Actinium (Ac) has no stable isotopes, thus a standard atomic mass cannot be given. There are 31 known isotopes, from 206Ac to 236Ac, and 2 isomers. Two isotopes are found in nature, 227Ac and 228Ac, as intermediate decay products of, respectively, 235U and 232Th. 228Ac is extremely rare, and 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. Actinium also has two meta states.
Purified 227Ac comes into equilibrium with its decay products (227Th and 223Fr) after 185 days.[1]
Contents |
nuclide symbol |
historic name |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s)[2][n 1] |
daughter isotope(s)[n 2] |
nuclear spin |
representative isotopic composition (mole fraction) |
range of natural variation (mole fraction) |
---|---|---|---|---|---|---|---|---|---|---|
excitation energy | ||||||||||
206Ac | 89 | 117 | 206.01450(8) | 25(7) ms | (3+) | |||||
206m1Ac | 80(50) keV | 15(6) ms | ||||||||
206m2Ac | 290(110)# keV | 41(16) ms | (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 | (9-) | |||||||
217Ac | 89 | 128 | 217.009347(14) | 69(4) ns | α (98%) | 213Fr | 9/2- | |||
β+ (2%) | 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 3] | 89 | 136 | 225.023230(5) | 10.0(1) d | α | 221Fr | (3/2-) | |||
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 4] | 89 | 138 | 227.0277521(26) | 21.772(3) a | β- (98.61%) | 227Th | 3/2- | Trace[n 5] | |
α (1.38%) | 223Fr | |||||||||
228Ac | Mesothorium 2 | 89 | 139 | 228.0310211(27) | 6.15(2) h | β- | 228Th | 3+ | Trace[n 6] | |
α (5.5×10−6%) | 224Fr | |||||||||
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)# | 40# s | β- | 235Th | 1/2+# | |||
236Ac | 89 | 147 | 236.05530(54)# | 2# min | β- | 236Th |
Book: Actinium | |
Wikipedia books are collections of articles that can be downloaded or ordered in print. |
Isotopes of radium | Isotopes of actinium | Isotopes of thorium |
Index to isotope pages · Table of nuclides |