Isotopes of actinium

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.

List of isotopes

 * 203Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 114
 * α
 * 199Fr
 * (1/2+)
 * 204Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 115
 * α
 * 200Fr
 * 205Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 116
 * α
 * 201Fr
 * 9/2−?
 * 206Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 117
 * 206.01450(8)
 * 25(7) ms
 * α
 * 202Fr
 * (3+)
 * style="text-indent:1em" | 206m1Ac
 * colspan="3" style="text-indent:2em" | 80(50) keV
 * 15(6) ms
 * α
 * 202Fr
 * style="text-indent:1em" | 206m2Ac
 * colspan="3" style="text-indent:2em" | 290(110)# keV
 * 41(16) ms
 * α
 * 202mFr
 * (10−)
 * 207Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 118
 * 207.01195(6)
 * 31(8) ms [27(+11−6) ms]
 * α
 * 203Fr
 * 9/2−#
 * rowspan=2|208Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 119
 * rowspan=2|208.01155(6)
 * rowspan=2|97(16) ms [95(+24−16) ms]
 * α (99%)
 * 204Fr
 * rowspan=2|(3+)
 * rowspan=2|
 * β+ (1%)
 * 208Ra
 * rowspan=3 style="text-indent:1em" | 208mAc
 * rowspan=3|
 * rowspan=3 colspan="3" style="text-indent:2em" | 506(26) keV
 * rowspan=3|28(7) ms [25(+9−5) ms]
 * α (89%)
 * 204Fr
 * rowspan=3|(10−)
 * rowspan=3|
 * IT (10%)
 * 208Ac
 * β+ (1%)
 * 208Ra
 * rowspan=2|209Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 120
 * rowspan=2|209.00949(5)
 * rowspan=2|92(11) ms
 * α (99%)
 * 205Fr
 * rowspan=2|(9/2−)
 * rowspan=2|
 * β+ (1%)
 * 209Ra
 * rowspan=2|210Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 121
 * rowspan=2|210.00944(6)
 * rowspan=2|350(40) ms
 * α (96%)
 * 206Fr
 * rowspan=2|7+#
 * rowspan=2|
 * β+ (4%)
 * 210Ra
 * rowspan=2|211Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 122
 * rowspan=2|211.00773(8)
 * rowspan=2|213(25) ms
 * α (99.8%)
 * 207Fr
 * rowspan=2|9/2−#
 * rowspan=2|
 * β+ (.2%)
 * 211Ra
 * rowspan=2|212Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 123
 * rowspan=2|212.00781(7)
 * rowspan=2|920(50) ms
 * α (97%)
 * 208Fr
 * rowspan=2|6+#
 * rowspan=2|
 * β+ (3%)
 * 212Ra
 * rowspan=2|213Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 124
 * rowspan=2|213.00661(6)
 * rowspan=2|731(17) ms
 * α
 * 209Fr
 * rowspan=2|(9/2−)#
 * rowspan=2|
 * β+ (rare)
 * 213Ra
 * rowspan=2|214Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 125
 * rowspan=2|214.006902(24)
 * rowspan=2|8.2(2) s
 * α (89%)
 * 210Fr
 * rowspan=2|(5+)#
 * rowspan=2|
 * β+ (11%)
 * 214Ra
 * rowspan=2|215Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 126
 * rowspan=2|215.006454(23)
 * rowspan=2|0.17(1) s
 * α (99.91%)
 * 211Fr
 * rowspan=2|9/2−
 * rowspan=2|
 * β+ (.09%)
 * 215Ra
 * rowspan=2|216Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 127
 * rowspan=2|216.008720(29)
 * rowspan=2|0.440(16) ms
 * α
 * 212Fr
 * rowspan=2|(1−)
 * rowspan=2|
 * β+ (7×10−5%)
 * 216Ra
 * style="text-indent:1em" | 216mAc
 * colspan="3" style="text-indent:2em" | 44(7) keV
 * 443(7) μs
 * α
 * 212Fr
 * (9−)
 * rowspan=2|217Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 128
 * rowspan=2|217.009347(14)
 * rowspan=2|69(4) ns
 * α
 * 213Fr
 * rowspan=2|9/2−
 * rowspan=2|
 * β+ (6.9×10−9%)
 * 217Ra
 * style="text-indent:1em" | 217mAc
 * colspan="3" style="text-indent:2em" | 2012(20) keV
 * 740(40) ns
 * (29/2)+
 * 218Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 129
 * 218.01164(5)
 * 1.08(9) μs
 * α
 * 214Fr
 * (1−)#
 * style="text-indent:1em" | 218mAc
 * colspan="3" style="text-indent:2em" | 584(50)# keV
 * 103(11) ns
 * (11+)
 * rowspan=2|219Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 130
 * rowspan=2|219.01242(5)
 * rowspan=2|11.8(15) μs
 * α
 * 215Fr
 * rowspan=2|9/2−
 * rowspan=2|
 * β+ (10−6%)
 * 219Ra
 * rowspan=2|220Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 131
 * rowspan=2|220.014763(16)
 * rowspan=2|26.36(19) ms
 * α
 * 216Fr
 * rowspan=2|(3−)
 * rowspan=2|
 * β+ (5×10−4%)
 * 220Ra
 * 221Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 132
 * 221.01559(5)
 * 52(2) ms
 * α
 * 217Fr
 * 9/2−#
 * rowspan=2|222Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 133
 * rowspan=2|222.017844(6)
 * rowspan=2|5.0(5) s
 * α (99%)
 * 218Fr
 * rowspan=2|1−
 * rowspan=2|
 * β+ (1%)
 * 222Ra
 * rowspan=3 style="text-indent:1em" | 222mAc
 * rowspan=3|
 * rowspan=3 colspan="3" style="text-indent:2em" | 200(150)# keV
 * rowspan=3|1.05(7) min
 * α (88.6%)
 * 218Fr
 * rowspan=3|high
 * rowspan=3|
 * IT (10%)
 * 222Ac
 * β+ (1.4%)
 * 222Ra
 * rowspan=3|223Ac
 * rowspan=3|
 * rowspan=3 style="text-align:right" | 89
 * rowspan=3 style="text-align:right" | 134
 * rowspan=3|223.019137(8)
 * rowspan=3|2.10(5) min
 * α (99%)
 * 219Fr
 * rowspan=3|(5/2−)
 * rowspan=3|
 * EC (1%)
 * 223Ra
 * CD (3.2×10−9%)
 * 209Bi 14C
 * rowspan=3|224Ac
 * rowspan=3|
 * rowspan=3 style="text-align:right" | 89
 * rowspan=3 style="text-align:right" | 135
 * rowspan=3|224.021723(4)
 * rowspan=3|2.78(17) h
 * β+ (90.9%)
 * 224Ra
 * rowspan=3|0−
 * rowspan=3|
 * α (9.1%)
 * 220Fr
 * β− (1.6%)
 * 224Th
 * rowspan=2|225Ac
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 136
 * rowspan=2|225.023230(5)
 * rowspan=2|10.0(1) d
 * α
 * 221Fr
 * rowspan=2|(3/2−)
 * rowspan=2|Trace
 * CD (6×10−10%)
 * 211Bi 14C
 * rowspan=3|226Ac
 * rowspan=3|
 * rowspan=3 style="text-align:right" | 89
 * rowspan=3 style="text-align:right" | 137
 * rowspan=3|226.026098(4)
 * rowspan=3|29.37(12) h
 * β− (83%)
 * 226Th
 * rowspan=3|(1)(−#)
 * rowspan=3|
 * EC (17%)
 * 226Ra
 * α (.006%)
 * 222Fr
 * rowspan=2|227Ac
 * rowspan=2|Actinium
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 138
 * rowspan=2|227.0277521(26)
 * rowspan=2|21.772(3) y
 * β− (98.62%)
 * 227Th
 * rowspan=2|3/2−
 * rowspan=2|Trace
 * α (1.38%)
 * 223Fr
 * 228Ac
 * Mesothorium 2
 * style="text-align:right" | 89
 * style="text-align:right" | 139
 * 228.0310211(27)
 * 6.13(2) h
 * β−
 * 228Th
 * 3+
 * Trace
 * 229Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 140
 * 229.03302(4)
 * 62.7(5) min
 * β−
 * 229Th
 * (3/2+)
 * 230Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 141
 * 230.03629(32)
 * 122(3) s
 * β−
 * 230Th
 * (1+)
 * 231Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 142
 * 231.03856(11)
 * 7.5(1) min
 * β−
 * 231Th
 * (1/2+)
 * 232Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 143
 * 232.04203(11)
 * 119(5) s
 * β−
 * 232Th
 * (1+)
 * 233Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 144
 * 233.04455(32)#
 * 145(10) s
 * β−
 * 233Th
 * (1/2+)
 * 234Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 145
 * 234.04842(43)#
 * 44(7) s
 * β−
 * 234Th
 * 235Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 146
 * 235.05123(38)#
 * 60(4) s
 * β−
 * 235Th
 * 1/2+#
 * 236Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 147
 * 236.05530(54)#
 * β−
 * 236Th
 * rowspan=3|(1)(−#)
 * rowspan=3|
 * EC (17%)
 * 226Ra
 * α (.006%)
 * 222Fr
 * rowspan=2|227Ac
 * rowspan=2|Actinium
 * rowspan=2 style="text-align:right" | 89
 * rowspan=2 style="text-align:right" | 138
 * rowspan=2|227.0277521(26)
 * rowspan=2|21.772(3) y
 * β− (98.62%)
 * 227Th
 * rowspan=2|3/2−
 * rowspan=2|Trace
 * α (1.38%)
 * 223Fr
 * 228Ac
 * Mesothorium 2
 * style="text-align:right" | 89
 * style="text-align:right" | 139
 * 228.0310211(27)
 * 6.13(2) h
 * β−
 * 228Th
 * 3+
 * Trace
 * 229Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 140
 * 229.03302(4)
 * 62.7(5) min
 * β−
 * 229Th
 * (3/2+)
 * 230Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 141
 * 230.03629(32)
 * 122(3) s
 * β−
 * 230Th
 * (1+)
 * 231Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 142
 * 231.03856(11)
 * 7.5(1) min
 * β−
 * 231Th
 * (1/2+)
 * 232Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 143
 * 232.04203(11)
 * 119(5) s
 * β−
 * 232Th
 * (1+)
 * 233Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 144
 * 233.04455(32)#
 * 145(10) s
 * β−
 * 233Th
 * (1/2+)
 * 234Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 145
 * 234.04842(43)#
 * 44(7) s
 * β−
 * 234Th
 * 235Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 146
 * 235.05123(38)#
 * 60(4) s
 * β−
 * 235Th
 * 1/2+#
 * 236Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 147
 * 236.05530(54)#
 * β−
 * 236Th
 * 234Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 145
 * 234.04842(43)#
 * 44(7) s
 * β−
 * 234Th
 * 235Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 146
 * 235.05123(38)#
 * 60(4) s
 * β−
 * 235Th
 * 1/2+#
 * 236Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 147
 * 236.05530(54)#
 * β−
 * 236Th
 * 236Ac
 * style="text-align:right" | 89
 * style="text-align:right" | 147
 * 236.05530(54)#
 * β−
 * 236Th
 * β−
 * 236Th
 * 236Th