View source for Isotopes of actinium

{{Short description|none}}
{{Infobox actinium isotopes}}
[[Actinium]] (<sub>89</sub>Ac) has no stable [[isotope]]s and no characteristic terrestrial isotopic composition, thus a [[standard atomic weight]] cannot be given. There are 34 known isotopes, from <sup>203</sup>Ac to <sup>236</sup>Ac, and 7 [[nuclear isomer|isomers]]. Three isotopes are found in nature, [[actinium-225|<sup>225</sup>Ac]], <sup>227</sup>Ac and <sup>228</sup>Ac, as intermediate decay products of, respectively, [[Neptunium-237|<sup>237</sup>Np]], [[Uranium-235|<sup>235</sup>U]], and [[Thorium-232|<sup>232</sup>Th]]. <sup>228</sup>Ac and <sup>225</sup>Ac are extremely rare, so almost all natural actinium is <sup>227</sup>Ac.

The most stable isotopes are <sup>227</sup>Ac with a half-life of 21.772 years, <sup>225</sup>Ac with a half-life of 10.0 days, and <sup>226</sup>Ac 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 <sup>217</sup>Ac with a half-life of 69 [[nanosecond|ns]].

Purified <sup>227</sup>Ac comes into equilibrium with its decay products (<sup>227</sup>Th and <sup>223</sup>Fr) after 185 days.<ref name="nostrand332">
{{cite book
 | year = 2005
 | chapter = Chemical Elements
 | title = Van Nostrand's Encyclopedia of Chemistry
 | editor = G. D. Considine
 | page = 332
 | publisher = [[Wiley-Interscience]]
 | isbn = 978-0-471-61525-5
}}</ref>

== List of isotopes ==
{{Anchor|Actinium-206m|Actinium-215m1|Actinium-215m2|Actinium-216m1|Actinium-216m2|Actinium-218m1|Actinium-218m2|Actinium-228m|Actinium-234m1|Actinium-234m2|Actinium-237}}

<!--Please delete anchor(s) from the list above or table below if adding a dedicated isotope section(s).-->

{{Isotopes table
|symbol=Ac
|refs=<!-- not NUBASE2016 yet -->
|notes=m, histname, unc(), mass#, exen#, spin(), spin#, daughter-nst, CD, EC, IT
}}
|-id=Actinium-203
| <sup>203</sup>Ac<ref name="203Ac">{{cite journal |last1=Wang |first1=J. G. |last2=Gan |first2=Z. G. |last3=Zhang |first3=Z. Y. |last4=Huang |first4=M. H. |last5=Ma |first5=L. |last6=Zhang |first6=M. M. |last7=Yang |first7=H. B. |last8=Yang |first8=C. L. |last9=Qiang |first9=Y. H. |last10=Huang |first10=X. Y. |last11=Zhao |first11=Z. |last12=Xu |first12=S. Y. |last13=Li |first13=Z. C. |last14=Chen |first14=L. X. |last15=Sun |first15=L. C. |last16=Zhou |first16=H. |last17=Zhang |first17=X. |last18=Wu |first18=X. L. |last19=Tian |first19=Y. L. |last20=Wang |first20=Y. S. |last21=Wang |first21=J. Y. |last22=Huang |first22=W. X. |last23=Liu |first23=M. L. |last24=Lu |first24=Z. W. |last25=He |first25=Y. |last26=Ren |first26=Z. Z. |last27=Zhou |first27=S. G. |last28=Zhou |first28=X. H. |last29=Xu |first29=H. S. |last30=Utyonkov |first30=V. K. |last31=Voinov |first31=A. A. |last32=Tsyganov |first32=Yu. S. |last33=Polyakov |first33=A. N. |display-authors=3 |title=α-decay properties of new neutron-deficient isotope 203Ac |journal=Physics Letters B |date=1 March 2024 |volume=850 |pages=138503 |doi=10.1016/j.physletb.2024.138503 |issn=0370-2693|doi-access=free }}</ref>
|
| style="text-align:right" | 89
| style="text-align:right" | 114
| 
| {{Val|56|269|26|u=μs}}
| [[alpha decay|α]]
| <sup>199</sup>Fr
| (1/2+)
|
|-id=Actinium-204
|<sup>204</sup>Ac<ref name="204Ac">{{cite journal |last1=Huang |first1=M. H. |last2=Gan |first2=Z. G. |last3=Zhang |first3=Z. Y. |last4=Ma |first4=L. |last5=Wang |first5=J. G. |last6=Zhang |first6=M. M. |last7=Yang |first7=H. B. |last8=Yang |first8=C. L. |last9=Huang |first9=X. Y. |last10=Zhao |first10=Z. |last11=Xu |first11=S. Y. |last12=Chen |first12=L. X. |last13=Wen |first13=X. J. |last14=Niu |first14=Y. F. |last15=Yuan |first15=C. X. |last16=Tian |first16=Y. L. |last17=Wang |first17=Y. S. |last18=Wang |first18=J. Y. |last19=Liu |first19=M. L. |last20=Qiang |first20=Y. H. |last21=Yang |first21=W. Q. |last22=Zhang |first22=H. B. |last23=Lu |first23=Z. W. |last24=Guo |first24=S. |last25=Huang |first25=W. X. |last26=He |first26=Y. |last27=Ren |first27=Z. Z. |last28=Zhou |first28=S. G. |last29=Zhou |first29=X. H. |last30=Xu |first30=H. S. |last31=Utyonkov |first31=V. K. |last32=Voinov |first32=A. A. |last33=Tsyganov |first33=Yu. S. |last34=Polyakov |first34=A. N. |display-authors=3 |title=α decay of the new isotope <sup>204</sup>Ac |journal=Physics Letters B |date=10 November 2022 |volume=834 |pages=137484 |doi=10.1016/j.physletb.2022.137484 |bibcode=2022PhLB..83437484H |s2cid=252730841 |language=en |issn=0370-2693|doi-access=free }}</ref>
|
| style="text-align:right" | 89
| style="text-align:right" | 115
|
| {{Val|7.4|2.2|1.4|u=ms}}
| α
| <sup>200</sup>Fr
|
|
|-id=Actinium-205
|<sup>205</sup>Ac<ref name="ZhangEtAl2014">{{Cite journal |last1 = Zhang |first1 = Z. Y. |last2 = Gan |first2 = Z. G. |last3=Ma |first3=L. |last4=Yu |first4=L. |last5=Yang |first5=H. B. |last6=Huang |first6=T. H. |last7=Li |first7=G. S. |last8=Tian |first8=Y. L. |last9=Wang |first9=Y. S. |last10=Xu |first10=X. X. |last11=Huang |first11=M. H. |last12=Luo |first12=C. |last13=Ren |first13=Z. Z. |last14=Zhou |first14=S.G. |last15=Zhou |first15=X. H. |last16=Xu |first16=H. S. |last17=Xiao |first17=G. Q. |display-authors=3 | title =α decay of the new neutron-deficient isotope <sup>205</sup>Ac| journal = Physical Review C | volume = 89 | issue = 1 | pages = 014308 |date=January 2014 | url = http://journals.aps.org/prc/abstract/10.1103/PhysRevC.89.014308 | doi =10.1103/PhysRevC.89.014308|bibcode=2014PhRvC..89a4308Z }}</ref>
|
| style="text-align:right" | 89
| style="text-align:right" | 116
|
| {{val|7.7|2.7|1.6|u=ms}}<ref name="204Ac"/>
| α
| <sup>201</sup>Fr
| 9/2−?
|
|-id=Actinium-206
| <sup>206</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 117
| 206.01450(8)
| 25(7)&nbsp;ms
| α
| <sup>202</sup>Fr
| (3+)
|
|-id=Actinium-206m1
| style="text-indent:1em" | <sup>206m1</sup>Ac
|
| colspan="3" style="text-indent:2em" | 80(50) keV
| 15(6)&nbsp;ms
| α
| <sup>202</sup>Fr
|
|
|-id=Actinium-206m2
| style="text-indent:1em" | <sup>206m2</sup>Ac
|
| colspan="3" style="text-indent:2em" | 290(110)# keV
| 41(16)&nbsp;ms
| α
| <sup>202m</sup>Fr
| (10−)
|
|-id=Actinium-207
| <sup>207</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 118
| 207.01195(6)
| 31(8)&nbsp;ms<br/>[27(+11−6)&nbsp;ms]
| α
| <sup>203</sup>Fr
| 9/2−#
|
|-id=Actinium-208
| rowspan=2|<sup>208</sup>Ac
| 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)&nbsp;ms<br/>[95(+24−16)&nbsp;ms]
| α (99%)
| <sup>204</sup>Fr
| rowspan=2|(3+)
| rowspan=2|
|-
| β<sup>+</sup> (1%)
| <sup>208</sup>Ra
|-id=Actinium-208m
| rowspan=3 style="text-indent:1em" | <sup>208m</sup>Ac
| rowspan=3|
| rowspan=3 colspan="3" style="text-indent:2em" | 506(26) keV
| rowspan=3|28(7)&nbsp;ms<br/>[25(+9−5)&nbsp;ms]
| α (89%)
| <sup>204</sup>Fr
| rowspan=3|(10−)
| rowspan=3|
|-
| [[Isomeric transition|IT]] (10%)
| <sup>208</sup>Ac
|-
| β<sup>+</sup> (1%)
| <sup>208</sup>Ra
|-id=Actinium-209
| rowspan=2|<sup>209</sup>Ac
| 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)&nbsp;ms
| α (99%)
| <sup>205</sup>Fr
| rowspan=2|(9/2−)
| rowspan=2|
|-
| β<sup>+</sup> (1%)
| <sup>209</sup>Ra
|-id=Actinium-210
| rowspan=2|<sup>210</sup>Ac
| 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)&nbsp;ms
| α (96%)
| <sup>206</sup>Fr
| rowspan=2|7+#
| rowspan=2|
|-
| β<sup>+</sup> (4%)
| <sup>210</sup>Ra
|-id=Actinium-211
| rowspan=2|<sup>211</sup>Ac
| 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)&nbsp;ms
| α (99.8%)
| <sup>207</sup>Fr
| rowspan=2|9/2−#
| rowspan=2| 
|-
| β<sup>+</sup> (.2%)
| <sup>211</sup>Ra
|-id=Actinium-212
| rowspan=2|<sup>212</sup>Ac
| 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)&nbsp;ms
| α (97%)
| <sup>208</sup>Fr
| rowspan=2|6+#
| rowspan=2|
|-
| β<sup>+</sup> (3%)
| <sup>212</sup>Ra
|-id=Actinium-213
| rowspan=2|<sup>213</sup>Ac
| 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)&nbsp;ms
| α
| <sup>209</sup>Fr
| rowspan=2|(9/2−)#
| rowspan=2|
|-
| β<sup>+</sup> (rare)
| <sup>213</sup>Ra
|-id=Actinium-214
| rowspan=2|<sup>214</sup>Ac
| 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)&nbsp;s
| α (89%)
| <sup>210</sup>Fr
| rowspan=2|(5+)#
| rowspan=2|
|-
| β<sup>+</sup> (11%)
| <sup>214</sup>Ra
|-id=Actinium-215
| rowspan=2|<sup>215</sup>Ac
| 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)&nbsp;s
| α (99.91%)
| <sup>211</sup>Fr
| rowspan=2|9/2−
| rowspan=2|
|-
| β<sup>+</sup> (.09%)
| <sup>215</sup>Ra
|-id=Actinium-216
| <sup>216</sup>Ac
| 
| style="text-align:right" | 89
| style="text-align:right" | 127
| 216.008720(29)
| 440(16)&nbsp;μs
| α
| <sup>212</sup>Fr
| (1−)
| 
|-id=Actinium-216m1
| style="text-indent:1em" | <sup>216m1</sup>Ac
|
| colspan="3" style="text-indent:2em" | 38(5) keV
| 441(7)&nbsp;μs
| α
| <sup>212</sup>Fr
| (9−)
|
|-id=Actinium-216m2
| style="text-indent:1em" | <sup>216m2</sup>Ac
|
| colspan="3" style="text-indent:2em" | 422#(100#) keV
| ~300&nbsp;ns
| IT
| <sup>216</sup>Ac
| 
|
|-id=Actinium-217
| <sup>217</sup>Ac
| 
| style="text-align:right" | 89
| style="text-align:right" | 128
| 217.009347(14)
| 69(4)&nbsp;ns
| α
| <sup>213</sup>Fr
| 9/2−
| 
|-id=Actinium-217m
| style="text-indent:1em" | <sup>217m</sup>Ac
|
| colspan="3" style="text-indent:2em" | 2012(20) keV
| 740(40)&nbsp;ns
|
|
| (29/2)+
|
|-id=Actinium-218
| <sup>218</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 129
| 218.01164(5)
| 1.08(9)&nbsp;μs
| α
| <sup>214</sup>Fr
| (1−)#
|
|-id=Actinium-218m
| style="text-indent:1em" | <sup>218m</sup>Ac
|
| colspan="3" style="text-indent:2em" | 607(86)# keV
| 103(11)&nbsp;ns
| IT
| <sup>218</sup>Ac
| (11+)
|
|-id=Actinium-219
| <sup>219</sup>Ac
| 
| style="text-align:right" | 89
| style="text-align:right" | 130
| 219.01242(5)
| 11.8(15)&nbsp;μs
| α
| <sup>215</sup>Fr
| 9/2−
| 
|-id=Actinium-220
| <sup>220</sup>Ac
| 
| style="text-align:right" | 89
| style="text-align:right" | 131
| 220.014763(16)
| 26.36(19)&nbsp;ms
| α
| <sup>216</sup>Fr
| (3−)
| 
|-id=Actinium-221
| <sup>221</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 132
| 221.01559(5)
| 52(2)&nbsp;ms
| α
| <sup>217</sup>Fr
| 9/2−#
|
|-id=Actinium-222
| rowspan=2|<sup>222</sup>Ac
| 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)&nbsp;s
| α (99(1)%)
| <sup>218</sup>Fr
| rowspan=2|1−
| rowspan=2|
|-
| β<sup>+</sup> (1(1)%){{r|g=n|r=This decay mode has been observed, but only an upper limit of branching ratio is experimentally known{{NUBASE2020|ref}}}}
| <sup>222</sup>Ra
|-id=Actinium-222m
| rowspan=3 style="text-indent:1em" | <sup>222m</sup>Ac
| rowspan=3|
| rowspan=3 colspan="3" style="text-indent:2em" | 78(21) keV
| rowspan=3|1.05(5)&nbsp;min
| α (98.6%)
| <sup>218</sup>Fr
| rowspan=3|5+#
| rowspan=3|
|-
| β<sup>+</sup> (1.4%)
| <sup>222</sup>Ra
|-
| IT?
| <sup>222</sup>Ac
|-id=Actinium-223
| rowspan=3|<sup>223</sup>Ac
| 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)&nbsp;min
| α (99%)
| <sup>219</sup>Fr
| rowspan=3|(5/2−)
| rowspan=3|
|-
| [[Electron capture|EC]] (1%)
| <sup>223</sup>Ra
|-
| [[Cluster decay|CD]] (3.2×10<sup>−9</sup>%)
| '''''<sup>209</sup>Bi'''''<br/>[[Carbon-14|<sup>14</sup>C]]
|-id=Actinium-224
| rowspan=3|<sup>224</sup>Ac
| 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)&nbsp;h
| β<sup>+</sup> (90.9%)
| <sup>224</sup>Ra
| rowspan=3|0−
| rowspan=3|
|-
| α (9.1%)
| <sup>220</sup>Fr
|-
| β<sup>−</sup> (1.6%)
| <sup>224</sup>Th
|-
| rowspan=2|[[actinium-225|<sup>225</sup>Ac]]<ref group="n">Has [[Nuclear medicine|medical uses]]</ref>
| 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)&nbsp;d
| α
| <sup>221</sup>Fr
| rowspan=2|(3/2−)
| rowspan=2|Trace<ref group=n>Intermediate decay product of [[neptunium-237|<sup>237</sup>Np]]</ref>
|-
| CD (6×10<sup>−10</sup>%)
| <sup>211</sup>Bi<br/><sup>14</sup>C
|-
| rowspan=3|<sup>226</sup>Ac
| 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)&nbsp;h
| β<sup>−</sup> (83%)
| <sup>226</sup>Th
| rowspan=3|(1)(−#)
| rowspan=3|
|-
| EC (17%)
| <sup>226</sup>Ra
|-
| α (.006%)
| <sup>222</sup>Fr
|-
| rowspan=2|<sup>227</sup>Ac
| rowspan=2|Actinium<ref group="n">Source of element's name</ref>
| rowspan=2 style="text-align:right" | 89
| rowspan=2 style="text-align:right" | 138
| rowspan=2|227.0277521(26)
| rowspan=2|21.772(3)&nbsp;y
| β<sup>−</sup> (98.62%)
| <sup>227</sup>Th
| rowspan=2|3/2−
| rowspan=2|Trace<ref group="n">Intermediate [[decay product]] of [[Uranium-235|<sup>235</sup>U]]</ref>
|-
| α (1.38%)
| <sup>223</sup>Fr
|-id=Actinium-228
| <sup>228</sup>Ac
| Mesothorium 2
| style="text-align:right" | 89
| style="text-align:right" | 139
| 228.0310211(27)
| 6.13(2)&nbsp;h
| β<sup>−</sup>
| <sup>228</sup>Th
| 3+
| Trace<ref group="n">Intermediate decay product of [[thorium-232|<sup>232</sup>Th]]</ref>
|-id=Actinium-229
| <sup>229</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 140
| 229.03302(4)
| 62.7(5)&nbsp;min
| β<sup>−</sup>
| <sup>229</sup>Th
| (3/2+)
|
|-id=Actinium-230
| <sup>230</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 141
| 230.03629(32)
| 122(3)&nbsp;s
| β<sup>−</sup>
| <sup>230</sup>Th
| (1+)
|
|-id=Actinium-231
| <sup>231</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 142
| 231.03856(11)
| 7.5(1)&nbsp;min
| β<sup>−</sup>
| <sup>231</sup>Th
| (1/2+)
|
|-id=Actinium-232
| <sup>232</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 143
| 232.04203(11)
| 119(5)&nbsp;s
| β<sup>−</sup>
| '''''<sup>232</sup>Th'''''
| (1+)
|
|-id=Actinium-233
| <sup>233</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 144
| 233.04455(32)#
| 145(10)&nbsp;s
| β<sup>−</sup>
| <sup>233</sup>Th
| (1/2+)
|
|-id=Actinium-234
| <sup>234</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 145
| 234.04842(43)#
| 44(7)&nbsp;s
| β<sup>−</sup>
| <sup>234</sup>Th
|
|
|-id=Actinium-235
| <sup>235</sup>Ac
|
| style="text-align:right" | 89
| style="text-align:right" | 146
| 235.05123(38)#
| 60(4)&nbsp;s
| β<sup>−</sup>
| <sup>235</sup>Th
| 1/2+#
|
|-id=Actinium-236
| <sup>236</sup>Ac<ref name="236Ac-Chen">{{cite journal|last=Chen|first=L.|display-authors=etal|date=2010|title=Discovery and investigation of heavy neutron-rich isotopes with time-resolved Schottky spectrometry in the element range from thallium to actinium |url=http://epubs.surrey.ac.uk/7511/2/10_esr-trans-pb_plb_chen_preprint.pdf|journal=Physics Letters B|volume=691|issue=5|pages=234–237|doi=10.1016/j.physletb.2010.05.078|bibcode=2010PhLB..691..234C }}</ref>
|
| style="text-align:right" | 89
| style="text-align:right" | 147
| 236.05530(54)#
| {{val|72|345|33|u=s}}
| β<sup>−</sup>
| <sup>236</sup>Th
|
|
{{Isotopes table/footer}}

==Actinides vs fission products==
{{Actinides vs fission products}}
{{Clear}}

==Notable isotopes==
===Actinium-225===
{{main|Actinium-225}}
'''Actinium-225''' is a highly radioactive isotope with 136 neutrons. It is an [[alpha emitter]] and has a half-life of 9.919 days. As of 2024, it is being researched as a possible alpha source in [[targeted alpha therapy]].<ref>{{cite journal |last1=A. Scheinberg |first1=David |last2=R. McDevitt |first2=Michael |title=Actinium-225 in Targeted Alpha-Particle Therapeutic Applications |journal=Current Radiopharmaceuticals |date=1 October 2011 |volume=4 |issue=4 |pages=306–320 |doi=10.2174/1874471011104040306|pmid=22202153 |pmc=5565267 }}</ref><ref>{{cite journal |last1=Reissig |first1=Falco |last2=Bauer |first2=David |last3=Zarschler |first3=Kristof |last4=Novy |first4=Zbynek |last5=Bendova |first5=Katerina |last6=Ludik |first6=Marie-Charlotte |last7=Kopka |first7=Klaus |last8=Pietzsch |first8=Hans-Jürgen |last9=Petrik |first9=Milos |last10=Mamat |first10=Constantin |title=Towards Targeted Alpha Therapy with Actinium-225: Chelators for Mild Condition Radiolabeling and Targeting PSMA—A Proof of Concept Study |journal=Cancers |date=20 April 2021 |volume=13 |issue=8 |pages=1974 |doi=10.3390/cancers13081974|doi-access=free |pmid=33923965 |pmc=8073976 }}</ref><ref>{{cite journal |last1=Bidkar |first1=Anil P. |last2=Zerefa |first2=Luann |last3=Yadav |first3=Surekha |last4=VanBrocklin |first4=Henry F. |last5=Flavell |first5=Robert R. |title=Actinium-225 targeted alpha particle therapy for prostate cancer |journal=Theranostics |date=2024 |volume=14 |issue=7 |pages=2969–2992 |doi=10.7150/thno.96403}}</ref> Actinium-225 undergoes a series of three alpha decays – via the short-lived [[francium-221]] and [[astatine-217]] – to [[Isotopes_of_bismuth#Bismuth-213|<sup>213</sup>Bi]], which itself is used as an alpha source.<ref>{{cite journal |last1=Ahenkorah |first1=Stephen |last2=Cassells |first2=Irwin |last3=Deroose |first3=Christophe M. |last4=Cardinaels |first4=Thomas |last5=Burgoyne |first5=Andrew R. |last6=Bormans |first6=Guy |last7=Ooms |first7=Maarten |last8=Cleeren |first8=Frederik |title=Bismuth-213 for Targeted Radionuclide Therapy: From Atom to Bedside |journal=Pharmaceutics |date=21 April 2021 |volume=13 |issue=5 |pages=599 |doi=10.3390/pharmaceutics13050599|doi-access=free |pmc=8143329 }}</ref> Another benefit is that the decay chain of <sup>225</sup>Ac ends in the nuclide [[Bismuth-209|<sup>209</sup>Bi]],{{refn | group = note | Bismuth-209 decays into [[Isotopes of thallium | thallium-205]] with a half-life exceeding 10<sup>19</sup> years, but this half-life is so long that for practical purposes bismuth-209 can be considered stable.}} which has a considerably shorter biological half-life than lead.<ref>{{cite book |title=Handbook on the toxicology of metals. Volume 2: Specific metals |date=2015 |publisher=Elsevier, Aademic Press |location=Amsterdam Boston Heidelberg London |isbn=978-0-12-398293-3 |page=655 |edition=Fourth}}</ref><ref>{{cite journal |last1=Wani |first1=Ab Latif |last2=Ara |first2=Anjum |last3=Usmani |first3=Jawed Ahmad |title=Lead toxicity: a review |journal=Interdisciplinary Toxicology |date=1 June 2015 |volume=8 |issue=2 |pages=55–64 |doi=10.1515/intox-2015-0009|pmc=4961898 }}</ref> 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 [[Uranium-233|<sup>233</sup>U]]); it may also be produced in cyclotrons, linear accelerators, or fast [[breeder reactors]].<ref>{{cite journal |last1=Dhiman |first1=Deeksha |last2=Vatsa |first2=Rakhee |last3=Sood |first3=Ashwani |title=Challenges and opportunities in developing Actinium-225 radiopharmaceuticals |journal=Nuclear Medicine Communications |date=September 2022 |volume=43 |issue=9 |pages=970–977 |doi=10.1097/MNM.0000000000001594|pmid=35950353 }}</ref>

===Actinium-226===
Actinium-226 is an isotope of actinium with a half-life of 29.37 hours. It mainly (83%) undergos [[beta decay]], sometimes (17%) undergo [[electron capture]], and rarely (0.006%) undergo [[alpha decay]].{{NUBASE2020|ref}} There are researches on <sup>226</sup>Ac to use it in [[SPECT]].<ref>{{cite journal | last=Koniar | first=Helena | last2=Rodríguez-Rodríguez | first2=Cristina | last3=Radchenko | first3=Valery | last4=Yang | first4=Hua | last5=Kunz | first5=Peter | last6=Rahmim | first6=Arman | last7=Uribe | first7=Carlos | last8=Schaffer | first8=Paul | title=SPECT imaging of <sup>226</sup>Ac as a theranostic isotope for <sup>225</sup>Ac radiopharmaceutical development | journal=Physics in Medicine and Biology | volume=67 | issue=18 | date=2022-09-12 | issn=1361-6560 | pmid=35985341 | doi=10.1088/1361-6560/ac8b5f}}</ref><ref>{{cite journal | last=Koniar | first=Helena | last2=Wharton | first2=Luke | last3=Ingham | first3=Aidan | last4=Rodríguez-Rodríguez | first4=Cristina | last5=Kunz | first5=Peter | last6=Radchenko | first6=Valery | last7=Yang | first7=Hua | last8=Rahmim | first8=Arman | last9=Uribe | first9=Carlos | last10=Schaffer | first10=Paul | title=In vivoquantitative SPECT imaging of actinium-226: feasibility and proof-of-concept | journal=Physics in Medicine and Biology | volume=69 | issue=15 | date=2024-07-16 | issn=1361-6560 | pmid=38925140 | doi=10.1088/1361-6560/ad5c37| doi-access=free }}</ref>

===Actinium-227===
Actinium-227 is the most stable isotope of actinium, with a half-life of 21.772 years. It mainly (98.62%) undergos [[beta decay]], but sometimes (1.38%) it will undergo [[alpha decay]] instead.{{NUBASE2020|ref}} <sup>227</sup>Ac is a member of the [[actinium series]]. It is found only in traces in [[uranium]] ores&nbsp;– one tonne of uranium in ore contains about 0.2 milligrams of <sup>227</sup>Ac.<ref name="Hagemann1950">{{cite journal |doi=10.1021/ja01158a033 |last1=Hagemann |date=1950 |first1=French |pages=768–771 |volume=72 |journal=Journal of the American Chemical Society |title=The Isolation of Actinium |issue=2}}</ref><ref name="g946">{{Greenwood&Earnshaw2nd|page=946}}</ref> <sup>227</sup>Ac is prepared, in milligram amounts, by the neutron irradiation of {{chem2|^{226}Ra|link=Radium-226}} in a [[nuclear reactor]].<ref name="g946" /><ref>{{cite book |author=Emeleus, H. J. |title=Advances in inorganic chemistry and radiochemistry |url=https://books.google.com/books?id=K5_LSQqeZ_IC&pg=PA16 |date= 1987 |publisher=Academic Press |isbn=978-0-12-023631-2 |pages=16–}}</ref>
:<chem>^{226}_{88}Ra + ^{1}_{0}n -> ^{227}_{88}Ra ->[\beta^-][42.2 \ \ce{min}] ^{227}_{89}Ac</chem>

<sup>227</sup>Ac is highly radioactive and was therefore studied for use as an active element of [[radioisotope thermoelectric generator]]s, for example in spacecraft. The oxide of <sup>227</sup>Ac pressed with [[beryllium]] is also an efficient [[neutron source]] with the activity exceeding that of the standard americium-beryllium and radium-beryllium pairs.<ref name="b1">Russell, Alan M. and Lee, Kok Loong (2005) [https://books.google.com/books?id=fIu58uZTE-gC&pg=PA470 ''Structure-property relations in nonferrous metals'']. Wiley. {{ISBN|0-471-64952-X}}, pp. 470–471</ref> In all those applications, <sup>227</sup>Ac (a beta source) is merely a progenitor which generates alpha-emitting isotopes upon its decay. Beryllium captures alpha particles and emits neutrons owing to its large cross-section for the (α,n) nuclear reaction:

: <chem>^{9}_{4}Be + ^{4}_{2}He -> ^{12}_{6}C + ^{1}_{0}n + \gamma</chem>

The <sup>227</sup>AcBe neutron sources can be applied in a [[neutron probe]]&nbsp;– a standard device for measuring the quantity of water present in soil, as well as moisture/density for quality control in highway construction.<ref>Majumdar, D. K. (2004) [https://books.google.com/books?id=hf1j9v4v3OEC&pg=PA108 ''Irrigation Water Management: Principles and Practice'']. {{ISBN|81-203-1729-7}} p. 108</ref><ref>Chandrasekharan, H. and Gupta, Navindu (2006) [https://books.google.com/books?id=45IDh4Lt8xsC&pg=PA203 ''Fundamentals of Nuclear Science – Application in Agriculture'']. {{ISBN|81-7211-200-9}} pp. 202 ff</ref> Such probes are also used in well logging applications, in [[neutron radiography]], tomography and other radiochemical investigations.<ref>{{cite journal |title = Neutron Spectrum of an Actinium–Beryllium Source |first1 = W. R. |last1 = Dixon |journal = Can. J. Phys. |volume = 35 |issue = 6 |pages = 699–702 |date = 1957 |doi = 10.1139/p57-075 |last2 = Bielesch |first2 = Alice |last3 = Geiger |first3 = K. W.|bibcode = 1957CaJPh..35..699D }}</ref>

The medium half-life of <sup>227</sup>Ac makes it a very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. The associated processes cannot be studied with the required accuracy by direct measurements of current velocities (of the order 50 meters per year). However, evaluation of the concentration depth-profiles for different isotopes allows estimating the mixing rates. The physics behind this method is as follows: oceanic waters contain homogeneously dispersed <sup>235</sup>U. Its decay product, <sup>231</sup>Pa, gradually precipitates to the bottom, so that its concentration first increases with depth and then stays nearly constant. <sup>231</sup>Pa decays to <sup>227</sup>Ac; however, the concentration of the latter isotope does not follow the <sup>231</sup>Pa depth profile, but instead increases toward the sea bottom. This occurs because of the mixing processes which raise some additional <sup>227</sup>Ac from the sea bottom. Thus analysis of both <sup>231</sup>Pa and <sup>227</sup>Ac depth profiles allows researchers to model the mixing behavior.<ref>{{cite journal |last1=Nozaki |first1=Yoshiyuki |title=Excess <sup>227</sup>Ac in deep ocean water |journal=Nature |volume=310 |pages=486–488 |date=1984 |doi=10.1038/310486a0 | issue=5977 | bibcode = 1984Natur.310..486N|s2cid=4344946 }}</ref><ref>{{cite journal |last1=Geibert |first1=W. |last2=Rutgers Van Der Loeff |first2=M. M. |last3=Hanfland |first3=C. |last4=Dauelsberg |first4=H.-J. |title=Actinium-227 as a deep-sea tracer: sources, distribution and applications |journal=Earth and Planetary Science Letters |volume=198 |issue=1–2 |pages=147–165 |date=2002 |doi=10.1016/S0012-821X(02)00512-5 |bibcode=2002E&PSL.198..147G|url=https://doi.pangaea.de/10.1594/PANGAEA.90616 }}</ref>

== See also ==
* [[Decay chain#Actinium series|Actinium series]]
* [[Actinide]]

== Notes ==
{{Reflist | group = note}}
{{Clear}}

== References ==
{{Reflist}}
* Isotope masses from:
**{{NUBASE 2003}}
* Half-life, spin, and isomer data selected from the following sources.
**{{NUBASE 2003}}
**{{NNDC}}
**{{CRC85|chapter=11}}

{{Navbox element isotopes}}
{{Authority control}}

[[Category:Isotopes of actinium| ]]
[[Category:Actinium]]
[[Category:Lists of isotopes by element|Actinium]]