Naturally occurringzirconium (₄₀Zr) is composed of four stableisotopes (of which onemay in the future be found radioactive), and one very long-livedradioisotope (⁹⁶Zr), aprimordial nuclide that decays viadouble beta decay with an observedhalf-life of 2.0×10¹⁹ years;^[4] it can also undergo singlebeta decay, which is not yet observed, but the theoretically predicted value of t_1/2 is 2.4×10²⁰ years.^[5] The second most stable radioisotope is⁹³Zr, which has a half-life of 1.53 million years. Thirty other radioisotopes have been observed. All have half-lives less than a day except for⁹⁵Zr (64.02 days),⁸⁸Zr (83.4 days), and⁸⁹Zr (78.41 hours). The primary decay mode iselectron capture for isotopes lighter than⁹²Zr, and the primary mode for heavier isotopes is beta decay.

⁸⁸Zr is aradioisotope ofzirconium with a half-life of 83.4 days. In January 2019, this isotope was discovered to have aneutron capturecross section of approximately 861,000 barns; this is several orders of magnitude greater than predicted, and greater than that of any other nuclide exceptxenon-135.^[10]

⁸⁹Zr is a radioisotope of zirconium with ahalf-life of 78.41 hours. It is produced by proton irradiation of natural yttrium-89. Its most prominent gamma photon has an energy of 909 keV.

Zirconium-89 is employed in specialized diagnostic applications usingpositron emission tomography^[11] imaging, for example, with zirconium-89 labeled antibodies (immuno-PET).^[12] For a decay table, seeMaria Vosjan."Zirconium-89 (⁸⁹Zr)". Cyclotron.nl.

⁹³Zr is aradioisotope ofzirconium with ahalf-life of 1.53 million years, decaying through emission of a low-energybeta particle. 73% of decays populate anexcited state ofniobium-93, which decays with a half-life of 14 years and a low-energygamma ray to the stable ground state of⁹³Nb, while the remaining 27% of decays directly populate the ground state.^[7] It is one of only 7long-lived fission products. The low specific activity and low energy of its radiations limit the radioactive hazards of this isotope.

Nuclear fission produces it at a fission yield of 6.3% (thermal neutron fission of²³⁵U), on a par with the other most abundant fission products. Nuclear reactors usually contain large amounts of zirconium asfuel rodcladding (seezircaloy), and neutron irradiation of⁹²Zr also produces some⁹³Zr, though this is limited by⁹²Zr's lowneutron capturecross section of 0.22barns. Indeed, one of the primary reasons for using zirconium in fuel rod cladding is its low cross section.

⁹³Zr also has a lowneutron capturecross section of 0.7 barns.^[14][15] Most fission zirconium consists of other isotopes; the other isotope with a significant neutron absorption cross section is⁹¹Zr with a cross section of 1.24 barns.⁹³Zr is a less attractive candidate for disposal bynuclear transmutation than are⁹⁹Tc and¹²⁹I. Mobility in soil is relatively low, so thatgeological disposal may be an adequate solution. Alternatively, if the effect on theneutron economy of⁹³
Zr's higher cross section is deemed acceptable, irradiated cladding and fission product Zirconium (which are mixed together in most currentnuclear reprocessing methods) could be used to form new zircalloy cladding. Once the cladding is inside the reactor, the relatively low level radioactivity can be tolerated, but transport and manufacturing might require special precautions.

• 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
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003)."Atomic weights of the elements. Review 2000 (IUPAC Technical Report)".Pure and Applied Chemistry.75 (6):683–800.doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006)."Atomic weights of the elements 2005 (IUPAC Technical Report)".Pure and Applied Chemistry.78 (11):2051–2066.doi:10.1351/pac200678112051.
• "News & Notices: Standard Atomic Weights Revised".International Union of Pure and Applied Chemistry. 19 October 2005.
• 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.