There are also 35 known artificial radioisotopes, the longest-lived of which are 179Ta with a half-life of 1.82 years, 182Ta with a half-life of 114.74 days, 183Ta with a half-life of 5.1 days, and 177Ta with a half-life of 56.46 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 180mTa) is 182m2Ta with a half-life of 15.8 minutes. 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 tantalum, irradiated by the intense high-energy neutron flux of the weapon, would be transmuted into the radioactive isotope 182 Ta, producing about 1.12MeV of gamma radiation per decay and significantly increasing the radioactivity of the weapon's fallout for months. Such a weapon is not known to have ever been built, tested, or used.[4]
↑ ()– Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
↑ #– Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
1 2 3 #– Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
↑ Bold italics symbol as daughter– Daughter product is nearly stable.
↑ Bold symbol as daughter– Daughter product is stable.
↑ () spin value– Indicates spin with weak assignment arguments.
1 2 3 4 5 Order of ground state and isomer is uncertain.
↑ Only known observationally stable nuclear isomer, believed to decay by isomeric transition to 180Ta, β− decay to 180W, or electron capture to 180Hf with a half-life over 2.9×1017 years;[6] also theorized to undergo α decay to 176Lu
The nuclide 180m 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 (210mBi) and americium-242m (242mAm), among other nuclides), it is exceptional in that it is observationally stable: no decay has ever been observed. In contrast, the ground state nuclide 180 Ta has a half-life of only 8 hours.
180m Ta has sufficient energy to decay in three ways: isomeric transition to the ground state of 180 Ta, beta decay to 180 W, or electron capture to 180 Hf. However, no radioactivity from any of these theoretically possible decay modes has ever been observed. As of 2023, the half-life of 180mTa is calculated from experimental observation to be at least 2.9×1017 (290 quadrillion) years.[6][8][9] The very slow decay of 180m 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.[10] Similar suppression of gamma or beta decay occurs for 210mBi, a rather short-lived alpha emitter.[11]
Because of this stability, 180m 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 kBT = 26keV (i.e. a temperature of 300 million kelvin), the nuclear isomers are expected to be fully thermalized, meaning that 180Ta is equilibrated between spin states and its overall half-life is predicted to be 11 hours.[12]
↑ 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.
1 2 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 180mTa". Phys. Rev. Lett. 131 (15) 152501. arXiv:2306.01965. doi:10.1103/PhysRevLett.131.152501.
↑ Chen, J. L.; Watanabe, H.; Walker, P. M.; etal. (2025). "Direct observation of β and γ decay from a high-spin long-lived isomer in 187Ta". Physical Review C. 111 (014304). arXiv:2501.02848. doi:10.1103/PhysRevC.111.014304.
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