# Isotopes of astatine

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

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Isotopic abundance |
| Isotopic abundance |||
| $^{188}$At | 85 | 103 | | 190+350 −80 μs | α (~50%) | $^{184}$Bi | | |
| $^{188}$At | 85 | 103 | | 190+350 −80 μs | p (~50%) | $^{187}$Po | | |
| $^{190}$At | 85 | 105 | | 1.0+14 −4 ms | α | $^{186}$Bi | (10−) | |
| $^{191}$At | 85 | 106 | | 1.7+11 −5 ms | α | $^{187}$Bi | (1/2+) | |
| $^{191m}$At | 50(30) keV | 50(30) keV | 50(30) keV | 2.1+4 −3 ms | α | $^{187}$Bi | (7/2−) | |
| $^{192}$At | 85 | 107 | 192.00314(28) | 11.5(6) ms | α | $^{188}$Bi | 3+# | |
| $^{192}$At | 85 | 107 | 192.00314(28) | 11.5(6) ms | β$^+$ (rare) | $^{192}$Po | 3+# | |
| $^{192}$At | 85 | 107 | 192.00314(28) | 11.5(6) ms | β$^+$, SF (0.42%) | (various) | 3+# | |
| $^{192m}$At | 0(40) keV | 0(40) keV | 0(40) keV | 88(6) ms | α | $^{188m}$Bi | (9−, 10−) | |
| $^{192m}$At | 0(40) keV | 0(40) keV | 0(40) keV | 88(6) ms | β$^+$ (rare) | $^{192}$Po | (9−, 10−) | |
| $^{192m}$At | 0(40) keV | 0(40) keV | 0(40) keV | 88(6) ms | β$^+$, SF (0.42%) | (various) | (9−, 10−) | |
| $^{193}$At | 85 | 108 | 192.99984(6) | 28+5 −4 ms | α | $^{189}$Bi | (1/2+) | |
| $^{193m1}$At | 8(9) keV | 8(9) keV | 8(9) keV | 21(5) ms | α | $^{189m1}$Bi | (7/2−) | |
| $^{193m2}$At | 42(9) keV | 42(9) keV | 42(9) keV | 27+4 −3 ms | IT (76%) | $^{193}$At | (13/2+) | |
| $^{193m2}$At | 42(9) keV | 42(9) keV | 42(9) keV | 27+4 −3 ms | α (24%) | $^{189m2}$Bi | (13/2+) | |
| $^{194}$At | 85 | 109 | 193.99873(20) | 286(7) ms | α (91.7%#) | $^{190}$Bi | (5-) | |
| $^{194}$At | 85 | 109 | 193.99873(20) | 286(7) ms | β$^+$ (8.3%#) | $^{194}$Po | (5-) | |
| $^{194}$At | 85 | 109 | 193.99873(20) | 286(7) ms | β$^+$, SF (0.032%#) | (various) | (5-) | |
| $^{194m}$At | -20(40) keV | -20(40) keV | -20(40) keV | 323(7) ms | α (91.7%#) | $^{190}$Bi | (10-) | |
| $^{194m}$At | -20(40) keV | -20(40) keV | -20(40) keV | 323(7) ms | β$^+$ (8.3%#) | $^{194}$Po | (10-) | |
| $^{194m}$At | -20(40) keV | -20(40) keV | -20(40) keV | 323(7) ms | β$^+$, SF (0.032%#) | (various) | (10-) | |
| $^{195}$At | 85 | 110 | 194.996268(10) | 290(20) ms | α | $^{191m}$Bi | (1/2+) | |
| $^{195}$At | 85 | 110 | 194.996268(10) | 290(20) ms | β$^+$? | $^{195}$Po | (1/2+) | |
| $^{195m}$At | 29(7) keV | 29(7) keV | 29(7) keV | 143(3) ms | α (88%) | $^{191}$Bi | (7/2-) | |
| $^{195m}$At | 29(7) keV | 29(7) keV | 29(7) keV | 143(3) ms | IT (12%) | $^{195}$At | (7/2-) | |
| $^{195m}$At | 29(7) keV | 29(7) keV | 29(7) keV | 143(3) ms | β$^+$? | $^{195}$Po | (7/2-) | |
| $^{196}$At | 85 | 111 | 195.99579(6) | 377(4) ms | α (97.5%) | $^{192}$Bi | (3+) | |
| $^{196}$At | 85 | 111 | 195.99579(6) | 377(4) ms | β$^+$ (2.5%) | $^{196}$Po | (3+) | |
| $^{196m1}$At | −40(40) keV | −40(40) keV | −40(40) keV | 20# ms | α | $^{192m}$Bi | (10−) | |
| $^{196m2}$At | 157.9(1) keV | 157.9(1) keV | 157.9(1) keV | 11(2) μs | IT | $^{196}$At | (5+) | |
| $^{197}$At | 85 | 112 | 196.99319(5) | 388.2(5.6) ms | α (96.1%) | $^{193}$Bi | (9/2−) | |
| $^{197}$At | 85 | 112 | 196.99319(5) | 388.2(5.6) ms | β$^+$ (3.9%) | $^{197}$Po | (9/2−) | |
| $^{197m1}$At | 45(8) keV | 45(8) keV | 45(8) keV | 2.0(2) s | α | $^{193m1}$Bi | (1/2+) | |
| $^{197m1}$At | 45(8) keV | 45(8) keV | 45(8) keV | 2.0(2) s | IT (<0.004%) | $^{197}$At | (1/2+) | |
| $^{197m1}$At | 45(8) keV | 45(8) keV | 45(8) keV | 2.0(2) s | β$^+$? | $^{197}$Po | (1/2+) | |
| $^{197m2}$At | 310.7(2) keV | 310.7(2) keV | 310.7(2) keV | 1.3(2) μs | IT | $^{197}$At | (13/2+) | |
| $^{198}$At | 85 | 113 | 197.99284(5) | 4.2(3) s | α (94%) | $^{194}$Bi | (3+) | |
| $^{198}$At | 85 | 113 | 197.99284(5) | 4.2(3) s | β$^+$ (6%) | $^{198}$Po | (3+) | |
| $^{198m}$At | 330(90)# keV | 330(90)# keV | 330(90)# keV | 1.0(2) s | | | (10−) | |
| $^{199}$At | 85 | 114 | 198.99053(5) | 6.92(13) s | α (89%) | $^{195}$Bi | (9/2−) | |
| $^{199}$At | 85 | 114 | 198.99053(5) | 6.92(13) s | β$^+$ (11%) | $^{199}$Po | (9/2−) | |
| $^{200}$At | 85 | 115 | 199.990351(26) | 43.2(9) s | α (57%) | $^{196}$Bi | (3+) | |
| $^{200}$At | 85 | 115 | 199.990351(26) | 43.2(9) s | β$^+$ (43%) | $^{200}$Po | (3+) | |
| $^{200m1}$At | 112.7(30) keV | 112.7(30) keV | 112.7(30) keV | 47(1) s | α (43%) | $^{196}$Bi | (7+) | |
| $^{200m1}$At | 112.7(30) keV | 112.7(30) keV | 112.7(30) keV | 47(1) s | IT | $^{200}$At | (7+) | |
| $^{200m1}$At | 112.7(30) keV | 112.7(30) keV | 112.7(30) keV | 47(1) s | β$^+$ | $^{200}$Po | (7+) | |
| $^{200m2}$At | 344(3) keV | 344(3) keV | 344(3) keV | 3.5(2) s | | | (10−) | |
| $^{201}$At | 85 | 116 | 200.988417(9) | 85(3) s | α (71%) | $^{197}$Bi | (9/2−) | |
| $^{201}$At | 85 | 116 | 200.988417(9) | 85(3) s | β$^+$ (29%) | $^{201}$Po | (9/2−) | |
| $^{202}$At | 85 | 117 | 201.98863(3) | 184(1) s | β$^+$ (88%) | $^{202}$Po | (2, 3)+ | |
| $^{202}$At | 85 | 117 | 201.98863(3) | 184(1) s | α (12%) | $^{198}$Bi | (2, 3)+ | |
| $^{202m1}$At | 190(40) keV | 190(40) keV | 190(40) keV | 182(2) s | | | (7+) | |
| $^{202m2}$At | 580(40) keV | 580(40) keV | 580(40) keV | 460(50) ms | | | (10−) | |
| $^{203}$At | 85 | 118 | 202.986942(13) | 7.37(13) min | β$^+$ (69%) | $^{203}$Po | 9/2− | |
| $^{203}$At | 85 | 118 | 202.986942(13) | 7.37(13) min | α (31%) | $^{199}$Bi | 9/2− | |
| $^{204}$At | 85 | 119 | 203.987251(26) | 9.2(2) min | β$^+$ (96%) | $^{204}$Po | 7+ | |
| $^{204}$At | 85 | 119 | 203.987251(26) | 9.2(2) min | α (3.8%) | $^{200}$Bi | 7+ | |
| $^{204m}$At | 587.30(20) keV | 587.30(20) keV | 587.30(20) keV | 108(10) ms | IT | $^{204}$At | (10−) | |
| $^{205}$At | 85 | 120 | 204.986074(16) | 26.2(5) min | β$^+$ (90%) | $^{205}$Po | 9/2− | |
| $^{205}$At | 85 | 120 | 204.986074(16) | 26.2(5) min | α (10%) | $^{201}$Bi | 9/2− | |
| $^{205m}$At | 2339.65(23) keV | 2339.65(23) keV | 2339.65(23) keV | 7.76(14) μs | | | 29/2+ | |
| $^{206}$At | 85 | 121 | 205.986667(22) | 30.6(13) min | β$^+$ (99.11%) | $^{206}$Po | (5)+ | |
| $^{206}$At | 85 | 121 | 205.986667(22) | 30.6(13) min | α (0.9%) | $^{202}$Bi | (5)+ | |
| $^{206m}$At | 807(3) keV | 807(3) keV | 807(3) keV | 410(80) ns | | | (10)− | |
| $^{207}$At | 85 | 122 | 206.985784(23) | 1.80(4) h | β$^+$ (91%) | $^{207}$Po | 9/2− | |
| $^{207}$At | 85 | 122 | 206.985784(23) | 1.80(4) h | α (8.6%) | $^{203}$Bi | 9/2− | |
| $^{208}$At | 85 | 123 | 207.986590(28) | 1.63(3) h | β$^+$ (99.5%) | $^{208}$Po | 6+ | |
| $^{208}$At | 85 | 123 | 207.986590(28) | 1.63(3) h | α (0.55%) | $^{204}$Bi | 6+ | |
| $^{209}$At | 85 | 124 | 208.986173(8) | 5.41(5) h | β$^+$ (96%) | $^{209}$Po | 9/2− | |
| $^{209}$At | 85 | 124 | 208.986173(8) | 5.41(5) h | α (4.0%) | $^{205}$Bi | 9/2− | |
| $^{210}$At | 85 | 125 | 209.987148(8) | 8.1(4) h | β$^+$ (99.8%) | $^{210}$Po | (5)+ | |
| $^{210}$At | 85 | 125 | 209.987148(8) | 8.1(4) h | α (0.18%) | $^{206}$Bi | (5)+ | |
| $^{210m1}$At | 2549.6(2) keV | 2549.6(2) keV | 2549.6(2) keV | 482(6) μs | | | (15)− | |
| $^{210m2}$At | 4027.7(2) keV | 4027.7(2) keV | 4027.7(2) keV | 5.66(7) μs | | | (19)+ | |
| $^{211}$At | 85 | 126 | 210.9874963(30) | 7.214(7) h | EC (58.2%) | $^{211}$Po | 9/2− | |
| $^{211}$At | 85 | 126 | 210.9874963(30) | 7.214(7) h | α (42%) | $^{207}$Bi | 9/2− | |
| $^{212}$At | 85 | 127 | 211.990745(8) | 314(2) ms | α | $^{208}$Bi | (1−) | |
| $^{212m1}$At | 223(7) keV | 223(7) keV | 223(7) keV | 119(3) ms | α | $^{208}$Bi | (9−) | |
| $^{212m2}$At | 4771.6(11) keV | 4771.6(11) keV | 4771.6(11) keV | 152(5) μs | IT | $^{212}$At | (25−) | |
| $^{213}$At | 85 | 128 | 212.992937(5) | 125(6) ns | α | $^{209}$Bi | 9/2− | |
| $^{214}$At | 85 | 129 | 213.996372(5) | 558(10) ns | α | $^{210}$Bi | 1− | |
| $^{214m1}$At | 59(9) keV | 59(9) keV | 59(9) keV | 265(30) ns | α | $^{210}$Bi | | |
| $^{214m2}$At | 232(5) keV | 232(5) keV | 232(5) keV | 760(15) ns | α | $^{210}$Bi | 9− | |
| $^{215}$At | 85 | 130 | 214.998653(7) | 0.10(2) ms | α | $^{211}$Bi | 9/2− | Trace |
| $^{216}$At | 85 | 131 | 216.002423(4) | 0.30(3) ms | α | $^{212}$Bi | 1− | |
| $^{216m}$At | 161(11) keV | 161(11) keV | 161(11) keV | 100# μs | α | $^{212}$Bi | 9−# | |
| $^{217}$At | 85 | 132 | 217.004719(5) | 32.3(4) ms | α (99.98%) | $^{213}$Bi | 9/2− | Trace |
| $^{217}$At | 85 | 132 | 217.004719(5) | 32.3(4) ms | β$^−$ (.012%) | $^{217}$Rn | 9/2− | Trace |
| $^{218}$At | 85 | 133 | 218.008694(12) | 1.27(6) s | α (99.9%) | $^{214}$Bi | (2−,3−) | Trace |
| $^{218}$At | 85 | 133 | 218.008694(12) | 1.27(6) s | β$^−$ (0.1%) | $^{218}$Rn | (2−,3−) | Trace |
| $^{219}$At | 85 | 134 | 219.011162(4) | 56(3) s | α (97%) | $^{215}$Bi | (9/2−) | Trace |
| $^{219}$At | 85 | 134 | 219.011162(4) | 56(3) s | β$^−$ (3.0%) | $^{219}$Rn | (9/2−) | Trace |
| $^{220}$At | 85 | 135 | 220.015433(15) | 3.71(4) min | β$^−$ (92%) | $^{220}$Rn | 3(−#) | |
| $^{220}$At | 85 | 135 | 220.015433(15) | 3.71(4) min | α (8.0%) | $^{216}$Bi | 3(−#) | |
| $^{221}$At | 85 | 136 | 221.018017(15) | 2.3(2) min | β$^−$ | $^{221}$Rn | 3/2−# | |
| $^{222}$At | 85 | 137 | 222.022494(17) | 54(10) s | β$^−$ | $^{222}$Rn | | |
| $^{223}$At | 85 | 138 | 223.025151(15) | 50(7) s | β$^−$ | $^{223}$Rn | 3/2−# | |
| $^{224}$At | 85 | 139 | 224.029749(24) | 2.5(1.5) min | β$^−$ | $^{224}$Rn | 2+# | |
| $^{225}$At | 85 | 140 | 225.03253(32)# | 3# s | β$^−$ | $^{225}$Rn | 1/2+# | |
| $^{226}$At | 85 | 141 | 226.03721(32)# | 7# min | β$^−$ | $^{226}$Rn | 2+# | |
| $^{227}$At | 85 | 142 | 227.04018(32)# | 5# s | β$^−$ | $^{227}$Rn | 1/2+# | |
| $^{228}$At | 85 | 143 | 228.04496(43)# | 1# min | β$^−$ | $^{228}$Rn | 3+# | |
| $^{229}$At | 85 | 144 | 229.04819(43)# | 1# s | β$^−$ | $^{229}$Rn | 1/2+# | |
| This table header & footer: view |||||||||
* ↑ $^m$At – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* ↑ Modes of decay: EC:Electron capture IT:Isomeric transition
* ↑ Bold italics symbol as daughter – Daughter product is nearly stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* 1 2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Theoretically capable of β$^+$ decay to $^{212}$Po or β$^−$ decay to $^{212}$Rn'"`UNIQ--ref-00000023-QINU`"''"`UNIQ--ref-00000025-QINU`"''"`UNIQ--ref-00000026-QINU`"'
* ↑ Theoretically capable of electron capture to $^{213}$Po'"`UNIQ--ref-00000028-QINU`"'
* ↑ Theoretically capable of isomeric transition to $^{214}$At'"`UNIQ--ref-0000002B-QINU`"'
* ↑ Theoretically capable of isomeric transition to $^{214}$At'"`UNIQ--ref-0000002E-QINU`"''"`UNIQ--ref-0000002F-QINU`"'
* 1 2 Intermediate decay product of $^{235}$U
* ↑ Theoretically capable of electron capture to $^{216}$Po or β$^−$ decay to $^{216}$Rn'"`UNIQ--ref-00000031-QINU`"''"`UNIQ--ref-00000033-QINU`"''"`UNIQ--ref-00000034-QINU`"'
* ↑ Intermediate decay product of $^{237}$Np
* ↑ Intermediate decay product of $^{238}$U

## Alpha decay

Alpha decay characteristics for sample astatine isotopes :
| Mass number | Mass excess | Mass excess of daughter | Average energy of alpha decay | Half-life | Probability of alpha decay | 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 | 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, 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.
Alpha decay energy follows the same trend as for other heavy elements. 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. 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. Even though heavier astatine isotopes release less energy, no long-lived astatine isotope exists; this happens due to the increasing role of beta decay. 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), though nuclear mass measurements reveal that $^{215}$At is in fact beta-stable, as it has the lowest mass of all isobars with A = 215. A beta decay mode has been found for all other astatine isotopes except for $^{212-216}$At and their isomers. 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. 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.