Isotopes of astatine

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.

Isotopes of astatine (85At)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
209At synth 5.41 h β+ 209Po
α 205Bi
210At synth 8.1 h β+ 210Po
α 206Bi
211At synth 7.21 h ε 211Po
α 207Bi

List of isotopes
Nuclide
[n 1]		 Z N Isotopic mass (Da)
[n 2][n 3]		 Half-life
 Decay
mode
[n 4]		 Daughter
isotope
[n 5]		 Spin and
parity
[n 6][n 7]		 Isotopic
abundance
Excitation energy[n 7]
188At[2] 85 103 190+350
−80 μs		 α (~50%) 184Bi
p (~50%) 187Po
190At[2] 85 105 1.0+14
−4 ms		 α 186Bi (10−)
191At[3] 85 106 1.7+11
−5 ms		 α 187Bi (1/2+)
191mAt 50(30) keV 2.1+4
−3 ms		 α 187Bi (7/2−)
192At[4] 85 107 192.00314(28) 11.5(6) ms α 188Bi 3+#
β+ (rare) 192Po
β+, SF (0.42%) (various)
192mAt 0(40) keV 88(6) ms α 188mBi (9−, 10−)
β+ (rare) 192Po
β+, SF (0.42%) (various)
193At[4] 85 108 192.99984(6) 28+5
−4 ms		 α 189Bi (1/2+)
193m1At 8(9) keV 21(5) ms α 189m1Bi (7/2−)
193m2At 42(9) keV 27+4
−3 ms		 IT (76%) 193At (13/2+)
α (24%) 189m2Bi
194At[4] 85 109 193.99873(20) 286(7) ms α (91.7%#) 190Bi (5-)
β+ (8.3%#) 194Po
β+, SF (0.032%#) (various)
194mAt -20(40) keV 323(7) ms α (91.7%#) 190Bi (10-)
β+ (8.3%#) 194Po
β+, SF (0.032%#) (various)
195At[4] 85 110 194.996268(10) 290(20) ms α 191mBi (1/2+)
β+? 195Po
195mAt 29(7) keV 143(3) ms α (88%) 191Bi (7/2-)
IT (12%) 195At
β+? 195Po
196At[4] 85 111 195.99579(6) 377(4) ms α (97.5%) 192Bi (3+)
β+ (2.5%) 196Po
196m1At −40(40) keV 20# ms α 192mBi (10−)
196m2At 157.9(1) keV 11(2) μs IT 196At (5+)
197At[4] 85 112 196.99319(5) 388.2(5.6) ms α (96.1%) 193Bi (9/2−)
β+ (3.9%) 197Po
197m1At 45(8) keV 2.0(2) s α 193m1Bi (1/2+)
IT (<0.004%) 197At
β+? 197Po
197m2At 310.7(2) keV 1.3(2) μs IT 197At (13/2+)
198At 85 113 197.99284(5) 4.2(3) s α (94%) 194Bi (3+)
β+ (6%) 198Po
198mAt 330(90)# keV 1.0(2) s (10−)
199At 85 114 198.99053(5) 6.92(13) s α (89%) 195Bi (9/2−)
β+ (11%) 199Po
200At 85 115 199.990351(26) 43.2(9) s α (57%) 196Bi (3+)
β+ (43%) 200Po
200m1At 112.7(30) keV 47(1) s α (43%) 196Bi (7+)
IT 200At
β+ 200Po
200m2At 344(3) keV 3.5(2) s (10−)
201At 85 116 200.988417(9) 85(3) s α (71%) 197Bi (9/2−)
β+ (29%) 201Po
202At 85 117 201.98863(3) 184(1) s β+ (88%) 202Po (2, 3)+
α (12%) 198Bi
202m1At 190(40) keV 182(2) s (7+)
202m2At 580(40) keV 460(50) ms (10−)
203At 85 118 202.986942(13) 7.37(13) min β+ (69%) 203Po 9/2−
α (31%) 199Bi
204At 85 119 203.987251(26) 9.2(2) min β+ (96%) 204Po 7+
α (3.8%) 200Bi
204mAt 587.30(20) keV 108(10) ms IT 204At (10−)
205At 85 120 204.986074(16) 26.2(5) min β+ (90%) 205Po 9/2−
α (10%) 201Bi
205mAt 2339.65(23) keV 7.76(14) μs 29/2+
206At 85 121 205.986667(22) 30.6(13) min β+ (99.11%) 206Po (5)+
α (0.9%) 202Bi
206mAt 807(3) keV 410(80) ns (10)−
207At 85 122 206.985784(23) 1.80(4) h β+ (91%) 207Po 9/2−
α (8.6%) 203Bi
208At 85 123 207.986590(28) 1.63(3) h β+ (99.5%) 208Po 6+
α (0.55%) 204Bi
209At 85 124 208.986173(8) 5.41(5) h β+ (96%) 209Po 9/2−
α (4.0%) 205Bi
210At 85 125 209.987148(8) 8.1(4) h β+ (99.8%) 210Po (5)+
α (0.18%) 206Bi
210m1At 2549.6(2) keV 482(6) μs (15)−
210m2At 4027.7(2) keV 5.66(7) μs (19)+
211At 85 126 210.9874963(30) 7.214(7) h EC (58.2%) 211Po 9/2−
α (42%) 207Bi
212At 85 127 211.990745(8) 0.314(2) s α (99.95%) 208Bi (1−)
β+ (0.05%) 212Po
β− (2×10−6%) 212Rn
212m1At 223(7) keV 0.119(3) s α (99%) 208Bi (9−)
IT (1%) 212At
212m2At 4771.6(11) keV 152(5) μs (25−)
213At 85 128 212.992937(5) 125(6) ns α 209Bi 9/2−
214At 85 129 213.996372(5) 558(10) ns α 210Bi 1−
214m1At 59(9) keV 265(30) ns
214m2At 231(6) keV 760(15) ns 9−
215At 85 130 214.998653(7) 0.10(2) ms α 211Bi 9/2− Trace[n 8]
216At 85 131 216.002423(4) 0.30(3) ms α (99.99%) 212Bi 1−
β− (.006%) 216Rn
EC (3×10−7%) 216Po
216mAt 413(5) keV 100# μs (9−)
217At 85 132 217.004719(5) 32.3(4) ms α (99.98%) 213Bi 9/2− Trace[n 9]
β− (.012%) 217Rn
218At 85 133 218.008694(12) 1.27(6) s[5] α (99.9%) 214Bi 1−# Trace[n 10]
β− (0.10%) 218Rn
219At 85 134 219.011162(4) 56(3) s α (97%) 215Bi (9/2−) Trace[n 8]
β− (3.0%) 219Rn
220At 85 135 220.015433(15) 3.71(4) min β− (92%) 220Rn 3(−#)
α (8.0%) 216Bi
221At 85 136 221.018017(15) 2.3(2) min β− 221Rn 3/2−#
222At 85 137 222.022494(17) 54(10) s β− 222Rn
223At 85 138 223.025151(15) 50(7) s β− 223Rn 3/2−#
224At 85 139 224.029749(24) 2.5(1.5) min β− 224Rn 2+#
225At 85 140 225.03253(32)# 3# s β− 225Rn 1/2+#
226At 85 141 226.03721(32)# 7# min β− 226Rn 2+#
227At 85 142 227.04018(32)# 5# s β− 227Rn 1/2+#
228At 85 143 228.04496(43)# 1# min β− 228Rn 3+#
229At 85 144 229.04819(43)# 1# s β− 229Rn 1/2+#
This table header & footer:
  1. mAt – Excited nuclear isomer.
  2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  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. Modes of decay:
    EC:Electron capture
    IT:Isomeric transition
  5. Bold italics symbol as daughter – Daughter product is nearly stable.
  6. ( ) spin value – Indicates spin with weak assignment arguments.
  7. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  8. Intermediate decay product of 235U
  9. Intermediate decay product of 237Np
  10. Intermediate decay product of 238U

Alpha decay
Alpha decay characteristics for sample astatine isotopes[lower-alpha 1]
Mass
number		 Mass
excess[6]		 Mass
excess of
daughter[6]		 Average
energy of
alpha
decay		 Half-life[6] Probability
of alpha
decay[6]		 Alpha
decay
half-life
207 −13.243 MeV −19.116 MeV 5.873 MeV 1.80 h 8.6% 20.9 h
208 −12.491 MeV −18.243 MeV 5.752 MeV 1.63 h 0.55% 12.3 d
209 −12.880 MeV −18.638 MeV 5.758 MeV 5.41 h 4.1% 5.5 d
210 −11.972 MeV −17.604 MeV 5.632 MeV 8.1 h 0.175% 193 d
211 −11.647 MeV −17.630 MeV 5.983 MeV 7.21 h 41.8% 17.2 h
212 −8.621 MeV −16.436 MeV 7.825 MeV 0.31 s ≈100% 0.31 s
213 −6.579 MeV −15.834 MeV 9.255 MeV 125 ns 100% 125 ns
214 −3.380 MeV −12.366 MeV 8.986 MeV 558 ns 100% 558 ns
219 10.397 MeV 4.073 MeV 6.324 MeV 56 s 97% 58 s
220 14.350 MeV 8.298 MeV 6.052 MeV 3.71 min 8% 46.4 min
221[lower-alpha 2] 16.810 MeV 11.244 MeV 5.566 MeV 2.3 min experimentally
alpha stable		 ∞

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.[6]

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.[6][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 astatine-213, astatine-214, and astatine-216m.[6] Among other isotopes: astatine-210 and the lighter isotopes decay by positron emission; astatine-216 and the heavier isotopes undergo beta decay; astatine-212 can decay either way; and astatine-211 decays by electron capture instead.[6]

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.[6]

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. 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. Kokkonen, Henna. "Decay properties of the new isotopes 188At and 190At" (PDF). University of Jyväskylä. Retrieved 8 June 2023.
  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. 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. Retrieved 4 July 2023.
  5. 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. American Physical Society (APS). 99 (6): 064317. doi:10.1103/physrevc.99.064317. ISSN 2469-9985. S2CID 197508141.
  6. 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
  7. Lavrukhina & Pozdnyakov 1966, p. 232.
  8. Rankama, Kalervo (1956). Isotope geology (2nd ed.). Pergamon Press. p. 403. ISBN 978-0-470-70800-2.
  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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