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Isotopes of astatine

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Astatine (85At) has 41 known isotopes, all of which are radioactive, whose mass numbers range from 188 to 229 except 189; they are accompanied by almost as many metastable excited states. The longest-lived isotope is 210At, which has a half-life of 8.1 hours, followed by the medically useful 211At, with a half-life of 7.214 hours. The longest-lived isomer is 202m1At with a half-life of just over 3 minutes. However, the longest-lived isotope existing in naturally occurring decay chains is 219At with a half-life of only 56 seconds.

Quick facts Main isotopes, Decay ...
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List of isotopes


More information Nuclide, Z ...
  1. [1]
    mAt – Excited nuclear isomer.
  2. [2]
    ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. [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. [4]
    Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
  5. [5]
    Bold italics symbol as daughter – Daughter product is nearly stable.
  6. [6]
    ( ) spin value – Indicates spin with weak assignment arguments.
  7. [7]
    # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  8. [8]
    Order of ground state and isomer is uncertain.
  9. [9]
    Theoretically capable of β+ decay to 212Po or β− decay to 212Rn; the branching ratios are expected to be <3×10−2% and <2×10−6% (partial half-lives >17.4 min and >182 d) respectively.[5]
  10. [10]
    Theoretically capable of electron capture to 213Po; the branching ratio is expected to be <2.5×10−12% (partial half-life >57.9 d).[6]
  11. [11]
    Intermediate decay product of 235U
  12. [12]
    Theoretically capable of electron capture to 216Po or β− decay to 216Rn; the branching ratios are expected to be <3×10−7% and <6×10−3% (partial half-lives >1.2 d and >5.0 s) respectively.[8]
  13. [13]
    Intermediate decay product of 237Np
  14. [14]
    Intermediate decay product of 238U
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Alpha decay

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More information Mass number, Mass excess ...

Alpha decay energy follows the same trend as for other heavy elements.[10] The lighter astatine isotopes have quite high decay energies, which become lower as more neutrons are added, reaching a minimum at 125 neutrons (astatine-210), even though 126 (astatine-211) is the magic number. The decay energies increase much more steeply, though, on the next two steps, reaching a high at 128 neutrons where the alpha-decay product would have the magic number of 126. Here this is astatine-213, releasing the highest energy and having the shortest life (125 ns) of all the isotopes. The energy then declines again, and alpha lifetimes increase quickly, no long-lived astatine isotope exists; this happens due to the increasing role of beta decay.[10] 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),[11] though nuclear mass measurements reveal that 215At is in fact beta-stable, as it has the lowest mass of all isobars with A = 215.[1] A beta decay mode has been found for all other astatine isotopes except for 212-216At and their isomers.[1] Among other isotopes, if they do not undergo alpha decay: astatine-210 and the lighter isotopes decay by electron capture or positron emission, 211 by electron capture only, and astatine-217 and heavier isotopes undergo β- decay. Astatine-212, 214, and 216 should be able to decay either way.

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See also

Daughter products other than astatine

Notes

  1. [a]
    In the table, under the words "mass excess", the energy equivalents are given rather than the real mass excesses; "mass excess of 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.

References

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