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]
List of isotopes
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: |
- mAc – 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:
CD: Cluster 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.
- # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- Source of element's name
- Intermediate decay product of 235U
Actinides vs fission products
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 | |||||
|
Notable isotopes
Actinium-225
225Ac is a highly radioactive isotope with 136 neutrons. It has a half-life of 9.919 days. As of 2024, it is being researched as a possible alpha source in targeted alpha therapy.[12][13][14] It quickly decays, emitting three alpha particles in an average of less than ten days, into 213Bi, which itself is used as an alpha source.[15] Another benefit is that the decay chain of 225Ac ends in the nuclide 209Bi[note 1], which has a considerably shorter biological half-life than lead.[16][17] However, a major factor limiting its usage is the difficulty in producing the short-lived isotope, as it is most commonly isolated from aging parent nuclides (such as 233U); it may also be produced in cyclotrons, linear accelerators, or fast breeder reactors.[18]
Notes
- Bismuth-209 decays into thallium-205 with a half-life exceeding 1019 years, but this half-life is so long that for practical purposes bismuth-209 can be considered stable.