Editing Actinide (section)

== Isotopes ==
{| class="wikitable collapsible collapsed" style="text-align:center;"
!+ colspan=7 | Nuclear properties of isotopes of the most important transplutonium isotopes{{NUBASE2020|ref}}<ref name="tablitsa MAGATE" /><ref>Myasoedov, pp. 19–21</ref>
|-
! rowspan="2"| Isotope
! rowspan="2"| [[Half-life]]
! rowspan="2"| Probability of <br />[[spontaneous fission|spontaneous<br />fission]] in %
! colspan="2"| Emission energy<br />(MeV) (yield in %)
! colspan="2"| Specific activity (Bq/kg)<ref group=notes>Specific activity is calculated by given in the table half-lives and the probability of spontaneous fission</ref> of
|-
! α
! γ
! α, β-particles
! fission
|-
|[[Americium-241|<sup>241</sup>Am]] || 432.2(7) y || 4.3(18){{e|−10}} || 5.485 (84.8) <br />5.442 (13.1)<br />5.388 (1.66) || 0.059 (35.9)<br />0.026 (2.27) || 1.27{{e|14}} || 546.1
|-
|[[Americium-243|<sup>243</sup>Am]] || 7.37(4){{e|3}} y || 3.7(2){{e|−9}} || 5.275 (87.1)<br />5.233 (11.2)<br />5.181 (1.36) || 0.074 (67.2)<br /> 0.043 (5.9) || 7.39{{e|12}} || 273.3
|-
|[[Curium-242|<sup>242</sup>Cm]] || 162.8(2) d || 6.2(3){{e|−6}} || 6.069 (25.92)<br />6.112 (74.08) || 0.044 (0.04)<br />0.102 (4{{e|−3}}) || 1.23{{e|17}} || 7.6{{e|9}}
|-
|[[Curium-244|<sup>244</sup>Cm]] || 18.10(2) y || 1.37(3){{e|−4}} || 5.762 (23.6)<br />5.804 (76.4) || 0.043 (0.02)<br />0.100 (1.5{{e|−3}}) || 2.96{{e|15}} || 4.1{{e|9}}
|-
|[[Curium-245|<sup>245</sup>Cm]] || 8.5(1){{e|3}} y || 6.1(9){{e|−7}} || 5.529 (0.58)<br />5.488 (0.83)<br />5.361 (93.2) || 0.175 (9.88)<br />0.133 (2.83) || 6.35{{e|12}} || 3.9{{e|4}}
|-
|[[Curium-246|<sup>246</sup>Cm]] || 4.76(4){{e|3}} y || 0.02615(7) || 5.343 (17.8)<br />5.386 (82.2) || 0.045 (19) || 1.13{{e|13}} || 2.95{{e|9}}
|-
|[[Curium-247|<sup>247</sup>Cm]] || 1.56(5){{e|7}} y || — || 5.267 (13.8)<br />5.212 (5.7)<br />5.147 (1.2) || 0.402 (72)<br />0.278 (3.4) || 3.43{{e|9}} ||—
|-
|[[Curium-248|<sup>248</sup>Cm]] || 3.48(6){{e|5}} y || 8.39(16) || 5.034 (16.52)<br />5.078 (75) ||—|| 1.40{{e|11}} || 1.29{{e|10}}
|-
|[[Berkelium-249|<sup>249</sup>Bk]] || 330(4) d || 4.7(2){{e|−8}} || 5.406 (1{{e|−3}})<br />5.378 (2.6{{e|−4}}) || 0.32 (5.8{{e|−5}}) || 5.88{{e|16}} || 2.76{{e|7}}
|-
|[[Californium-249|<sup>249</sup>Cf]] || 351(2) y || 5.0(4){{e|−7}} || 6.193 (2.46)<br />6.139 (1.33)<br />5.946 (3.33) || 0.388 (66)<br />0.333 (14.6) || 1.51{{e|14}} || 7.57{{e|5}}
|-
|[[Californium-250|<sup>250</sup>Cf]] || 13.08(9) y || 0.077(3) || 5.988 (14.99)<br />6.030 (84.6) || 0.043 || 4.04{{e|15}} || 3.11{{e|12}}
|-
|[[Californium-251|<sup>251</sup>Cf]] || 900(40) y || ? || 6.078 (2.6)<br />5.567 (0.9)<br />5.569 (0.9) || 0.177 (17.3)<br />0.227 (6.8) || 5.86{{e|13}} ||—
|-
|[[Californium-252|<sup>252</sup>Cf]] || 2.645(8) y || 3.092(8) || 6.075 (15.2)<br />6.118 (81.6) || 0.042 (1.4{{e|−2}})<br />0.100 (1.3{{e|−2}}) || 1.92{{e|16}} || 6.14{{e|14}}
|-
|[[Californium-254|<sup>254</sup>Cf]] || 60.5(2) d || ≈100 || 5.834 (0.26)<br />5.792 (5.3{{e|−2}}) ||—|| 9.75{{e|14}} || 3.13{{e|17}}
|-
|[[Einsteinium-253|<sup>253</sup>Es]] || 20.47(3) d || 8.7(3){{e|−6}} || 6.540 (0.85)<br />6.552 (0.71)<br />6.590 (6.6) || 0.387 (0.05)<br />0.429 (8{{e|−3}}) || 9.33{{e|17}} || 8.12{{e|10}}
|-
|[[Einsteinium-254|<sup>254</sup>Es]] || 275.7(5) d || < 3{{e|−6}} || 6.347 (0.75)<br />6.358 (2.6)<br />6.415 (1.8) || 0.042 (100)<br />0.034 (30) || 6.9{{e|16}} ||—
|-
|[[Einsteinium-255|<sup>255</sup>Es]] || 39.8(12) d || 0.0041(2) || 6.267 (0.78)<br />6.401 (7) ||—|| 4.38{{e|17}}(β)<br />3.81{{e|16}}(α) || 1.95{{e|13}}
|-
|[[Fermium-255|<sup>255</sup>Fm]] || 20.07(7) h || 2.4(10){{e|−5}} || 7.022 (93.4)<br />6.963 (5.04)<br />6.892 (0.62) || 0.00057 (19.1)<br />0.081 (1) || 2.27{{e|19}} || 5.44{{e|12}}
|-
|[[Fermium-256|<sup>256</sup>Fm]] || 157.6(13) min || 91.9(3) || 6.872 (1.2)<br />6.917 (6.9) ||—||1.58{{e|20}} || 1.4{{e|19}}
|-
|[[Fermium-257|<sup>257</sup>Fm]] || 100.5(2) d || 0.210(4) || 6.752 (0.58)<br />6.695 (3.39)<br />6.622 (0.6) || 0.241 (11)<br />0.179 (8.7) || 1.87{{e|17}} || 3.93{{e|14}}
|-
|[[Mendelevium-256|<sup>256</sup>Md]] || 77(2) min ||—|| 7.142 (1.84)<br />7.206 (5.9) ||—||3.53{{e|20}} ||—
|-
|[[Mendelevium-257|<sup>257</sup>Md]] || 5.52(5) h ||—|| 7.074 (14) || 0.371 (11.7)<br />0.325 (2.5) ||8.17{{e|19}}||—
|-
|[[Mendelevium-258|<sup>258</sup>Md]] || 51.5(3) d ||—|| 6.73||—||3.64{{e|17}} ||—
|-
|[[Nobelium-255|<sup>255</sup>No]] || 3.1(2) min ||—|| 8.312 (1.16)<br />8.266 (2.6)<br />8.121 (27.8) || 0.187 (3.4) || 8.78{{e|21}} ||—
|-
|[[Nobelium-259|<sup>259</sup>No]] || 58(5) min ||—|| 7.455 (9.8)<br />7.500 (29.3)<br />7.533 (17.3) ||—||4.63{{e|20}}||—
|-
|[[Lawrencium-256|<sup>256</sup>Lr]] || 27(3) s ||< 0.03|| 8.319 (5.4)<br />8.390 (16)<br />8.430 (33) ||—|| 5.96{{e|22}} ||—
|-
|[[Lawrencium-257|<sup>257</sup>Lr]] || 646(25) ms ||—|| 8.796 (18)<br />8.861 (82) ||—||1.54{{e|24}}||—
|}

[[File:Isotopes and half-life.svg|thumb|upright=1.5|Actinides have 89–103 protons and usually 117–159 neutrons.]]
Thirty-four [[isotopes of actinium]] and eight excited [[nuclear isomerism|isomeric states]] of some of its [[nuclide]]s are known, ranging in mass number from 203 to 236.{{NUBASE2020|ref}} Three isotopes, [[Actinium-225|<sup>225</sup>Ac]], [[Actinium-227|<sup>227</sup>Ac]] and [[Actinium-228|<sup>228</sup>Ac]], were found in nature and the others were produced in the laboratory; only the three natural isotopes are used in applications. Actinium-225 is a member of the radioactive [[neptunium series]];<ref name=g1254>Greenwood, p. 1254</ref> it was first discovered in 1947 as a decay product of [[uranium-233]] and it is an α-emitter with a half-life of 10 days. Actinium-225 is less available than actinium-228, but is more promising in radiotracer applications.<ref name="Himiya aktiniya" /> Actinium-227 (half-life 21.77 years) occurs in all uranium ores, but in small quantities. One gram of uranium (in radioactive equilibrium) contains only 2{{e|-10}} gram of <sup>227</sup>Ac.<ref name="Himiya aktiniya" />{{NUBASE2020|ref}} Actinium-228 is a member of the [[Radioactive series#Thorium series|radioactive thorium series]] formed by the decay of [[Radium-228|<sup>228</sup>Ra]];<ref name=g1254 /> it is a β<sup>−</sup> emitter with a half-life of 6.15 hours. In one tonne of thorium there is 5{{e|-8}} gram of <sup>228</sup>Ac. It was discovered by [[Otto Hahn]] in 1906.<ref name="Himiya aktiniya" />

There are 32 known [[isotopes of thorium]] ranging in mass number from 207 to 238.{{NUBASE2020|ref}} Of these, the longest-lived is <sup>232</sup>Th, whose half-life of {{val|1.4|e=10|u=years}} means that it still exists in nature as a [[primordial nuclide]]. The next longest-lived is <sup>230</sup>Th, an intermediate decay product of <sup>238</sup>U with a half-life of 75,400 years. Several other thorium isotopes have half-lives over a day; all of these are also transient in the decay chains of <sup>232</sup>Th, <sup>235</sup>U, and <sup>238</sup>U.

Twenty-nine [[isotopes of protactinium]] are known with mass numbers 211–239{{NUBASE2020|ref}} as well as three excited [[nuclear isomerism|isomeric states]]. Only [[protactinium-231|<sup>231</sup>Pa]] and [[protactinium-234|<sup>234</sup>Pa]] have been found in nature. All the isotopes have short lifetimes, except for protactinium-231 (half-life 32,760 years). The most important isotopes are <sup>231</sup>Pa and [[protactinium-233|<sup>233</sup>Pa]], which is an intermediate product in obtaining uranium-233 and is the most affordable among artificial isotopes of protactinium. <sup>233</sup>Pa has convenient half-life and energy of [[Gamma radiation|γ-radiation]], and thus was used in most studies of protactinium chemistry. Protactinium-233 is a [[Beta radiation|β-emitter]] with a half-life of 26.97 days.{{NUBASE2020|ref}}<ref name="Himiya protaktiniya" />

There are 27 known [[isotopes of uranium]], having mass numbers 215–242 (except 220).<ref name="tablitsa MAGATE" /> Three of them, [[Uranium-234|<sup>234</sup>U]], <sup>235</sup>U and <sup>238</sup>U, are present in appreciable quantities in nature. Among others, the most important is <sup>233</sup>U, which is a final product of transformation of [[Thorium-232|<sup>232</sup>Th]] irradiated by slow neutrons. <sup>233</sup>U has a much higher fission efficiency by low-energy (thermal) neutrons, compared e.g. with <sup>235</sup>U. Most uranium chemistry studies were carried out on uranium-238 owing to its long half-life of 4.4{{e|9}} years.<ref>{{cite book|author=I.P. Alimarin|title=Analytical chemistry of uranium|editor=A.P. Vinogradov|location=Moscow|publisher=Publisher USSR Academy of Sciences|year=1962}}</ref>

There are 25 [[isotopes of neptunium]] with mass numbers 219–244 (except 221);<ref name="tablitsa MAGATE" /> they are all highly radioactive. The most popular among scientists are long-lived <sup>237</sup>Np (t<sub>1/2</sub>&nbsp;= 2.20{{e|6}} years) and short-lived <sup>239</sup>Np, <sup>238</sup>Np (t<sub>1/2</sub>&nbsp;~ 2 days).<ref name="Himiya neptuniya" />

There are 21 known [[isotopes of plutonium]], having mass numbers 227–247.<ref name="tablitsa MAGATE" /> The most stable isotope of plutonium is <sup>244</sup>Pu with half-life of 8.13{{e|7}} years.{{NUBASE2020|ref}}

Eighteen [[isotopes of americium]] are known with mass numbers from 229 to 247 (with the exception of 231).<ref name="tablitsa MAGATE" /> The most important are <sup>241</sup>Am and <sup>243</sup>Am, which are alpha-emitters and also emit soft, but intense γ-rays; both of them can be obtained in an isotopically pure form. Chemical properties of americium were first studied with <sup>241</sup>Am, but later shifted to <sup>243</sup>Am, which is almost 20 times less radioactive. The disadvantage of <sup>243</sup>Am is production of the short-lived daughter isotope <sup>239</sup>Np, which has to be considered in the data analysis.<ref name=m18>Myasoedov, p. 18</ref>

Among 19 [[isotopes of curium]], ranging in mass number from 233 to 251,<ref name="tablitsa MAGATE" /> the most accessible are <sup>242</sup>Cm and <sup>244</sup>Cm; they are α-emitters, but with much shorter lifetime than the americium isotopes. These isotopes emit almost no γ-radiation, but undergo [[spontaneous fission]] with the associated emission of neutrons. More long-lived isotopes of curium (<sup>245–248</sup>Cm, all α-emitters) are formed as a mixture during neutron irradiation of plutonium or americium. Upon short irradiation, this mixture is dominated by <sup>246</sup>Cm, and then <sup>248</sup>Cm begins to accumulate. Both of these isotopes, especially <sup>248</sup>Cm, have a longer half-life (3.48{{e|5}} years) and are much more convenient for carrying out chemical research than <sup>242</sup>Cm and <sup>244</sup>Cm, but they also have a rather high rate of spontaneous fission. <sup>247</sup>Cm has the longest lifetime among isotopes of curium (1.56{{e|7}} years), but is not formed in large quantities because of the strong fission induced by thermal neutrons.

Seventeen [[isotopes of berkelium]] have been identified with mass numbers 233, 234, 236, 238, and 240–252.<ref name="tablitsa MAGATE" /> Only <sup>249</sup>Bk is available in large quantities; it has a relatively short half-life of 330 days and emits mostly soft [[Beta decay|β-particles]], which are inconvenient for detection. Its [[alpha radiation]] is rather weak (1.45{{e|-3}}% with respect to β-radiation), but is sometimes used to detect this isotope. <sup>247</sup>Bk is an alpha-emitter with a long half-life of 1,380 years, but it is hard to obtain in appreciable quantities; it is not formed upon neutron irradiation of plutonium because β-decay of curium isotopes with mass number below 248 is not known.<ref name=m18 /> (<sup>247</sup>Cm would actually release energy by β-decaying to <sup>247</sup>Bk, but this has never been seen.)

The 20 [[isotopes of californium]] with mass numbers 237–256 are formed in nuclear reactors;<ref name="tablitsa MAGATE" /> californium-253 is a β-emitter and the rest are α-emitters. The isotopes with even mass numbers (<sup>250</sup>Cf, <sup>252</sup>Cf and <sup>254</sup>Cf) have a high rate of spontaneous fission, especially <sup>254</sup>Cf of which 99.7% decays by spontaneous fission. Californium-249 has a relatively long half-life (352 years), weak spontaneous fission and strong γ-emission that facilitates its identification. <sup>249</sup>Cf is not formed in large quantities in a nuclear reactor because of the slow β-decay of the parent isotope <sup>249</sup>Bk and a large cross section of interaction with neutrons, but it can be accumulated in the isotopically pure form as the β-decay product of (pre-selected) <sup>249</sup>Bk. Californium produced by reactor-irradiation of plutonium mostly consists of <sup>250</sup>Cf and <sup>252</sup>Cf, the latter being predominant for large neutron fluences, and its study is hindered by the strong neutron radiation.<ref name=m22>Myasoedov, p. 22</ref>

{| class="wikitable"  style="float:right; text-align:center;"
|+ Properties of some transplutonium isotope pairs<ref>Myasoedov, p. 25</ref>
! Parent <br />isotope
! t<sub>1/2</sub>
! Daughter <br />isotope
! t<sub>1/2</sub>
! Time to establish <br />radioactive equilibrium
|-
| <sup>243</sup>Am|| 7370 years|| <sup>239</sup>Np|| 2.35 days|| 47.3 days
|-
| <sup>245</sup>Cm|| 8265 years|| <sup>241</sup>Pu|| 14 years|| 129 years
|-
| <sup>247</sup>Cm|| 1.64{{e|7}} years|| <sup>243</sup>Pu|| 4.95 hours|| 7.2 days
|-
| <sup>254</sup>Es|| 270 days|| <sup>250</sup>Bk|| 3.2 hours|| 35.2 hours
|-
| <sup>255</sup>Es|| 39.8 days|| <sup>255</sup>Fm|| 22 hours|| 5 days
|-
| <sup>257</sup>Fm|| 79 days|| <sup>253</sup>Cf|| 17.6 days|| 49 days
|}

Among the 18 known [[isotopes of einsteinium]] with mass numbers from 240 to 257,<ref name="tablitsa MAGATE">{{cite web|url=http://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html|title=Table of nuclides, IAEA|access-date=7 July 2010}}</ref> the most affordable is <sup>253</sup>Es. It is an α-emitter with a half-life of 20.47 days, a relatively weak γ-emission and small spontaneous fission rate as compared with the isotopes of californium. Prolonged neutron irradiation also produces a long-lived isotope <sup>254</sup>Es (t<sub>1/2</sub>&nbsp;= 275.5 days).<ref name=m22 />

Twenty [[isotopes of fermium]] are known with mass numbers of 241–260. <sup>254</sup>Fm, <sup>255</sup>Fm and <sup>256</sup>Fm are [[Alpha radiation|α-emitters]] with a short half-life (hours), which can be isolated in significant amounts. <sup>257</sup>Fm (t<sub>1/2</sub> = 100 days) can accumulate upon prolonged and strong irradiation. All these isotopes are characterized by high rates of spontaneous fission.<ref name=m22 /><ref name="Tablitsa izotopov">{{cite web|url=http://elm.e-science.ru/|title=Table of elements, compounds, isotopes|language=ru|access-date=7 July 2010|archive-url=https://web.archive.org/web/20100712111619/http://elm.e-science.ru/|archive-date=12 July 2010|url-status=dead}}</ref>

Among the 17 known [[isotopes of mendelevium]] (mass numbers from 244 to 260),<ref name="tablitsa MAGATE" /> the most studied is <sup>256</sup>Md, which mainly decays through electron capture (α-radiation is ≈10%) with a half-life of 77 minutes. Another alpha emitter, <sup>258</sup>Md, has a half-life of 53 days. Both these isotopes are produced from rare einsteinium (<sup>253</sup>Es and <sup>255</sup>Es respectively), that therefore limits their availability.{{NUBASE2020|ref}}

Long-lived [[isotopes of nobelium]] and [[isotopes of lawrencium]] (and of heavier elements) have relatively short half-lives. For nobelium, 13 isotopes are known, with mass numbers 249–260 and 262. The chemical properties of nobelium and lawrencium were studied with <sup>255</sup>No (t<sub>1/2</sub>&nbsp;= 3&nbsp;min) and <sup>256</sup>Lr (t<sub>1/2</sub>&nbsp;= 35&nbsp;s). The longest-lived nobelium isotope, <sup>259</sup>No, has a half-life of approximately 1 hour.{{NUBASE2020|ref}} Lawrencium has 14 known isotopes with mass numbers 251–262, 264, and 266. The most stable of them is <sup>266</sup>Lr with a half life of 11 hours.

Among all of these, the only isotopes that occur in sufficient quantities in nature to be detected in anything more than traces and have a measurable contribution to the atomic weights of the actinides are the primordial <sup>232</sup>Th, <sup>235</sup>U, and <sup>238</sup>U, and three long-lived decay products of natural uranium, <sup>230</sup>Th, <sup>231</sup>Pa, and <sup>234</sup>U. Natural thorium consists of 0.02(2)% <sup>230</sup>Th and 99.98(2)% <sup>232</sup>Th; natural protactinium consists of 100% <sup>231</sup>Pa; and natural uranium consists of 0.0054(5)% <sup>234</sup>U, 0.7204(6)% <sup>235</sup>U, and 99.2742(10)% <sup>238</sup>U.<ref>[http://www.ciaaw.org/atomic-weights.htm Standard Atomic Weights 2013]. [[Commission on Isotopic Abundances and Atomic Weights]]</ref>