of Chemistry and Physics (85th ed.).Boca Raton, Florida:CRC Press.ISBN 978-0-8493-0485-9.

• Isotopes of lead
• Lead
• Lists of isotopes by element

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