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Actinium (89Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic weight cannot be given. There are 34 known isotopes, from 203Ac to 236Ac, and 7 isomers. Three isotopes are found in nature, 225Ac, 227Ac and 228Ac, as intermediate decay products of, respectively, 237Np, 235U, and 232Th. 228Ac and 225Ac are extremely rare, so almost all natural actinium is 227Ac.
The most stable isotopes are 227Ac with a half-life of 21.772 years, 225Ac with a half-life of 10.0 days, and 226Ac with a half-life of 29.37 hours. All other isotopes have half-lives under 10 hours, and most under a minute. The shortest-lived known isotope is 217Ac with a half-life of 69 ns.
Purified 227Ac comes into equilibrium with its decay products (227Th and 223Fr) after 185 days. [2]
Nuclide [n 1] |
Historic name |
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] | |||||||||||||||||||
203Ac [3] | 89 | 114 | 56+269 −26 μs |
α | 199Fr | (1/2+) | |||||||||||||
204Ac [4] | 89 | 115 | 7.4+2.2 −1.4 ms |
α | 200Fr | ||||||||||||||
205Ac [5] | 89 | 116 | 7.7+2.7 −1.6 ms [4] |
α | 201Fr | 9/2−? | |||||||||||||
206Ac | 89 | 117 | 206.01450(8) | 25(7) ms | α | 202Fr | (3+) | ||||||||||||
206m1Ac | 80(50) keV | 15(6) ms | α | 202Fr | |||||||||||||||
206m2Ac | 290(110)# keV | 41(16) ms | α | 202mFr | (10−) | ||||||||||||||
207Ac | 89 | 118 | 207.01195(6) | 31(8) ms [27(+11−6) ms] |
α | 203Fr | 9/2−# | ||||||||||||
208Ac | 89 | 119 | 208.01155(6) | 97(16) ms [95(+24−16) ms] |
α (99%) | 204Fr | (3+) | ||||||||||||
β+ (1%) | 208Ra | ||||||||||||||||||
208mAc | 506(26) keV | 28(7) ms [25(+9−5) ms] |
α (89%) | 204Fr | (10−) | ||||||||||||||
IT (10%) | 208Ac | ||||||||||||||||||
β+ (1%) | 208Ra | ||||||||||||||||||
209Ac | 89 | 120 | 209.00949(5) | 92(11) ms | α (99%) | 205Fr | (9/2−) | ||||||||||||
β+ (1%) | 209Ra | ||||||||||||||||||
210Ac | 89 | 121 | 210.00944(6) | 350(40) ms | α (96%) | 206Fr | 7+# | ||||||||||||
β+ (4%) | 210Ra | ||||||||||||||||||
211Ac | 89 | 122 | 211.00773(8) | 213(25) ms | α (99.8%) | 207Fr | 9/2−# | ||||||||||||
β+ (.2%) | 211Ra | ||||||||||||||||||
212Ac | 89 | 123 | 212.00781(7) | 920(50) ms | α (97%) | 208Fr | 6+# | ||||||||||||
β+ (3%) | 212Ra | ||||||||||||||||||
213Ac | 89 | 124 | 213.00661(6) | 731(17) ms | α | 209Fr | (9/2−)# | ||||||||||||
β+ (rare) | 213Ra | ||||||||||||||||||
214Ac | 89 | 125 | 214.006902(24) | 8.2(2) s | α (89%) | 210Fr | (5+)# | ||||||||||||
β+ (11%) | 214Ra | ||||||||||||||||||
215Ac | 89 | 126 | 215.006454(23) | 0.17(1) s | α (99.91%) | 211Fr | 9/2− | ||||||||||||
β+ (.09%) | 215Ra | ||||||||||||||||||
216Ac | 89 | 127 | 216.008720(29) | 0.440(16) ms | α | 212Fr | (1−) | ||||||||||||
β+ (7×10−5%) | 216Ra | ||||||||||||||||||
216mAc | 44(7) keV | 443(7) µs | α | 212Fr | (9−) | ||||||||||||||
217Ac | 89 | 128 | 217.009347(14) | 69(4) ns | α | 213Fr | 9/2− | ||||||||||||
β+ (6.9×10−9%) | 217Ra | ||||||||||||||||||
217mAc | 2012(20) keV | 740(40) ns | (29/2)+ | ||||||||||||||||
218Ac | 89 | 129 | 218.01164(5) | 1.08(9) µs | α | 214Fr | (1−)# | ||||||||||||
218mAc | 584(50)# keV | 103(11) ns | (11+) | ||||||||||||||||
219Ac | 89 | 130 | 219.01242(5) | 11.8(15) µs | α | 215Fr | 9/2− | ||||||||||||
β+ (10−6%) | 219Ra | ||||||||||||||||||
220Ac | 89 | 131 | 220.014763(16) | 26.36(19) ms | α | 216Fr | (3−) | ||||||||||||
β+ (5×10−4%) | 220Ra | ||||||||||||||||||
221Ac | 89 | 132 | 221.01559(5) | 52(2) ms | α | 217Fr | 9/2−# | ||||||||||||
222Ac | 89 | 133 | 222.017844(6) | 5.0(5) s | α (99%) | 218Fr | 1− | ||||||||||||
β+ (1%) | 222Ra | ||||||||||||||||||
222mAc | 200(150)# keV | 1.05(7) min | α (88.6%) | 218Fr | high | ||||||||||||||
IT (10%) | 222Ac | ||||||||||||||||||
β+ (1.4%) | 222Ra | ||||||||||||||||||
223Ac | 89 | 134 | 223.019137(8) | 2.10(5) min | α (99%) | 219Fr | (5/2−) | ||||||||||||
EC (1%) | 223Ra | ||||||||||||||||||
CD (3.2×10−9%) | 209Bi 14C | ||||||||||||||||||
224Ac | 89 | 135 | 224.021723(4) | 2.78(17) h | β+ (90.9%) | 224Ra | 0− | ||||||||||||
α (9.1%) | 220Fr | ||||||||||||||||||
β− (1.6%) | 224Th | ||||||||||||||||||
225Ac [n 8] | 89 | 136 | 225.023230(5) | 10.0(1) d | α | 221Fr | (3/2−) | Trace [n 9] | |||||||||||
CD (6×10−10%) | 211Bi 14C | ||||||||||||||||||
226Ac | 89 | 137 | 226.026098(4) | 29.37(12) h | β− (83%) | 226Th | (1)(−#) | ||||||||||||
EC (17%) | 226Ra | ||||||||||||||||||
α (.006%) | 222Fr | ||||||||||||||||||
227Ac | Actinium [n 10] | 89 | 138 | 227.0277521(26) | 21.772(3) y | β− (98.62%) | 227Th | 3/2− | Trace [n 11] | ||||||||||
α (1.38%) | 223Fr | ||||||||||||||||||
228Ac | Mesothorium 2 | 89 | 139 | 228.0310211(27) | 6.13(2) h | β− | 228Th | 3+ | Trace [n 12] | ||||||||||
229Ac | 89 | 140 | 229.03302(4) | 62.7(5) min | β− | 229Th | (3/2+) | ||||||||||||
230Ac | 89 | 141 | 230.03629(32) | 122(3) s | β− | 230Th | (1+) | ||||||||||||
231Ac | 89 | 142 | 231.03856(11) | 7.5(1) min | β− | 231Th | (1/2+) | ||||||||||||
232Ac | 89 | 143 | 232.04203(11) | 119(5) s | β− | 232Th | (1+) | ||||||||||||
233Ac | 89 | 144 | 233.04455(32)# | 145(10) s | β− | 233Th | (1/2+) | ||||||||||||
234Ac | 89 | 145 | 234.04842(43)# | 44(7) s | β− | 234Th | |||||||||||||
235Ac | 89 | 146 | 235.05123(38)# | 60(4) s | β− | 235Th | 1/2+# | ||||||||||||
236Ac [6] | 89 | 147 | 236.05530(54)# | 72+345 −33 s |
β− | 236Th | |||||||||||||
This table header & footer: |
CD: | Cluster decay |
EC: | Electron capture |
IT: | Isomeric transition |
Actinides [7] by decay chain |
Half-life range ( a) |
Fission products of 235U by yield [8] | ||||||
---|---|---|---|---|---|---|---|---|
4n | 4n + 1 | 4n + 2 | 4n + 3 | 4.5–7% | 0.04–1.25% | <0.001% | ||
228Ra№ | 4–6 a | 155Euþ | ||||||
244Cmƒ | 241Puƒ | 250Cf | 227Ac№ | 10–29 a | 90Sr | 85Kr | 113mCdþ | |
232Uƒ | 238Puƒ | 243Cmƒ | 29–97 a | 137Cs | 151Smþ | 121mSn | ||
248Bk [9] | 249Cfƒ | 242mAmƒ | 141–351 a |
No fission products have a half-life | ||||
241Amƒ | 251Cfƒ [10] | 430–900 a | ||||||
226Ra№ | 247Bk | 1.3–1.6 ka | ||||||
240Pu | 229Th | 246Cmƒ | 243Amƒ | 4.7–7.4 ka | ||||
245Cmƒ | 250Cm | 8.3–8.5 ka | ||||||
239Puƒ | 24.1 ka | |||||||
230Th№ | 231Pa№ | 32–76 ka | ||||||
236Npƒ | 233Uƒ | 234U№ | 150–250 ka | 99Tc₡ | 126Sn | |||
248Cm | 242Pu | 327–375 ka | 79Se₡ | |||||
1.53 Ma | 93Zr | |||||||
237Npƒ | 2.1–6.5 Ma | 135Cs₡ | 107Pd | |||||
236U | 247Cmƒ | 15–24 Ma | 129I₡ | |||||
244Pu | 80 Ma |
... nor beyond 15.7 Ma [11] | ||||||
232Th№ | 238U№ | 235Uƒ№ | 0.7–14.1 Ga | |||||
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Actinium (89Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic weight cannot be given. There are 34 known isotopes, from 203Ac to 236Ac, and 7 isomers. Three isotopes are found in nature, 225Ac, 227Ac and 228Ac, as intermediate decay products of, respectively, 237Np, 235U, and 232Th. 228Ac and 225Ac are extremely rare, so almost all natural actinium is 227Ac.
The most stable isotopes are 227Ac with a half-life of 21.772 years, 225Ac with a half-life of 10.0 days, and 226Ac with a half-life of 29.37 hours. All other isotopes have half-lives under 10 hours, and most under a minute. The shortest-lived known isotope is 217Ac with a half-life of 69 ns.
Purified 227Ac comes into equilibrium with its decay products (227Th and 223Fr) after 185 days. [2]
Nuclide [n 1] |
Historic name |
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] | |||||||||||||||||||
203Ac [3] | 89 | 114 | 56+269 −26 μs |
α | 199Fr | (1/2+) | |||||||||||||
204Ac [4] | 89 | 115 | 7.4+2.2 −1.4 ms |
α | 200Fr | ||||||||||||||
205Ac [5] | 89 | 116 | 7.7+2.7 −1.6 ms [4] |
α | 201Fr | 9/2−? | |||||||||||||
206Ac | 89 | 117 | 206.01450(8) | 25(7) ms | α | 202Fr | (3+) | ||||||||||||
206m1Ac | 80(50) keV | 15(6) ms | α | 202Fr | |||||||||||||||
206m2Ac | 290(110)# keV | 41(16) ms | α | 202mFr | (10−) | ||||||||||||||
207Ac | 89 | 118 | 207.01195(6) | 31(8) ms [27(+11−6) ms] |
α | 203Fr | 9/2−# | ||||||||||||
208Ac | 89 | 119 | 208.01155(6) | 97(16) ms [95(+24−16) ms] |
α (99%) | 204Fr | (3+) | ||||||||||||
β+ (1%) | 208Ra | ||||||||||||||||||
208mAc | 506(26) keV | 28(7) ms [25(+9−5) ms] |
α (89%) | 204Fr | (10−) | ||||||||||||||
IT (10%) | 208Ac | ||||||||||||||||||
β+ (1%) | 208Ra | ||||||||||||||||||
209Ac | 89 | 120 | 209.00949(5) | 92(11) ms | α (99%) | 205Fr | (9/2−) | ||||||||||||
β+ (1%) | 209Ra | ||||||||||||||||||
210Ac | 89 | 121 | 210.00944(6) | 350(40) ms | α (96%) | 206Fr | 7+# | ||||||||||||
β+ (4%) | 210Ra | ||||||||||||||||||
211Ac | 89 | 122 | 211.00773(8) | 213(25) ms | α (99.8%) | 207Fr | 9/2−# | ||||||||||||
β+ (.2%) | 211Ra | ||||||||||||||||||
212Ac | 89 | 123 | 212.00781(7) | 920(50) ms | α (97%) | 208Fr | 6+# | ||||||||||||
β+ (3%) | 212Ra | ||||||||||||||||||
213Ac | 89 | 124 | 213.00661(6) | 731(17) ms | α | 209Fr | (9/2−)# | ||||||||||||
β+ (rare) | 213Ra | ||||||||||||||||||
214Ac | 89 | 125 | 214.006902(24) | 8.2(2) s | α (89%) | 210Fr | (5+)# | ||||||||||||
β+ (11%) | 214Ra | ||||||||||||||||||
215Ac | 89 | 126 | 215.006454(23) | 0.17(1) s | α (99.91%) | 211Fr | 9/2− | ||||||||||||
β+ (.09%) | 215Ra | ||||||||||||||||||
216Ac | 89 | 127 | 216.008720(29) | 0.440(16) ms | α | 212Fr | (1−) | ||||||||||||
β+ (7×10−5%) | 216Ra | ||||||||||||||||||
216mAc | 44(7) keV | 443(7) µs | α | 212Fr | (9−) | ||||||||||||||
217Ac | 89 | 128 | 217.009347(14) | 69(4) ns | α | 213Fr | 9/2− | ||||||||||||
β+ (6.9×10−9%) | 217Ra | ||||||||||||||||||
217mAc | 2012(20) keV | 740(40) ns | (29/2)+ | ||||||||||||||||
218Ac | 89 | 129 | 218.01164(5) | 1.08(9) µs | α | 214Fr | (1−)# | ||||||||||||
218mAc | 584(50)# keV | 103(11) ns | (11+) | ||||||||||||||||
219Ac | 89 | 130 | 219.01242(5) | 11.8(15) µs | α | 215Fr | 9/2− | ||||||||||||
β+ (10−6%) | 219Ra | ||||||||||||||||||
220Ac | 89 | 131 | 220.014763(16) | 26.36(19) ms | α | 216Fr | (3−) | ||||||||||||
β+ (5×10−4%) | 220Ra | ||||||||||||||||||
221Ac | 89 | 132 | 221.01559(5) | 52(2) ms | α | 217Fr | 9/2−# | ||||||||||||
222Ac | 89 | 133 | 222.017844(6) | 5.0(5) s | α (99%) | 218Fr | 1− | ||||||||||||
β+ (1%) | 222Ra | ||||||||||||||||||
222mAc | 200(150)# keV | 1.05(7) min | α (88.6%) | 218Fr | high | ||||||||||||||
IT (10%) | 222Ac | ||||||||||||||||||
β+ (1.4%) | 222Ra | ||||||||||||||||||
223Ac | 89 | 134 | 223.019137(8) | 2.10(5) min | α (99%) | 219Fr | (5/2−) | ||||||||||||
EC (1%) | 223Ra | ||||||||||||||||||
CD (3.2×10−9%) | 209Bi 14C | ||||||||||||||||||
224Ac | 89 | 135 | 224.021723(4) | 2.78(17) h | β+ (90.9%) | 224Ra | 0− | ||||||||||||
α (9.1%) | 220Fr | ||||||||||||||||||
β− (1.6%) | 224Th | ||||||||||||||||||
225Ac [n 8] | 89 | 136 | 225.023230(5) | 10.0(1) d | α | 221Fr | (3/2−) | Trace [n 9] | |||||||||||
CD (6×10−10%) | 211Bi 14C | ||||||||||||||||||
226Ac | 89 | 137 | 226.026098(4) | 29.37(12) h | β− (83%) | 226Th | (1)(−#) | ||||||||||||
EC (17%) | 226Ra | ||||||||||||||||||
α (.006%) | 222Fr | ||||||||||||||||||
227Ac | Actinium [n 10] | 89 | 138 | 227.0277521(26) | 21.772(3) y | β− (98.62%) | 227Th | 3/2− | Trace [n 11] | ||||||||||
α (1.38%) | 223Fr | ||||||||||||||||||
228Ac | Mesothorium 2 | 89 | 139 | 228.0310211(27) | 6.13(2) h | β− | 228Th | 3+ | Trace [n 12] | ||||||||||
229Ac | 89 | 140 | 229.03302(4) | 62.7(5) min | β− | 229Th | (3/2+) | ||||||||||||
230Ac | 89 | 141 | 230.03629(32) | 122(3) s | β− | 230Th | (1+) | ||||||||||||
231Ac | 89 | 142 | 231.03856(11) | 7.5(1) min | β− | 231Th | (1/2+) | ||||||||||||
232Ac | 89 | 143 | 232.04203(11) | 119(5) s | β− | 232Th | (1+) | ||||||||||||
233Ac | 89 | 144 | 233.04455(32)# | 145(10) s | β− | 233Th | (1/2+) | ||||||||||||
234Ac | 89 | 145 | 234.04842(43)# | 44(7) s | β− | 234Th | |||||||||||||
235Ac | 89 | 146 | 235.05123(38)# | 60(4) s | β− | 235Th | 1/2+# | ||||||||||||
236Ac [6] | 89 | 147 | 236.05530(54)# | 72+345 −33 s |
β− | 236Th | |||||||||||||
This table header & footer: |
CD: | Cluster decay |
EC: | Electron capture |
IT: | Isomeric transition |
Actinides [7] by decay chain |
Half-life range ( a) |
Fission products of 235U by yield [8] | ||||||
---|---|---|---|---|---|---|---|---|
4n | 4n + 1 | 4n + 2 | 4n + 3 | 4.5–7% | 0.04–1.25% | <0.001% | ||
228Ra№ | 4–6 a | 155Euþ | ||||||
244Cmƒ | 241Puƒ | 250Cf | 227Ac№ | 10–29 a | 90Sr | 85Kr | 113mCdþ | |
232Uƒ | 238Puƒ | 243Cmƒ | 29–97 a | 137Cs | 151Smþ | 121mSn | ||
248Bk [9] | 249Cfƒ | 242mAmƒ | 141–351 a |
No fission products have a half-life | ||||
241Amƒ | 251Cfƒ [10] | 430–900 a | ||||||
226Ra№ | 247Bk | 1.3–1.6 ka | ||||||
240Pu | 229Th | 246Cmƒ | 243Amƒ | 4.7–7.4 ka | ||||
245Cmƒ | 250Cm | 8.3–8.5 ka | ||||||
239Puƒ | 24.1 ka | |||||||
230Th№ | 231Pa№ | 32–76 ka | ||||||
236Npƒ | 233Uƒ | 234U№ | 150–250 ka | 99Tc₡ | 126Sn | |||
248Cm | 242Pu | 327–375 ka | 79Se₡ | |||||
1.53 Ma | 93Zr | |||||||
237Npƒ | 2.1–6.5 Ma | 135Cs₡ | 107Pd | |||||
236U | 247Cmƒ | 15–24 Ma | 129I₡ | |||||
244Pu | 80 Ma |
... nor beyond 15.7 Ma [11] | ||||||
232Th№ | 238U№ | 235Uƒ№ | 0.7–14.1 Ga | |||||
|