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Natural tantalum (₇₃Ta) consists of two stable isotopes: Ta (99.988%) and
Ta
(0.012%).

There are also 35 known artificial radioisotopes, the longest-lived of which are Ta with a half-life of 1.82 years, Ta with a half-life of 114.43 days, Ta with a half-life of 5.1 days, and Ta with a half-life of 56.56 hours. All other isotopes have half-lives under a day, most under an hour. There are also numerous isomers, the most stable of which (other than Ta) is Ta with a half-life of 2.36 hours. All isotopes and nuclear isomers of tantalum are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.

Tantalum has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope
Ta
with a half-life of 114.43 days and produce approximately 1.12 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several months. Such a weapon is not known to have ever been built, tested, or used. While the conversion factor from absorbed dose (measured in Grays) to effective dose (measured in Sievert) for gamma rays is 1 while it is 50 for alpha radiation (i.e., a gamma dose of 1 Gray is equivalent to 1 Sievert whereas an alpha dose of 1 Gray is equivalent to 50 Sievert), gamma rays are only attenuated by shielding, not stopped. As such, alpha particles require incorporation to have an effect while gamma rays can have an effect via mere proximity. In military terms, this allows a gamma ray weapon to deny an area to either side as long as the dose is high enough, whereas radioactive contamination by alpha emitters which do not release significant amounts of gamma rays can be counteracted by ensuring the material is not incorporated.

List of isotopes

1. Ta – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. ^ # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
5. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   p:	Proton emission

6. Bold italics symbol as daughter – Daughter product is nearly stable.
7. Bold symbol as daughter – Daughter product is stable.
8. ( ) spin value – Indicates spin with weak assignment arguments.
9. ^ Order of ground state and isomer is uncertain.
10. Only known observationally stable nuclear isomer, believed to decay by isomeric transition to Ta, β decay to W, or electron capture to Hf with a half-life over 2.9×10 years; also theorized to undergo α decay to Lu
11. One of the few (observationally) stable odd-odd nuclei
12. Believed to undergo α decay to Lu

Tantalum-180m

The nuclide
Ta
(m denotes a metastable state) is one of a very few nuclear isomers which are more stable than their ground states. Although it is not unique in this regard (this property is shared by bismuth-210m (Bi) and americium-242m (Am), among other nuclides), it is exceptional in that it is observationally stable: no decay has ever been observed. In contrast, the ground state nuclide
Ta
has a half-life of only 8 hours.

Ta
has sufficient energy to decay in three ways: isomeric transition to the ground state of
Ta
, beta decay to
W
, or electron capture to
Hf
. However, no radioactivity from any of these theoretically possible decay modes has ever been observed. As of 2023, the half-life of Ta is calculated from experimental observation to be at least 2.9×10 (290 quadrillion) years. The very slow decay of
Ta
is attributed to its high spin (9 units) and the low spin of lower-lying states. Gamma or beta decay would require many units of angular momentum to be removed in a single step, so that the process would be very slow.

Because of this stability,
Ta
is a primordial nuclide, the only naturally occurring nuclear isomer (excluding short-lived radiogenic and cosmogenic nuclides). It is also the rarest primordial nuclide in the Universe observed for any element which has any stable isotopes. In an s-process stellar environment with a thermal energy k_BT = 26 keV (i.e. a temperature of 300 million kelvin), the nuclear isomers are expected to be fully thermalized, meaning that Ta rapidly transitions between spin states and its overall half-life is predicted to be 11 hours.

It is one of only five stable nuclides to have both an odd number of protons and an odd number of neutrons, the other four stable odd-odd nuclides being H, Li, B and N.

References

1. ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
2. "Standard Atomic Weights: Tantalum". CIAAW. 2005.
3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
4. D. T. Win; M. Al Masum (2003). "Weapons of Mass Destruction" (PDF). Assumption University Journal of Technology. 6 (4): 199–219.
5. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
6. ^ Arnquist, I. J.; Avignone III, F. T.; Barabash, A. S.; Barton, C. J.; Bhimani, K. H.; Blalock, E.; Bos, B.; Busch, M.; Buuck, M.; Caldwell, T. S.; Christofferson, C. D.; Chu, P.-H.; Clark, M. L.; Cuesta, C.; Detwiler, J. A.; Efremenko, Yu.; Ejiri, H.; Elliott, S. R.; Giovanetti, G. K.; Goett, J.; Green, M. P.; Gruszko, J.; Guinn, I. S.; Guiseppe, V. E.; Haufe, C. R.; Henning, R.; Aguilar, D. Hervas; Hoppe, E. W.; Hostiuc, A.; Kim, I.; Kouzes, R. T.; Lannen V., T. E.; Li, A.; López-Castaño, J. M.; Massarczyk, R.; Meijer, S. J.; Meijer, W.; Oli, T. K.; Paudel, L. S.; Pettus, W.; Poon, A. W. P.; Radford, D. C.; Reine, A. L.; Rielage, K.; Rouyer, A.; Ruof, N. W.; Schaper, D. C.; Schleich, S. J.; Smith-Gandy, T. A.; Tedeschi, D.; Thompson, J. D.; Varner, R. L.; Vasilyev, S.; Watkins, S. L.; Wilkerson, J. F.; Wiseman, C.; Xu, W.; Yu, C.-H. (13 October 2023). "Constraints on the Decay of Ta". Phys. Rev. Lett. 131 (15) 152501. arXiv:2306.01965. doi:10.1103/PhysRevLett.131.152501.
7. Conover, Emily (2016-10-03). "Rarest nucleus reluctant to decay". Science News. Retrieved 2016-10-05.
8. Lehnert, Björn; Hult, Mikael; Lutter, Guillaume; Zuber, Kai (2017). "Search for the decay of nature's rarest isotope Ta". Physical Review C. 95 (4) 044306. arXiv:1609.03725. Bibcode:2017PhRvC..95d4306L. doi:10.1103/PhysRevC.95.044306. S2CID 118497863.
9. Quantum mechanics for engineers Leon van Dommelen, Florida State University
10. P. Mohr; F. Kaeppeler; R. Gallino (2007). "Survival of Nature's Rarest Isotope Ta under Stellar Conditions". Phys. Rev. C. 75 012802. arXiv:astro-ph/0612427. doi:10.1103/PhysRevC.75.012802. S2CID 44724195.
11. Lide, David R., ed. (2002). Handbook of Chemistry & Physics (88th ed.). CRC. ISBN 978-0-8493-0486-6. OCLC 179976746. Archived from the original on 24 July 2017. Retrieved 2008-05-23.

• 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.

v t e Isotopes of the chemical elements
Group 1 2   3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Period Hydrogen and alkali metals Alkaline earth metals Pnicto­gens Chal­co­gens Halo­gens Noble gases ① Isotopes § ListH1 Isotopes § ListHe2 ② Isotopes § ListLi3 Isotopes § ListBe4 Isotopes § ListB5 Isotopes § ListC6 Isotopes § ListN7 Isotopes § ListO8 Isotopes § ListF9 Isotopes § ListNe10 ③ Isotopes § ListNa11 Isotopes § ListMg12 Isotopes § ListAl13 Isotopes § ListSi14 Isotopes § ListP15 Isotopes § ListS16 Isotopes § ListCl17 Isotopes § ListAr18 ④ Isotopes § ListK19 Isotopes § ListCa20 Isotopes § ListSc21 Isotopes § ListTi22 Isotopes § ListV23 Isotopes § ListCr24 Isotopes § ListMn25 Isotopes § ListFe26 Isotopes § ListCo27 Isotopes § ListNi28 Isotopes § ListCu29 Isotopes § ListZn30 Isotopes § ListGa31 Isotopes § ListGe32 Isotopes § ListAs33 Isotopes § ListSe34 Isotopes § ListBr35 Isotopes § ListKr36 ⑤ Isotopes § ListRb37 Isotopes § ListSr38 Isotopes § ListY39 Isotopes § ListZr40 Isotopes § ListNb41 Isotopes § ListMo42 Isotopes § ListTc43 Isotopes § ListRu44 Isotopes § ListRh45 Isotopes § ListPd46 Isotopes § ListAg47 Isotopes § ListCd48 Isotopes § ListIn49 Isotopes § ListSn50 Isotopes § ListSb51 Isotopes § ListTe52 Isotopes § ListI53 Isotopes § ListXe54 ⑥ Isotopes § ListCs55 Isotopes § ListBa56 Isotopes § ListLu71 Isotopes § ListHf72 Isotopes § ListTa73 Isotopes § ListW74 Isotopes § ListRe75 Isotopes § ListOs76 Isotopes § ListIr77 Isotopes § ListPt78 Isotopes § ListAu79 Isotopes § ListHg80 Isotopes § ListTl81 Isotopes § ListPb82 Isotopes § ListBi83 Isotopes § ListPo84 Isotopes § ListAt85 Isotopes § ListRn86 ⑦ Isotopes § ListFr87 Isotopes § ListRa88 Isotopes § ListLr103 Isotopes § ListRf104 Isotopes § ListDb105 Isotopes § ListSg106 Isotopes § ListBh107 Isotopes § ListHs108 Isotopes § ListMt109 Isotopes § ListDs110 Isotopes § ListRg111 Isotopes § ListCn112 Isotopes § ListNh113 Isotopes § ListFl114 Isotopes § ListMc115 Isotopes § ListLv116 Isotopes § ListTs117 Isotopes § ListOg118 ⑧ Isotopes § ListUue119 Isotopes § ListUbn120 Isotopes § ListLa57 Isotopes § ListCe58 Isotopes § ListPr59 Isotopes § ListNd60 Isotopes § ListPm61 Isotopes § ListSm62 Isotopes § ListEu63 Isotopes § ListGd64 Isotopes § ListTb65 Isotopes § ListDy66 Isotopes § ListHo67 Isotopes § ListEr68 Isotopes § ListTm69 Isotopes § ListYb70   Isotopes § ListAc89 Isotopes § ListTh90 Isotopes § ListPa91 Isotopes § ListU92 Isotopes § ListNp93 Isotopes § ListPu94 Isotopes § ListAm95 Isotopes § ListCm96 Isotopes § ListBk97 Isotopes § ListCf98 Isotopes § ListEs99 Isotopes § ListFm100 Isotopes § ListMd101 Isotopes § ListNo102
Table of nuclides Categories: Isotopes Tables of nuclides Metastable isotopes Isotopes by element

• Isotopes of tantalum
• Tantalum
• Lists of isotopes by element