Isotopes of tantalum

Natural tantalum (₇₃Ta) consists of two stable isotopes: ¹⁸¹Ta (99.988%) and 180m
Ta
(0.012%).

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 114.43 days, ¹⁸³Ta with a half-life of 5.1 days, and ¹⁷⁷Ta 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 ^180mTa) is ^178m1Ta with a half-life of 2.36 hours.

Tantalum has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of ¹⁸¹Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope 182
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.^[2]

Tantalum-180m

The nuclide 180m
Ta
(m denotes a metastable state) has sufficient energy to decay in three ways: isomeric transition to the ground state of 180
Ta
, beta decay to 180
W
, and electron capture to 180
Hf
. However, no radioactivity from any decay mode of this nuclear isomer has ever been observed. Only a lower limit on its half-life of over 10¹⁵ years has been set, by observation. 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.^[3]

The very unusual nature of ^180mTa is that the ground state of this isotope is less stable than the isomer. The same property is exhibited in americium-242m (^242mAm). 180
Ta
has a half-life of only 8 hours. 180m
Ta
is the only naturally occurring nuclear isomer (excluding radiogenic and cosmogenic short-living nuclides). It is also the rarest primordial nuclide in the Universe observed for any element that has any stable isotopes.

As of October 3, 2016 the half life of ^180mTa is calculated to be least 45x10¹⁵ (45 million billion) years.^[4][5]

List of isotopes

1. ↑ Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
2. ↑ Bold for stable isotopes, bold italics for nearly-stable isotopes (half-life longer than the age of the universe)
3. ↑ 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 2.0×10¹⁶ years
4. ↑ Believed to undergo α decay to ¹⁷⁷Lu

Notes

• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

References

1. ↑ Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure Appl. Chem. 88 (3): 265–91. doi:10.1515/pac-2015-0305. 
2. ↑ D. T. Win; M. Al Masum (2003). "Weapons of Mass Destruction" (PDF). Assumption University Journal of Technology. 6 (4): 199–219. 
3. ↑ Quantum mechanics for engineers Leon van Dommelen, Florida State University
4. ↑ Conover, Emily (2016-10-03). "Rarest nucleus reluctant to decay". Retrieved 2016-10-05. 
5. ↑ Lehnert, Björn; Hult, Mikael; Lutter, Guillaume; Zuber, Kai (2016-09-13). "Search for the decay of nature's rarest isotope ^180mTa". arXiv:1609.03725  [nucl-ex]. 
6. ↑ "Universal Nuclide Chart". nucleonica. (Registration required (help)). 

• Isotope masses from:
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. Archived from the original (PDF) on 2008-09-23. 
• Isotopic compositions and standard atomic masses from:
  • J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683. 
  • M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary. 
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. Archived from the original (PDF) on 2008-09-23. 
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.  Check date values in: |access-date= (help)
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.