View source for Isotopes of americium

{{Short description|none}}
{{Infobox americium isotopes}}
[[Americium]] (<sub>95</sub>Am) is an [[artificial element]], and thus a [[standard atomic weight]] cannot be given. Like all artificial elements, it has no known [[stable isotopes]]. The first [[isotope]] to be synthesized was <sup>241</sup>Am in 1944.  The artificial element decays by ejecting [[alpha particles]].  Americium has an atomic number of 95 (the number of protons in the nucleus of the americium atom). Despite {{chem|243|Am}} being an order of magnitude longer lived than {{chem|241|Am}}, the former is harder to obtain than the latter as more of it is present in [[spent nuclear fuel]].

Eighteen [[radioisotope]]s of americium, ranging from <sup>229</sup>Am to <sup>247</sup>Am with the exception of <sup>231</sup>Am, have been characterized; another isotope, <sup>223</sup>Am, has also been reported but is unconfirmed. The most stable isotopes are <sup>243</sup>Am with a [[half-life]] of 7,370 years and <sup>241</sup>Am with a half-life of 432.2 years. All of the remaining [[radioactive decay|radioactive]] isotopes have half-lives that are less than seven days, the majority of which are shorter than two hours. This element also has fourteen [[meta state]]s, with the most stable being <sup>242m1</sup>Am (half-life 141 years). This isomer is unusual in that its half-life is far longer than that of the ground state of the same isotope.

== List of isotopes ==
{{Anchor|Americium-224|Americium-225|Americium-226|Americium-227|Americium-228|Americium-231|Americium-248|Americium-249}}
<!--Please delete anchor(s) from the list above or table below if adding a dedicated isotope section(s).-->
{{Isotopes table
| symbol = Am
| refs = NUBASE2020, AME2020 II
| notes = m, unc(), mass#, exen#, spin(), spin#, CD, EC, IT, SF
}}
|-id=Americium-223
| <sup>223</sup>Am{{refn|group=n|The discovery of this isotope is uncertain due to disagreements between theoretical predictions and reported experimental data.<ref name=Np223>{{cite journal |title=New short-lived isotope <sup>223</sup>Np and the absence of the Z = 92 subshell closure near N = 126
|first=M. D. |last=Sun |display-authors=et al. |journal=Physics Letters B |volume=771 |date=2017 |pages=303–308 |doi=10.1016/j.physletb.2017.03.074 |url=https://www.researchgate.net/publication/317142406|doi-access=free |bibcode=2017PhLB..771..303S }}</ref>}}
| style="text-align:right" | 95
| style="text-align:right" | 128
| 223.04584(32)#
| {{val|10|(9)|u=ms}}
| [[alpha decay|α]]
| <sup>219</sup>Np
| 9/2–#
|-id=Americium-229
| <sup>229</sup>Am
| style="text-align:right" | 95
| style="text-align:right" | 134
| 229.04528(11)
| {{val|1.8|(15)|u=s}}
| α
| <sup>225</sup>Np
| 5/2–#
|-id=Americium-230
| rowspan=2 | <sup>230</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 135
| rowspan=2 | 230.04603(15)#
| rowspan=2 | {{val|40|(9)|u=s}}
| [[beta decay|β<sup>+</sup>]] (<70%)
| <sup>230</sup>Pu
| rowspan=2 | 1–#
|-
| β<sup>+</sup>, [[Spontaneous fission|SF]] (>30%)
| (various)
|-id=Americium-232
| rowspan=3 | <sup>232</sup>Am
| rowspan=3 style="text-align:right" | 95
| rowspan=3 style="text-align:right" | 137
| rowspan=3 | 232.04661(32)#
| rowspan=3 | {{val|1.31|(4)|u=min}}
| β<sup>+</sup> (97%)
| <sup>232</sup>Pu
| rowspan=3 | 1–#
|-
| α? (3%)
| <sup>228</sup>Np
|-
| β<sup>+</sup>, SF (0.069%)
| (various)
|-id=Americium-233
| rowspan=2 | <sup>233</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 138
| rowspan=2 | 233.04647(12)#
| rowspan=2 | {{val|3.2|(8)|u=min}}
| β<sup>+</sup>? (95.5%)
| <sup>233</sup>Pu
| rowspan=2 | 5/2–#
|-
| α (4.5%)
| <sup>229</sup>Np
|-id=Americium-234
| rowspan=3 | <sup>234</sup>Am
| rowspan=3 style="text-align:right" | 95
| rowspan=3 style="text-align:right" | 139
| rowspan=3 | 234.04773(17)#
| rowspan=3 | {{val|2.32|(8)|u=min}}
| β<sup>+</sup> (99.95%)
| <sup>234</sup>Pu
| rowspan=3 | 0–#
|-
| α (0.039%)
| <sup>230</sup>Np
|-
| β<sup>+</sup>, SF (0.0066%)
| (various)
|-id=Americium-235
| rowspan=2 | <sup>235</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 140
| rowspan=2 | 235.04791(6)
| rowspan=2 | {{val|10.3|(6)|u=min}}
| β<sup>+</sup> (99.60%)
| <sup>235</sup>Pu
| rowspan=2 | 5/2−#
|-
| α (0.40%)
| <sup>231</sup>Np
|-id=Americium-236
| rowspan=2 | <sup>236</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 141
| rowspan=2 | 236.04943(13)#
| rowspan=2 | {{val|3.6|(1)|u=min}}
| β<sup>+</sup>
| <sup>236</sup>Pu
| rowspan=2 | 5−
|-
| α (4×10<sup>−3</sup>%)
| <sup>232</sup>Np
|-id=Americium-236m
| style="text-indent:1em" | <sup>236m</sup>Am
| colspan=3 style="text-indent:2em" | 50(50)#&nbsp;keV
| {{val|2.9|(2)|u=min}}
| β<sup>+</sup>
| <sup>236</sup>Pu
| (1−)
|-id=Americium-237
| rowspan=2 | <sup>237</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 142
| rowspan=2 | 237.05000(6)#
| rowspan=2 | {{val|73.6|(8)|u=min}}
| β<sup>+</sup> (99.975%)
| <sup>237</sup>Pu
| rowspan=2 | 5/2−
|-
| α (0.025%)
| <sup>233</sup>Np
|-id=Americium-238
| rowspan=2 | <sup>238</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 143
| rowspan=2 | 238.05198(6)
| rowspan=2 | {{val|98|(3)|u=min}}
| β<sup>+</sup>
| <sup>238</sup>Pu
| rowspan=2 | 1+
|-
| α (1.0×10<sup>−4</sup>%)
| <sup>234</sup>Np
|-id=Americium-238m
| style="text-indent:1em" | <sup>238m</sup>Am
| colspan="3" style="text-indent:2em" | 2500(200)#&nbsp;keV 
| {{val|35|(18)|u=us}}
| SF
| (various)
| 
|-id=Americium-239
| rowspan=2 | <sup>239</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 144
| rowspan=2 | 239.0530227(21)
| rowspan=2 | {{val|11.9|(1)|u=h}}
| [[Electron capture|EC]] (99.990%)
| <sup>239</sup>Pu
| rowspan=2 | 5/2−
|-
| α (0.010%)
| <sup>235</sup>Np
|-id=Americium-239m
| style="text-indent:1em" | <sup>239m</sup>Am
| colspan="3" style="text-indent:2em" | 2500(200)&nbsp;keV
| {{val|163|(12)|u=ns}}
| SF
| (various)
| (7/2+)
|-id=Americium-240
| rowspan=2 | <sup>240</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 145
| rowspan=2 | 240.055298(15)
| rowspan=2 | {{val|50.8|(3)|u=h}}
| β<sup>+</sup>
| <sup>240</sup>Pu
| rowspan=2 | (3−)
|-
| α (1.9×10<sup>−4</sup>%)
| <sup>236</sup>Np
|-id=Americium-240m
| style="text-indent:1em" | <sup>240m</sup>Am
| colspan="3" style="text-indent:2em" | 3000(200)&nbsp;keV
| {{val|940|(40)|u=us}}
| SF
| (various)
| 
|-
| rowspan=2 | [[Americium-241|<sup>241</sup>Am]]
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 146
| rowspan=2 | 241.0568273(12)
| rowspan=2 | {{val|432.6|(6)|u=y}}
| α
| <sup>237</sup>Np
| rowspan=2 | 5/2−
|-
| SF (3.6×10<sup>−10</sup>%)
| (various)
|-id=Americium-241m
| style="text-indent:1em" | <sup>241m</sup>Am
| colspan="3" style="text-indent:2em" | 2200(200)&nbsp;keV
| {{val|1.2|(3)|u=us}}
| SF
| (various)
|
|-id=Americium-242
| rowspan=2 | <sup>242</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 147
| rowspan=2 | 242.0595474(12)
| rowspan=2 | {{val|16.02|(2)|u=h}}
| β<sup>−</sup> (82.7%)
| <sup>242</sup>Cm
| rowspan=2 | 1−
|-
| EC (17.3%)
| <sup>242</sup>Pu
|-
| rowspan=3 style="text-indent:1em" | <sup>242m1</sup>Am
| rowspan=3 colspan="3" style="text-indent:2em" | 48.60(5)&nbsp;keV
| rowspan=3 | {{val|141|(2)|u=y}}
| [[Isomeric transition|IT]] (99.55%)
| <sup>242</sup>Am
| rowspan=3 | 5−
|-
| α (0.45%)
| <sup>238</sup>Np
|-
| SF (<4.7×10<sup>−9</sup>%)
| (various)
|-id=Americium-242m2
| rowspan=2 style="text-indent:1em" | <sup>242m2</sup>Am
| rowspan=2 colspan="3" style="text-indent:2em" | 2200(80)&nbsp;keV
| rowspan=2 | {{val|14.0|(10)|u=ms}}
| SF
| (various)
| rowspan=2 | (2+, 3−)
|-
| IT
| <sup>242</sup>Am
|-
| rowspan=2 | <sup>243</sup>Am
| rowspan=2 style="text-align:right" | 95
| rowspan=2 style="text-align:right" | 148
| rowspan=2 | 243.0613799(15)
| rowspan=2 | {{val|7350|(9)|u=y}}
| α
| <sup>239</sup>Np
| rowspan=2 | 5/2−
|-
| SF (3.7×10<sup>−9</sup>%)
| (various)
|-id=Americium-243m
| style="text-indent:1em" | <sup>243m</sup>Am
| colspan="3" style="text-indent:2em" | 2300(200)&nbsp;keV
| {{val|5.5|(5)|u=us}}
| SF
| (various)
| 
|-id=Americium-244
| <sup>244</sup>Am
| style="text-align:right" | 95
| style="text-align:right" | 149
| 244.0642829(16)
| {{val|10.01|(3)|u=h}}
| β<sup>−</sup>
| <sup>244</sup>Cm
| (6−)
|-id=Americium-244m1
| rowspan=2 style="text-indent:1em" | <sup>244m1</sup>Am
| rowspan=2 colspan="3" style="text-indent:2em" | 89.3(16)&nbsp;keV
| rowspan=2 | {{val|26.13|(43)|u=min}}
| β<sup>−</sup> (99.96%)
| <sup>244</sup>Cm
| rowspan=2 | 1+
|-
| EC (0.0364%)
| <sup>244</sup>Pu
|-id=Americium-244m2
| style="text-indent:1em" | <sup>244m2</sup>Am
| colspan="3" style="text-indent:2em" | 2000(200)#&nbsp;keV
| {{val|0.90|(15)|u=ms}}
| SF
| (various)
| 
|-id=Americium-244m3
| style="text-indent:1em" | <sup>244m3</sup>Am
| colspan="3" style="text-indent:2em" | 2200(200)#&nbsp;keV
| ~{{val|6.5|u=us}}
| SF
| (various)
| 
|-id=Americium-245
| <sup>245</sup>Am
| style="text-align:right" | 95
| style="text-align:right" | 150
| 245.0664528(20)
| {{val|2.05|(1)|u=h}}
| β<sup>−</sup>
| <sup>245</sup>Cm
| 5/2+
|-id=Americium-245m
| style="text-indent:1em" | <sup>245m</sup>Am
| colspan="3" style="text-indent:2em" | 2400(400)#&nbsp;keV
| {{val|0.64|(6)|u=us}}
| SF
| (various)
| 
|-id=Americium-246
| <sup>246</sup>Am
| style="text-align:right" | 95
| style="text-align:right" | 151
| 246.069774(19)#
| {{val|39|(3)|u=min}}
| β<sup>−</sup>
| <sup>246</sup>Cm
| 7−
|-id=Americium-246m1
| style="text-indent:1em" | <sup>246m1</sup>Am
| colspan="3" style="text-indent:2em" | 30(10)#&nbsp;keV
| {{val|25.0|(2)|u=min}}
| β<sup>−</sup>
| <sup>246</sup>Cm
| 2(−)
|-id=Americium-246m2
| style="text-indent:1em" | <sup>246m2</sup>Am
| colspan="3" style="text-indent:2em" | 2000(800)#&nbsp;keV
| {{val|73|(10)|u=us}}
| SF
| (various)
| 
|-id=Americium-247
| <sup>247</sup>Am
| style="text-align:right" | 95
| style="text-align:right" | 152
| 247.07209(11)#
| {{val|23.0|(13)|u=min}}
| β<sup>−</sup>
| <sup>247</sup>Cm
| 5/2#
{{Isotopes table/footer}}

== Actinides vs fission products ==
{{Actinidesvsfissionproducts}}
{{clear}}

== Notable isotopes ==

=== Americium-241 ===
[[File:Americium button hd.jpg|thumb|200px|Americium-241 is used in ionization [[smoke detector]]s.]]
{{main|Americium-241}}

'''Americium-241''' is the most common isotope of americium in nuclear waste.<ref name="anl">[http://www.ead.anl.gov/pub/doc/Americium.pdf "Americium"] {{webarchive|url=https://web.archive.org/web/20120730003822/http://www.ead.anl.gov/pub/doc/americium.pdf |date=2012-07-30 }}. Argonne National Laboratory, EVS. Retrieved 25 December 2009.</ref> It is the isotope used in an [[americium smoke detector]] based on an [[ionization chamber]]. It is a potential fuel for long-lifetime [[radioisotope thermoelectric generator]]s.

{| class="wikitable"
|- 
! Parameter !! Value
|-
| [[Atomic mass]]
| align=right | {{val|241.0568273|ul=Da}}
|-
| [[Mass excess]]
| align=right | 52930 [[electronvolt|keV]]
|-
| [[Beta decay]] [[decay energy|energy]]
| align=right | −767&nbsp;keV
|-
| [[Spin (physics)|Spin]]
| align=right | 5/2−
|-
| [[Half-life]]
| align=right | 432.6 years
|-
| [[Spontaneous fission]]s
| align=right | 1200 per kg s
|-
| [[Decay heat]]
| align=right | 114 watts/kg
|-
|}

Possible parent nuclides: beta from [[Plutonium-241|{{sup|241}}Pu]], electron capture from {{sup|241}}Cm, alpha from {{sup|245}}Bk.

{{sup|241}}Am [[alpha decay]]s, with a by-product of [[gamma ray]]s. Its presence in [[plutonium]] is determined by the original concentration of {{sup|241}}Pu and the sample age. Due to the low penetration of alpha radiation, {{sup|241}}Am only poses a health risk when ingested or inhaled. Older samples of plutonium containing plutonium-241 contain a buildup of {{sup|241}}Am. A chemical removal of americium from reworked plutonium (e.g. during reworking of [[plutonium pit]]s) may be required.

=== Americium-242m ===
{{Anchor|Americium-242m1}}
[[File:Sasahara.svg|thumb|375px|Transmutation flow between {{sup|238}}Pu and {{sup|244}}Cm in LWR.<ref name="Am242-Sasahara">{{cite journal|url=https://www.tandfonline.com/doi/pdf/10.1080/18811248.2004.9715507?needAccess=true |title=Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels |journal=Journal of Nuclear Science and Technology |volume=41 |issue=4 |pages=448–456 |date=April 2004 |doi=10.3327/jnst.41.448 |last1=Sasahara |first1=Akihiro |last2=Matsumura |first2=Tetsuo |last3=Nicolaou |first3=Giorgos |last4=Papaioannou |first4=Dimitri |doi-access=free }}</ref>{{br}}Fission percentage is 100 minus shown percentages.{{br}}Total rate of transmutation varies greatly by nuclide.{{br}}{{sup|245}}Cm–{{sup|248}}Cm are long-lived with negligible decay.]]
{| class="wikitable"
|+{{sup|242m}}Am decay modes ([[half-life]]: 141 years){{NUBASE2020|ref}}
!Probability!!Decay mode!![[Decay energy]]!![[Decay product]]
|-
|99.55%||[[isomeric transition]]||0.049 [[MeV]]||{{sup|242}}Am
|-
|&nbsp;&nbsp;0.45%||[[alpha decay]]||5.64 MeV||{{sup|238}}Np
|-
| {{val|1.5|0.6|e=-10}}{{tsp}}<ref name="242Am-Calswell">{{cite journal |journal=Physical Review |volume=155 |issue = 4|date=March 1967 |author=J. T. Caldwell |author2=S. C. Fultz |author3=C. D. Bowman |author4=R. W. Hoff |title=Spontaneous Fission Half-Life of Am{{sup|242''m''}} |doi=10.1103/PhysRev.155.1309 |pages=1309–1313|bibcode=1967PhRv..155.1309C }} (halflife (9.5±3.5)×10{{sup|11}} years)</ref>||[[spontaneous fission]]||~200 MeV||[[fission product]]s
|}

'''Americium-242m''' has a mass of 242.0595492&nbsp;g/mol. It is one of the rare cases, like [[isotopes of silver|{{sup|108m}}Ag]], [[isotopes of holmium|{{sup|166m}}Ho]], [[isotopes of tantalum#Tantalum-180m|{{sup|180m}}Ta]], [[isotopes of rhenium|{{sup|186m}}Re]], [[isotopes of iridium|{{sup|192m}}Ir]], [[isotopes of bismuth|{{sup|210m}}Bi]], [[isotopes of polonium|{{sup|212m}}Po]] and others, where a higher-energy [[nuclear isomer]] is more stable than the ground state, '''americium-242'''.<ref name="242Am-matpack">[http://www.matpack.de/Info/Nuclear/Nuclids/A/Am242.html 95-Am-242] {{webarchive|url=https://web.archive.org/web/20110719060944/http://www.matpack.de/Info/Nuclear/Nuclids/A/Am242.html |date=2011-07-19 }}</ref>

{{sup|242m}}Am is [[fissile]] with a low [[critical mass]], comparable to that of [[plutonium-239|{{sup|239}}Pu]].<ref name="242Am-typhoon">{{cite web |title=Critical Mass Calculations for {{sup|241}}Am, {{sup|242m}}Am and {{sup|243}}Am |url=http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf |archive-url=https://web.archive.org/web/20110722105207/http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf |url-status=dead |archive-date=July 22, 2011 |access-date=February 3, 2011 }}</ref> It has a very high fission [[Nuclear cross section|cross section]], and is quickly destroyed if it is produced in a nuclear reactor. It has been investigated whether this isotope could be used for a novel type of [[nuclear rocket]].<ref name="Am242-sciencedaily">{{cite press release |url=https://www.sciencedaily.com/releases/2001/01/010103073253.htm |title=Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks |date=December 28, 2000 |publisher=Ben-Gurion University Of The Negev}}</ref><ref name="Ronen">{{cite journal|last1=Ronen|first1=Yigal|last2=Shwageraus|first2=E.|title=Ultra-thin 241mAm fuel elements in nuclear reactors|journal=Nuclear Instruments and Methods in Physics Research A|date=2000|volume=455|issue=2|pages=442–451|doi=10.1016/s0168-9002(00)00506-4|bibcode=2000NIMPA.455..442R}}</ref>

{| class="wikitable"
|+{{sup|242}}Am decay modes ([[half-life]]: 16 hours){{NUBASE2020|ref}}
!Probability!!Decay mode!![[Decay energy]]!![[Decay product]]
|-
|82.7%||[[beta decay]]||0.664&nbsp;MeV ||{{sup|242}}[[Curium|Cm]]
|-
|17.3%||[[electron capture]]||0.751&nbsp;MeV ||[[Plutonium-242|{{sup|242}}Pu]]
|}

===Americium-243===
[[File:Am243.png|thumb|A sample of Am-243|130px]]
'''Americium-243''' has a mass of 243.06138&nbsp;g/mol and a [[half-life]] of 7350 years{{NUBASE2020|ref}}, the longest lasting of all americium isotopes. It is formed in the [[nuclear fuel cycle]] by [[neutron capture]] on [[plutonium-242]] followed by [[beta decay]].<ref name="243Am-ornl">[http://www.ornl.gov/sci/isotopes/r_am243.html "Americium-243"] {{webarchive|url=https://web.archive.org/web/20110225120159/http://www.ornl.gov/sci/isotopes/r_am243.html |date=2011-02-25 }}. Oak Ridge National Laboratory. Retrieved 25 December 2009.</ref> Production increases exponentially with increasing [[burnup]] as a total of 5 neutron captures on [[uranium-238|{{sup|238}}U]] are required. If [[MOX-fuel]] is used, particularly MOX-fuel high in {{chem|241|Pu}} and {{chem|242|Pu}}, more americium overall and more {{chem|243|Am}} will be produced.

It decays by either emitting an [[alpha particle]] (with a decay energy of 5.27&nbsp;MeV)<ref name="243Am-ornl"/> to become {{sup|239}}Np, which then quickly decays to [[plutonium-239|{{sup|239}}Pu]], or rarely, by [[spontaneous fission]].<ref name="243Am-jlab">[http://education.jlab.org/itselemental/iso095.html "Isotopes of the Element Americium"]. Jefferson Lab Science Education. Retrieved 25 December 2009.</ref>

As for the other americium isotopes, and more generally for all alpha emitters, {{sup|243}}Am is [[carcinogen]]ic in case of internal contamination after being inhaled or ingested. {{sup|243}}Am also presents a risk of external irradiation associated with the gamma ray emitted by its short-lived decay product [[neptunium-239|{{sup|239}}Np]]. The external irradiation risk for the other two americium isotopes ({{sup|241}}Am and {{sup|242m}}Am) is less than 10% of that for americium-243.<ref name="anl"/>

== References ==
{{reflist|30em}}

== Sources ==
* Isotope masses from:
** {{NNDC}}
* Half-life, spin, and isomer data selected from the following sources.
** {{NNDC}}
**IAEA - Nuclear Data Section. [https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html Live Chart of Nuclides.] Vienna International Centre.
** {{CRC85|chapter=11}}

{{Navbox element isotopes}}

[[Category:Isotopes of americium| ]]
[[Category:Americium]]
[[Category:Lists of isotopes by element|Americium]]