Isotopes of niobium

Naturally occurring niobium (Nb), element 41, is composed of one stable isotope (⁹³Nb). ⁹³Nb is the lightest nuclide theoretically susceptible to spontaneous fission, and although this has never been observed, it makes niobium theoretically the lightest element with no stable isotope. The first 40 elements (to zirconium) all have at least one stable nuclide which is susceptible in theory only to proton decay.

The most stable radioisotope is ⁹²Nb with a half-life of 34.7 million years. This nuclide is the longest-lived radionuclide of all elements that has not yet been detected in nature as a primordial isotope.^[1] (The nuclide with the next longest half-life, ²⁴⁴Pu with half-life 80 million years, has been detected, and is thus primordial).

The next longest-lived niobium nuclides are ⁹⁴Nb (half-life: 20,300 years), and ⁹¹Nb with a half-life of 680 years. There is also a meta state at 31 keV whose half-life is 16.13 years. Twenty three other radioisotopes have been characterized. Most of these have half-lives that are less than two hours except ⁹⁵Nb (35 days), ⁹⁶Nb (23.4 hours) and ⁹⁰Nb (14.6 hours). The primary decay mode before the stable ⁹³Nb is electron capture and the primary mode after is beta emission with some neutron emission occurring in ^104-110Nb.

Only ⁹⁵Nb (35 days) and ⁹⁷Nb (72 minutes) and heavier isotopes (half-lives in seconds) are fission products in significant quantity, as the other isotopes are shadowed by stable or very long-lived (⁹³Zr) isotopes of the preceding element zirconium from production via beta decay of neutron-rich fission fragments. ⁹⁵Nb is the decay product of ⁹⁵Zr (64 days), so disappearance of ⁹⁵Nb in used nuclear fuel is slower than would be expected from its own 35 day halflife alone. Tiny amounts of the other isotopes may be produced as direct fission products.

Niobium's standard atomic mass is 92.90638(2) u.

Table

1. ↑ Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
2. ↑ Bold for stable isotopes, bold italic for near-stable isotopes (half-life longer than the age of the universe)
3. ↑ Longest half-life of all non-primordial radionuclides
4. ↑ Theoretically capable of spontaneous fission, lightest nuclide so capable

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. ↑ There are many shorter-lived radioisotopes in nature, but they are all cosmogenic or radiogenic
2. ↑ http://www.nucleonica.net/unc.aspx

• Isotope masses from:
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (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:
  • J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and 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 and O. Bersillon (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 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. 
  • 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.