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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.

List of isotopes

|-id=Astatine-188 | α (~50%)

184Bi
p (~50%)
187Po
-id=Astatine-190
190At

| | | α | 186Bi | (10−) | |-id=Astatine-191 | 191At | 191.004148(17) | 2.1(8) ms | α | 187Bi | 1/2+ | |-id=Astatine-191m | 2.2(4) ms | α | 187Bi | (7/2−) | |-id=Astatine-192 | 192At | 192.003141(3) | 11.5(6) ms | α | 188Bi | 3+# | |-id=Astatine-192m | 88(6) ms | α | 188mBi | (9−, 10−) | |-id=Astatine-193 | 193At | 192.999928(23) | 29(5) ms | α | 189Bi | 1/2+ | |-id=Astatine-193m1 | 21(5) ms | α | 189m1Bi | 7/2− | |-id=Astatine-193m2 | IT (76%)

193At
α (24%)
189m2Bi
-id=Astatine-194
α (91.7%#)
190Bi
-
β+ (8.3%#)
194Po
-
β+, SF (0.032%#)
(various)
-id=Astatine-194m
α (91.7%#)
190Bi
-
β+ (8.3%#)
194Po
-
β+, SF (0.032%#)
(various)
-id=Astatine-195
α
191mBi
-
β+ ?
195Po
-id=Astatine-195m
α (88%)
191Bi
-
IT (12%)
195At
-
β+?
195Po
-id=Astatine-196
α (97.5%)
192Bi
-
β+ (2.5%)
196Po
-
β+, SF (0.009%)
(various)
-id=Astatine-196m1
20# ms
α
192mBi
10−#

| |-id=Astatine-196m2 | 11(2) μs | IT | 196At | (5+) | |-id=Astatine-197 | α (96.1%)

193Bi
β+ (3.9%)
197Po
-id=Astatine-197m1
α
193m1Bi
-
IT (
197At
-
β+?
197Po
-id=Astatine-197m2
1.3(2) μs
IT
197At
13/2+

| |-id=Astatine-198 | α (97%)

194Bi
β+ (3%)
198Po
-id=Astatine-198m
α (93%)

| |- | β+ ?

198Po
IT ?
198Po
-id=Astatine-199
α (89%)
195Bi
-
β+ (11%)
199Po
-id=Astatine-199m1
IT (99%)

| |- | α (1%) | 195Bi |-id=Astatine-199m2 | 70(20) ns | IT | | 13/2+ | |-id=Astatine-199m3 | 800(50) ns | IT | | (29/2+) | |-id=Astatine-200 | α (52%)

196Bi
β+ (48%)
200Po
-id=Astatine-200m1
β+ (57%)
200Po
-
α (43%)
196Bi
-
IT ?
200At
-id=Astatine-200m2
IT ?
200At
-
α (10.5%)
196Bi
-
β+ ?
200Po
-id=Astatine-201
α (71%)
197Bi
-
β+ (29%)
201Po
-id=Astatine-201m1
45(3) ms
IT

| | 1/2+ | |-id=Astatine-201m2 | 3.39(9) μs | IT | | 29/2+ | |-id=Astatine-202 | β+ (88%)

202Po
α (12%)
198Bi
-id=Astatine-202m1
β+ (91.5%)
202Po
-
α (8.5%)
198Bi
-
IT ?
202At
-id=Astatine-202m2
IT (99.904%)
202At
-
α (0.096%)
198Bi
-
IT ?
202At
-id=Astatine-203
β+ (69%)
203Po
-
α (31%)
199Bi
-id=Astatine-203m1
3.5(6) ms
IT

| | 1/2+ | |-id=Astatine-203m2 | 9.77(21) μs | IT | | 29/2+ | |-id=Astatine-204 | β+ (96.2%)

204Po
α (3.8%)
200Bi
-id=Astatine-204m
108(10) ms
IT
204At
10−

| |-id=Astatine-205 | β+ (90%)

205Po
α (10%)
201Bi
-id=Astatine-205m
7.76(14) μs
IT
205At
29/2+

| |-id=Astatine-206 | β+ (99.1%)

206Po
α (0.9%)
202Bi
-id=Astatine-206m
813(21) ns
IT
206At
(10)−

| |-id=Astatine-207 | β+ (~90%)

207Po
α (~10%)
203Bi
-id=Astatine-207m
108(2) ns
IT
207At
25/2+

| |-id=Astatine-208 | β+ (99.45%)

208Po
α (0.55%)
204Bi
-id=Astatine-208m
1.5(2) μs
IT
208At
16-

| |-id=Astatine-209 | β+ (96.1%)

209Po
α (3.9%)
205Bi
-id=Astatine-209m
916(10) ns
IT
209At
29/2+

| |-id=Astatine-210 | β+ (99.825%)

210Po
α (0.175%)
206Bi
-id=Astatine-210m1
482(6) ns
IT
210At
(15)−

| |-id=Astatine-210m2 | 5.66(7) μs | IT | 210At | (19)+ | |-id=Astatine-211 | EC (58.2%)

211Po
α (41.8%)
207Bi
-id=Astatine-211m
4.23(7) μs
IT
211At
(39/2-)

| |-id=Astatine-212 | 212At | 211.9907373(26) | 314(3) ms | α | 208Bi | (1−) | |-id=Astatine-212m1 | 119(3) ms | α | 208Bi | (9−) | |-id=Astatine-212m2 | 152(5) μs | IT | 212At | (25−) | |-id=Astatine-213 | 213At | 212.992937(5) | 125(6) ns | α | 209Bi | 9/2− | |-id=Astatine-213m1 | 110(17) ns | IT | 213At | 25/2-# | |-id=Astatine-213m2 | 45(4) μs | IT | 213At | 49/2+# | |-id=Astatine-214 | 214At | 213.996372(4) | 558(10) ns | α | 210Bi | 1− | |-id=Astatine-214m1 | 265(30) ns | α | 210Bi | | |-id=Astatine-214m2 | 760(15) ns | α | 210mBi | 9− | |-id=Astatine-215 | 215At | 214.998651(7) | 37(3) μs | α | 211Bi | 9/2− | TraceIntermediate decay product of 235U |-id=Astatine-216 | 216At | 216.002423(4) | 300(30) μs | α | 212Bi | 1− | |-id=Astatine-216m | 100# μs | α | 212m1Bi | 9−# | |-id=Astatine-217 | α (99.992%)

213Bi
β− (0.008%)
217Rn
-id=Astatine-218
α (~100%)
214Bi
-
β− (?)
218Rn
-id=Astatine-219
α (93.6%)
215Bi
-
β− (6.4%)
219Rn
-id=Astatine-220
β− (92%)
220Rn
-
α (8%)
216Bi
-id=Astatine-221
221At
221.018017(15)
2.3(2) min
β−
221Rn
3/2−#

| |-id=Astatine-222 | 222At | 222.022494(17) | 54(10) s | β− | 222Rn | | |-id=Astatine-223 | 223At | 223.025151(15) | 50(7) s | β− | 223Rn | 3/2−# | |-id=Astatine-224 | 224At | 224.029749(24) | 2.5 +/- 1.5 min | β− | 224Rn | 2+# | |-id=Astatine-225 | 225At | 225.03253(32)# | 3# s (300 ns) | β− ? | 225Rn | 1/2+# | |-id=Astatine-226 | 226At | 226.03721(32)# | 7# min (300 ns) | β− ? | 226Rn | 2+# | |-id=Astatine-227 | 227At | 227.04018(32)# | 5# s (300 ns) | β− ? | 227Rn | 1/2+# | |-id=Astatine-228 | 228At | 228.04496(43)# | 1# min (300 ns) | β− ? | 228Rn | 3+# | |-id=Astatine-229 | 229At | 229.04819(43)# | 1# s (300 ns) | β− ? | 229Rn | 1/2+# |

Alpha decay

Mass number	Mass excess	Mass excess of daughter	Energy of alpha decay	Half-life	Probability of alpha decay	Alpha decay half-life	195	196	197	198	199	200	201	202	203	204	205	206	207	208	209	210	211	212	213	214	215	216	217	218	219	220	221
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				experimentally alpha stable	-

Alpha decay energy follows the same trend as for other heavy elements. 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. 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 215At 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 212-216At and their isomers. 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.

Notes

References

(29 May 2025). "New proton emitter 188At implies an interaction unprecedented in heavy nuclei". Nature Communications.
(20 June 2023). "Properties of the new α -decaying isotope At 190". Physical Review C.
"Adopted Levels for ²¹²At". NNDC Chart of Nuclides.
"Adopted Levels for ²¹³At". NNDC Chart of Nuclides.
"²¹⁴At α decay (760 ns)". NNDC Chart of Nuclides.
"Adopted Levels for ²¹⁶At". NNDC Chart of Nuclides.
"²¹⁶At α decay: J=9". NNDC Chart of Nuclides.
Rankama, Kalervo. (1956). "Isotope geology". Pergamon Press.

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