Isotopes of fermium

{{Short description|none}} {{Infobox fermium isotopes}} Fermium ({{sub|100}}Fm) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be discovered (in nuclear fallout from the Ivy Mike H-bomb test) was {{sup|255}}Fm in 1952. {{sup|250}}Fm was independently synthesized (to establish priority if the former result had to remain classified) shortly after the discovery of {{sup|255}}Fm.

There are 20 known radioisotopes ranging in atomic mass from {{sup|241}}Fm to {{sup|260}}Fm ({{sup|260}}Fm is unconfirmed), and 5 nuclear isomers. The longest-lived isotope is {{sup|257}}Fm with a half-life of 100.5 days, and the longest-lived isomer is {{sup|247m}}Fm with a half-life of 5.1 seconds.

== List of isotopes == {{Anchor|Fermium-253m1|Fermium-253m2}}

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

{{Isotopes table |symbol=Fm |refs=NUBASE2020, AME2020 II, <!-- was updated 2024-09-25 --> IsotopeFRIB, IsomerFRIB |notes=m, unc(), mass#, spin(), spin#, SF, EC, IT, discoveryname }} |-id=Fermium-241 | rowspan=3|²⁴¹Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 141 | rowspan=3|241.07431(32)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/241.pdf 2008] | rowspan=3|{{val|730|(60)|u=us}} | SF | (various) | rowspan=3|5/2+# |- | α (<14%) | ²³⁷Cf |- | β⁺ (<12%) | ²⁴¹Es |-id=Fermium-242 | ²⁴²Fm | style="text-align:right" | 100 | style="text-align:right" | 142 | 242.07343(43)# | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/242.pdf 1975] | {{val|0.8|(2)|u=ms}} | SF | (various) | 0+ |-id=Fermium-243 | rowspan=2|²⁴³Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 143 | rowspan=2|243.07441(14)# | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/243.pdf 1981] | rowspan=2|{{val|231|(9)|u=ms}} | α (91%) | ²³⁹Cf | rowspan=2|7/2−# |- | SF (9%) | (various) |-id=Fermium-244 | rowspan=3|²⁴⁴Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 144 | rowspan=3|244.07404(22)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/244.pdf 1967] | rowspan=3|{{val|3.12|(8)|u=ms}} | SF (>97%) | (various) | rowspan=3|0+ |- | β⁺ (<2%) | ²⁴⁴Es |- | α (<1%) | ²⁴⁰Cf |-id=Fermium-245 | rowspan=3|²⁴⁵Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 145 | rowspan=3|245.07535(21)# | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/245.pdf 1967] | rowspan=3|{{val|4.2|(13)|u=s}} | α (88.5%) | ²⁴¹Cf | rowspan=3|1/2+# |- | β⁺ (11.5%)<ref>{{cite journal |last1=Tezekbayeva |first1=M. S. |last2=Yeremin |first2=A. V. |last3=Svirikhin |first3=A. I. |last4=Lopez-Martens |first4=A. |last5=Chelnokov |first5=M. L. |last6=Chepigin |first6=V. I. |last7=Isaev |first7=A. V. |last8=Izosimov |first8=I. N. |last9=Karpov |first9=A. V. |last10=Kuznetsova |first10=A. A. |last11=Malyshev |first11=O. N. |last12=Mukhin |first12=R. S. |last13=Popeko |first13=A. G. |last14=Popov |first14=Yu. A. |last15=Rachkov |first15=V. A. |last16=Sailaubekov |first16=B. S. |last17=Sokol |first17=E. A. |last18=Hauschild |first18=K. |last19=Jacob |first19=H. |last20=Chakma |first20=R. |last21=Dorvaux |first21=O. |last22=Forge |first22=M. |last23=Gall |first23=B. |last24=Kessaci |first24=K. |last25=Andel |first25=B. |last26=Antalic |first26=S. |last27=Bronis |first27=A. |last28=Mosat |first28=P. |title=Study of the production and decay properties of neutron-deficient nobelium isotopes |journal=The European Physical Journal A |date=24 March 2022 |volume=58 |issue=3 |pages=52 |doi=10.1140/epja/s10050-022-00707-9 |arxiv=2203.15659 |bibcode=2022EPJA...58...52T |s2cid=247720708 |url=https://link.springer.com/article/10.1140/epja/s10050-022-00707-9 |access-date=24 June 2023 |language=en |issn=1434-601X}}</ref> | ²⁴⁵Es |- | SF (<0.3%) | (various) |-id=Fermium-246 | rowspan=3|²⁴⁶Fm | rowspan=3 style="text-align:right" | 100 | rowspan=3 style="text-align:right" | 146 | rowspan=3|246.075353(15) | rowspan=3 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/246.pdf 1966] | rowspan=3|{{val|1.54|(4)|u=s}} | α (93.2%) | ²⁴²Cf | rowspan=3|0+ |- | SF (6.8%) | (various) |- | EC (<1.3%) | ²⁴⁶Es |-id=Fermium-247 | rowspan=2|²⁴⁷Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 147 | rowspan=2|247.07694(19)# | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/247.pdf 1967] | rowspan=2|{{val|31|(1)|u=s}} | α (~64%) | ²⁴³Cf | rowspan=2|(7/2+) |- | β⁺? (~36%) | ²⁴⁷Es |-id=Fermium-247m | rowspan=2 style="text-indent:1em" | ^247mFm | rowspan=2 colspan="3" style="text-indent:2em" | 49(8)&nbsp;keV | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/100/247Fm-1.pdf 1967] | rowspan=2| {{val|5.1|(2)|u=s}} | α (88%) | ²⁴³Cf | rowspan=2|(1/2+) |- | IT? (12%) | ²⁴⁷Fm |-id=Fermium-248 | rowspan=2|²⁴⁸Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 148 | rowspan=2|248.077185(9) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/248.pdf 1958] | rowspan=2|{{val|34.5|(12)|u=s}} | α (99.9%) | ²⁴⁴Cf | rowspan=2|0+ |- | SF (0.1%) | (various) |-id=Fermium-248m | rowspan=3 style="text-indent:1em" | ^248mFm | rowspan=3 colspan="3" style="text-indent:2em" | 1200(100)#&nbsp;keV | rowspan=3 style="text-align:center" | (2010)<ref group="n">Only published in a conference proceeding and not a refereed journal</ref> | rowspan=3| {{val|10.1|(6)|u=ms}} | IT? | ²⁴⁸Fm | rowspan=3|6+# |- | α? | ²⁴⁴Cf |- | β⁺? | ²⁴⁸Es |-id=Fermium-249 | rowspan=2|²⁴⁹Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 149 | rowspan=2|249.078926(7) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/249.pdf 1959] | rowspan=2|{{val|1.6|(1)|u=min}} | β⁺? (67%) | ²⁴⁹Es | rowspan=2|7/2+ |- | α (33%) | ²⁴⁵Cf |-id=Fermium-250 | rowspan=2|²⁵⁰Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 150 | rowspan=2|250.079520(8) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/250.pdf 1954] | rowspan=2|{{val|31.0|(11)|u=min}} | α (99.99%) | ²⁴⁶Cf | rowspan=2|0+ |- | SF (6.9×10⁻³%) | (various) |-id=Fermium-250m | style="text-indent:1em" | ^250mFm | colspan="3" style="text-indent:2em" | 1199.2(10)&nbsp;keV | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/100/250Fm-1.pdf 1971] | {{val|1.92|(5)|u=s}} | IT | ²⁵⁰Fm | (8−) |-id=Fermium-251 | rowspan=2|²⁵¹Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 151 | rowspan=2|251.081545(15) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/251.pdf 1957] | rowspan=2|{{val|5.30|(8)|u=h}} | β⁺ (98.20%) | ²⁵¹Es | rowspan=2|9/2− |- | α (1.80%) | ²⁴⁷Cf |-id=Fermium-251m | style="text-indent:1em" | ^251mFm | colspan="3" style="text-indent:2em" | 200.0(1)&nbsp;keV | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/100/251Fm-1.pdf 2006] | {{val|21.8|(8)|u=us}} | IT | ²⁵¹Fm | 5/2+ |-id=Fermium-252 | rowspan=2|²⁵²Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 152 | rowspan=2|252.082466(6) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/252.pdf 1956] | rowspan=2|{{val|25.39|(4)|u=h}} | α (99.99%){{refn|group=n|Theoretically capable of β⁺β⁺ decay to ²⁵²Cf}} | ²⁴⁸Cf | rowspan=2|0+ |- | SF (0.0023%) | (various) |-id=Fermium-253 | rowspan=2|²⁵³Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 153 | rowspan=2|253.0851809(17) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/253.pdf 1957] | rowspan=2|{{val|3.00|(12)|u=d}} | EC (88%) | ²⁵³Es | rowspan=2|1/2+ |- | α (12%) | ²⁴⁹Cf |-id=Fermium-253m | style="text-indent:1em" | ^253mFm | colspan="3" style="text-indent:2em" | 351(6)&nbsp;keV | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/isomers/abstracts/100/253Fm-1.pdf 2011] | {{val|0.56|(6)|u=us}} | IT | ²⁵³Fm | 11/2−# |-id=Fermium-254 | rowspan=2|²⁵⁴Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 154 | rowspan=2|254.0868524(20) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/254.pdf 1954] | rowspan=2|{{val|3.240|(2)|u=h}} | α (99.94%) | ²⁵⁰Cf | rowspan=2|0+ |- | SF (0.0592%) | (various) |-id=Fermium-255 | rowspan=2|²⁵⁵Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 155 | rowspan=2|255.089963(4) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/255.pdf 1954] | rowspan=2|{{val|20.07|(7)|u=h}} | α | ²⁵¹Cf | rowspan=2|7/2+ |- | SF (2.4×10⁻⁵%) | (various) |-id=Fermium-256 | rowspan=2|²⁵⁶Fm | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 156 | rowspan=2|256.091772(3) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/256.pdf 1955] | rowspan=2|{{val|157.1|(13)|u=min}} | SF (91.9%) | (various) | rowspan=2|0+ |- | α (8.1%) | ²⁵²Cf |-id=Fermium-257 | rowspan=2|²⁵⁷Fm<ref group="n">Heaviest nuclide produced via neutron capture</ref> | rowspan=2 style="text-align:right" | 100 | rowspan=2 style="text-align:right" | 157 | rowspan=2|257.095105(5) | rowspan=2 style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/257.pdf 1964] | rowspan=2|{{val|100.5|(2)|u=d}} | α (99.79%) | ²⁵³Cf | rowspan=2|9/2+ |- | SF (0.210%) | (various) |-id=Fermium-258 | ²⁵⁸Fm | style="text-align:right" | 100 | style="text-align:right" | 158 | 258.09708(22)# | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/258.pdf 1971] | {{val|370|(14)|u=us}} | SF | (various) | 0+ |-id=Fermium-259 | ²⁵⁹Fm | style="text-align:right" | 100 | style="text-align:right" | 159 | 259.10060(30)# | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/259.pdf 1980] | {{val|1.5|(2)|u=s}} | SF | (various) | |-id=Fermium-260 | ²⁶⁰Fm<ref group="n" name="uc">Discovery of this isotope is unconfirmed</ref><ref group="n">Not directly synthesized, occurs as decay product of ²⁶⁰Md</ref> | style="text-align:right" | 100 | style="text-align:right" | 160 | 260.10281(47)# | style="text-align:center" | [https://www.nndc.bnl.gov/discovery/abstracts/100/260.pdf (1992)] | 1#&nbsp;min | SF | (various) | 0+ {{Isotopes table/footer}}

== Chronology of isotope discovery ==

{| class="wikitable" ! Isotope !! Discovered !! Reaction |-id=Fermium-241 | ²⁴¹Fm || 2008|| ²⁰⁴Pb(⁴⁰Ar,3n) |-id=Fermium-242 | ²⁴²Fm || 1975|| ²⁰⁴Pb(⁴⁰Ar,2n), ²⁰⁶Pb(⁴⁰Ar,4n) |-id=Fermium-243 | ²⁴³Fm|| 1981|| ²⁰⁶Pb(⁴⁰Ar,3n) |-id=Fermium-244 | ²⁴⁴Fm|| 1967|| ²³³U(¹⁶O,5n) |-id=Fermium-245 | ²⁴⁵Fm|| 1967|| ²³³U(¹⁶O,4n) |-id=Fermium-246 | ²⁴⁶Fm|| 1966|| ²³⁵U(¹⁶O,5n) |-id=Fermium-247 | ²⁴⁷Fm|| 1967|| ²³⁹Pu(¹²C,4n) |-id=Fermium-248 | ²⁴⁸Fm|| 1958|| ²⁴⁰Pu(¹²C,4n) |-id=Fermium-249 | ²⁴⁹Fm|| 1960|| ²³⁸U(¹⁶O,5n) |-id=Fermium-250 | ²⁵⁰Fm|| 1954|| ²³⁸U(¹⁶O,4n) |-id=Fermium-251 | ²⁵¹Fm|| 1957|| ²⁴⁹Cf(α,2n) |-id=Fermium-252 | ²⁵²Fm|| 1956|| ²⁴⁹Cf(α,n) |-id=Fermium-253 | ²⁵³Fm|| 1957|| ²⁵²Cf(α,3n) |-id=Fermium-254 | ²⁵⁴Fm|| 1954|| Neutron capture |-id=Fermium-255 | ²⁵⁵Fm|| 1954|| Neutron capture |-id=Fermium-256 | ²⁵⁶Fm|| 1955|| Neutron capture |-id=Fermium-257 | ²⁵⁷Fm|| 1964|| Neutron capture |-id=Fermium-258 | ²⁵⁸Fm|| 1971|| ²⁵⁷Fm(d,p) |-id=Fermium-259 | ²⁵⁹Fm|| 1980|| ²⁵⁷Fm(t,p) |-id=Fermium-260 | ²⁶⁰Fm?|| 1992?|| ²⁵⁴Es+¹⁸O, ²²Ne — transfer (EC of ²⁶⁰Md) |} ²⁶⁰Fm was not confirmed in 1997.

== References == {{Reflist}}

**{{cite journal |author=M. Thoennessen |year=2012 |title=Discovery of Isotopes of Elements with Z≥100 |arxiv=1203.2105 |doi=10.1016/j.adt.2012.03.003 |volume=99 |issue=3 |journal=Atomic Data and Nuclear Data Tables |pages=312–344|bibcode=2013ADNDT..99..312T |s2cid=94982856 }}

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Category:Isotopes of fermium Category:Fermium Fermium