Isotopes_of_astatine

Isotopes of astatine

Isotopes of astatine

Nuclides with atomic number of 85 but with different mass numbers

Astatine (85At) has 41 known isotopes, all of which are radioactive; their mass numbers range from 188 to 229 (though 189At is undiscovered).[2] There are also 24 known metastable excited states. The longest-lived isotope is 210At, which has a half-life of 8.1 hours; the longest-lived isotope existing in naturally occurring decay chains is 219At with a half-life of 56 seconds.

Quick Facts Main isotopes, Decay ...

List of isotopes

More information Nuclide, Z ...
  1. [n 1]
    mAt – Excited nuclear isomer.
  2. [n 2]
    ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. [n 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. [n 4]
    Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
  5. [n 5]
    Bold italics symbol as daughter – Daughter product is nearly stable.
  6. [n 6]
    ( ) spin value – Indicates spin with weak assignment arguments.
  7. [n 7]
    # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  8. [n 8]
    Theoretically capable of β+ decay to 212Po or β− decay to 212Rn[5][1]
  9. [n 9]
    Intermediate decay product of 235U
  10. [N 10]
    Theoretically capable of electron capture to 216Po or β− decay to 216Rn[5][1]
  11. [N 11]
    Intermediate decay product of 237Np
  12. [N 12]
    Intermediate decay product of 238U

Alpha decay

More information Mass number, Massexcess ...

Astatine has 23 nuclear isomers (nuclei with one or more nucleons – protons or neutrons – in an excited state). A nuclear isomer may also be called a "meta-state"; this means the system has more internal energy than the "ground state" (the state with the lowest possible internal energy), making the former likely to decay into the latter. There may be more than one isomer for each isotope. The most stable of them is astatine-202m1,[lower-alpha 3] which has a half-life of about 3 minutes; this is longer than those of all ground states except those of isotopes 203–211 and 220. The least stable one is astatine-214m1; its half-life of 265 ns is shorter than those of all ground states except that of astatine-213.[5]

Alpha decay energy follows the same trend as for other heavy elements.[7] Lighter astatine isotopes have quite high energies of alpha decay, which become lower as the nuclei become heavier. However, astatine-211 has a significantly higher energy than the previous isotope; it has a nucleus with 126 neutrons, and 126 is a magic number (corresponding to a filled neutron shell). Despite having a similar half-life time as the previous isotope (8.1 hours for astatine-210 and 7.2 hours for astatine-211), the alpha decay probability is much higher for the latter: 41.8 percent versus just 0.18 percent.[5][lower-alpha 4] The two following isotopes release even more energy, with astatine-213 releasing the highest amount of energy of all astatine isotopes. For this reason, it is the shortest-lived astatine isotope.[7] Even though heavier astatine isotopes release less energy, no long-lived astatine isotope exists; this happens due to the increasing role of beta decay.[7] This decay mode is especially important for astatine: as early as 1950, it was postulated that the element has no beta-stable isotopes (i.e. ones that do not undergo beta decay at all),[8] though nuclear mass measurements reveal that 215At is in fact beta-stable, as it has the lowest mass of all isobars with A = 215.[9] A beta decay mode has been found for all other astatine isotopes except for 212At, 213At, 214At, 216At and 216mAt.[5][1] Among other isotopes: astatine-210 and the lighter isotopes decay by positron emission; astatine-217 and the heavier isotopes undergo beta decay; and astatine-211 decays by electron capture instead.[5] Astatine-212 and astatine-216 are expected to decay either way.

The most stable isotope of astatine is astatine-210, which has a half-life of about 8.1 hours. This isotope's primary decay mode is positron emission to the relatively long-lived alpha emitter, polonium-210. In total, only five isotopes of astatine have half-lives exceeding one hour: those between 207 and 211. The least stable ground state isotope is astatine-213, with a half-life of about 125 nanoseconds. It undergoes alpha decay to the extremely long-lived (in practice, stable) isotope bismuth-209.[5]

See also

  1. In the table, under the words "mass excess", the energy equivalents are given rather than the real mass excesses; "mass excess daughter" stands for the energy equivalent of the mass excess sum of the daughter of the isotope and the alpha particle; "alpha decay half-life" refers to the half-life if decay modes other than alpha are omitted.
  2. Since astatine-221 has not been shown to undergo alpha decay, the alpha decay energy is theoretical. The value for mass excess is calculated rather than measured.
  3. "m1" means that this state of the isotope is the next possible one above – energy greater than – the ground state. "m2" and similar designations refer to further higher energy states. The number may be dropped if there is only one well-established meta state, such as astatine-216m. Note that other designation techniques exist.
  4. This means that if decay modes other than alpha are omitted, then astatine-210 has an alpha half-life of 4,628.6 hours (128.9 days) and astatine-211 has one of 17.2 hours (0.9 days). Therefore, astatine-211 is less stable toward alpha decay than the lighter isotope, and is more likely to undergo alpha decay in the same time period.

References

  1. [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. [2]
    Kokkonen, Henna. "Decay properties of the new isotopes 188At and 190At" (PDF). University of Jyväskylä. Retrieved 8 June 2023.
  3. [3]
    Kettunen, H.; Enqvist, T.; Grahn, T.; Greenlees, P.T.; Jones, P.; Julin, R.; Juutinen, S.; Keenan, A.; Kuusiniemi, P.; Leino, M.; Leppänen, A.-P.; Nieminen, P.; Pakarinen, J.; Rahkila, P.; Uusitalo, J. (1 August 2003). "Alpha-decay studies of the new isotopes 191At and 193At" (PDF). The European Physical Journal A - Hadrons and Nuclei. 17 (4): 537–558. Bibcode:2003EPJA...17..537K. doi:10.1140/epja/i2002-10162-1. ISSN 1434-601X. S2CID 122384851. Retrieved 23 June 2023.
  4. [4]
    Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (1 March 2021). "The NUBASE2020 evaluation of nuclear physics properties *". Chinese Physics C, High Energy Physics and Nuclear Physics. 45 (3): 030001. Bibcode:2021ChPhC..45c0001K. doi:10.1088/1674-1137/abddae. ISSN 1674-1137. OSTI 1774641. S2CID 233794940.
  5. [5]
    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
  6. [6]
    Cubiss, J. G.; Andreyev, A. N.; Barzakh, A. E.; Andel, B.; Antalic, S.; Cocolios, T. E.; Goodacre, T. Day; Fedorov, D. V.; Fedosseev, V. N.; Ferrer, R.; Fink, D. A.; Gaffney, L. P.; Ghys, L.; Huyse, M.; Kalaninová, Z.; Köster, U.; Marsh, B. A.; Molkanov, P. L.; Rossel, R. E.; Rothe, S.; Seliverstov, M. D.; Sels, S.; Sjödin, A. M.; Stryjczyk, M.; L.Truesdale, V.; Van Beveren, C.; Van Duppen, P.; Wilson, G. L. (2019-06-14). "Fine structure in the α decay of At218". Physical Review C. 99 (6). American Physical Society (APS): 064317. doi:10.1103/physrevc.99.064317. ISSN 2469-9985. S2CID 197508141.
  7. [7]
    Lavrukhina & Pozdnyakov 1966, p. 232.
  8. [8]
    Rankama, Kalervo (1956). Isotope geology (2nd ed.). Pergamon Press. p. 403. ISBN 978-0-470-70800-2.
  9. [9]
    Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
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