Isotopes of technetium

Isotopes of technetium (43Tc)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
95mTc synth 61.96 d β+ 95Mo
IT 95Tc
96Tc synth 4.28 d β+ 96Mo
97Tc synth 4.21×106 y ε 97Mo
97mTc synth 91.1 d IT 97Tc
ε 97Mo
98Tc synth 4.2×106 y β− 98Ru
99Tc trace 2.111×105 y β− 99Ru
99mTc synth 6.01 h IT 99Tc
β− 99Ru

Technetium (43Tc) is one of the two elements with Z < 83 that have no stable isotopes; the other such element is promethium.[2] It is primarily artificial, with only trace quantities existing in nature produced by spontaneous fission (there are an estimated 2.5×10−13 grams of 99Tc per gram of pitchblende)[3] or neutron capture by molybdenum. The first isotopes to be synthesized were 97Tc and 99Tc[disputed – discuss] in 1936, the first artificial element to be produced. The most stable radioisotopes are 97Tc (half-life of 4.21 million years), 98Tc (half-life: 4.2 million years), and 99Tc (half-life: 211,100 years).[4][5]

Thirty-three other radioisotopes have been characterized with atomic masses ranging from 85Tc to 120Tc.[6] Most of these have half-lives that are less than an hour; the exceptions are 93Tc (half-life: 2.75 hours), 94Tc (half-life: 4.883 hours), 95Tc (half-life: 20 hours), and 96Tc (half-life: 4.28 days).[7]

Technetium also has numerous meta states. 97mTc is the most stable, with a half-life of 91.0 days (0.097 MeV).[4] This is followed by 95mTc (half-life: 61 days, 0.038 MeV) and 99mTc (half-life: 6.04 hours, 0.143 MeV). 99mTc only emits gamma rays, subsequently decaying to 99Tc.[7]

For isotopes lighter than 98Tc, the primary decay mode is electron capture to isotopes of molybdenum. For the heavier isotopes, the primary mode is beta emission to isotopes of ruthenium, with the exception that 100Tc can decay both by beta emission and electron capture.[7][8]

Technetium-99m is the hallmark technetium isotope employed in the nuclear medicine industry. Its low-energy isomeric transition, which yields a gamma-ray at ~140.5 keV, is ideal for imaging using Single Photon Emission Computed Tomography (SPECT). Several technetium isotopes, such as 94mTc, 95gTc, and 96gTc, which are produced via (p,n) reactions using a cyclotron on molybdenum targets, have also been identified as potential Positron Emission Tomography (PET) agents.[9][10][11] Technetium-101 has been produced using a D-D fusion-based neutron generator from the 100Mo(n,γ)101Mo reaction on natural molybdenum and subsequent beta-minus decay of 101Mo to 101Tc. Despite its shorter half-life (i.e., 14.22 min), 101Tc exhibits unique decay characteristics suitable for radioisotope diagnostic or therapeutic procedures, where it has been proposed that its implementation, as a supplement for dual-isotopic imaging or replacement for 99mTc, could be performed by on-site production and dispensing at the point of patient care.[12]

Technetium-99 is the most common and most readily available isotope, as it is a major fission product from fission of actinides like uranium and plutonium with a fission product yield of 6% or more, and in fact the most significant long-lived fission product. Lighter isotopes of technetium are almost never produced in fission because the initial fission products normally have a higher neutron/proton ratio than is stable for their mass range, and therefore undergo beta decay until reaching the ultimate product. Beta decay of fission products of mass 95–98 stops at the stable isotopes of molybdenum of those masses and does not reach technetium. For mass 100 and greater, the technetium isotopes of those masses are very short-lived and quickly beta decay to isotopes of ruthenium. Therefore, the technetium in spent nuclear fuel is practically all 99Tc. In the presence of fast neutrons a small amount of 98
Tc will be produced by (n,2n) "knockout" reactions. If nuclear transmutation of fission-derived Technetium or Technetium waste from medical applications is desired, fast neutrons are therefore not desirable as the long lived 98
Tc increases rather than reducing the longevity of the radioactivity in the material.

One gram of 99Tc produces 6.2×108 disintegrations a second (that is, 0.62 GBq/g).[13]

Technetium has no stable or nearly stable isotopes, and thus a standard atomic weight cannot be given.

  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. ^ "Atomic weights of the elements 2011 (IUPAC Technical Report)" (PDF). IUPAC. p. 1059(13). Retrieved August 11, 2014. – Elements marked with a * have no stable isotope: 43, 61, and 83 and up.
  3. ^ Icenhower, J.P.; Martin, W.J.; Qafoku, N.P.; Zachara, J.M. (2008). The Geochemistry of Technetium: A Summary of the Behavior of an Artificial Element in the Natural Environment (Report). Pacific Northwest National Laboratory: U.S. Department of Energy. p. 2.1.
  4. ^ a b "Livechart - Table of Nuclides - Nuclear structure and decay data". www-nds.iaea.org. Retrieved 2017-11-18.
  5. ^ "Nubase 2016". NDS IAEA. 2017. Retrieved 18 November 2017.
  6. ^ National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  7. ^ a b c "Technetium". EnvironmentalChemistry.com.
  8. ^ 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.
  9. ^ Bigott, H. M.; Mccarthy, D. W.; Wüst, F. R.; Dahlheimer, J. L.; Piwnica-Worms, D. R.; Welch, M. J. (2001). "Production, processing and uses of 94mTc". Journal of Labelled Compounds and Radiopharmaceuticals. 44 (S1): S119–S121. doi:10.1002/jlcr.2580440141. ISSN 1099-1344.
  10. ^ Morley, Thomas; Benard, Francois; Schaffer, Paul; Buckley, Kenneth; Hoehr, Cornelia; Gagnon, Katherine; McQuarrie, Steve; Kovacs, Michael; Ruth, Thomas (2011-05-01). "Simple, rapid production of Tc-94m". Journal of Nuclear Medicine. 52 (supplement 1): 290. ISSN 0161-5505.
  11. ^ Hayakawa, Takehito; Hatsukawa, Yuichi; Tanimori, Toru (January 2018). "95g Tc and 96g Tc as alternatives to medical radioisotope 99m Tc". Heliyon. 4 (1): e00497. Bibcode:2018Heliy...400497H. doi:10.1016/j.heliyon.2017.e00497. ISSN 2405-8440. PMC 5766687. PMID 29349358.
  12. ^ Mausolf, Edward J.; Johnstone, Erik V.; Mayordomo, Natalia; Williams, David L.; Guan, Eugene Yao Z.; Gary, Charles K. (September 2021). "Fusion-Based Neutron Generator Production of Tc-99m and Tc-101: A Prospective Avenue to Technetium Theranostics". Pharmaceuticals. 14 (9): 875. doi:10.3390/ph14090875. PMC 8467155. PMID 34577575.
  13. ^ The Encyclopedia of the Chemical Elements, p. 693, "Toxicology", paragraph 2