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:Isotopes of fermium

{{Short description|none}}

{{Infobox fermium isotopes}}

Fermium (100Fm) 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 fallout from nuclear testing) was 255Fm in 1952. 250Fm was independently synthesized shortly after the discovery of 255Fm. There are 20 known radioisotopes ranging in atomic mass from 241Fm to 260Fm (260Fm is unconfirmed), and 4 nuclear isomers, 247mFm, 250mFm, 251mFm, and 253mFm. The longest-lived isotope is 257Fm with a half-life of 100.5 days, and the longest-lived isomer is 247mFm with a half-life of 5.1 seconds.

List of isotopes

{{Anchor|Fermium-253m1|Fermium-253m2}}

{{Isotopes table

|symbol=Fm

|refs=NUBASE2020, AME2020 II

|notes=m, unc(), mass#, spin(), spin#, SF, EC, IT

}}

|-

| rowspan=3|241Fm

| rowspan=3 style="text-align:right" | 100

| rowspan=3 style="text-align:right" | 141

| rowspan=3|241.07431(32)#

| rowspan=3|730(60) μs

| SF?

| (various)

| rowspan=3|5/2+#

|-

| α (<14%)

| 237Cf

|-

| β+ (<12%)

| 241Es

|-

| rowspan=2|242Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 142

| rowspan=2|242.07343(43)#

| rowspan=2|0.8(2) ms

| SF

| (various)

| rowspan=2|0+

|-

| α?

| 238Cf

|-

| rowspan=3|243Fm{{cite journal |last1=Khuyagbaatar |first1=J. |last2=Heßberger |first2=F. P. |last3=Hofmann |first3=S. |last4=Ackermann |first4=D. |last5=Burkhard |first5=H. G. |last6=Heinz |first6=S. |last7=Kindler |first7=B. |last8=Kojouharov |first8=I. |last9=Lommel |first9=B. |last10=Mann |first10=R. |last11=Maurer |first11=J. |last12=Nishio |first12=K. |title=α decay of Fm 243 143 and Fm 245 145 , and of their daughter nuclei |journal=Physical Review C |date=12 October 2020 |volume=102 |issue=4 |page=044312 |doi=10.1103/PhysRevC.102.044312 |s2cid=241259726 |url=https://journals.aps.org/prc/pdf/10.1103/PhysRevC.102.044312 |access-date=24 June 2023 |language=en |issn=2469-9985}}

| rowspan=3 style="text-align:right" | 100

| rowspan=3 style="text-align:right" | 143

| rowspan=3|243.07441(14)#

| rowspan=3|231(9) ms

| α (91%)

| 239Cf

| rowspan=3|(7/2−)

|-

| SF (9%)

| (various)

|-

| β+?

| 243Es

|-

| rowspan=3|244Fm

| rowspan=3 style="text-align:right" | 100

| rowspan=3 style="text-align:right" | 144

| rowspan=3|244.07404(22)#

| rowspan=3|3.12(8) ms

| SF (>97%)

| (various)

| rowspan=3|0+

|-

| β+ (<2%)

| 244Es

|-

| α (<1%)

| 240Cf

|-

| rowspan=3|245Fm{{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}}

| rowspan=3 style="text-align:right" | 100

| rowspan=3 style="text-align:right" | 145

| rowspan=3|245.07535(21)#

| rowspan=3|4.2(13) s

| α (88.5%)

| 241Cf

| rowspan=3|(1/2+)

|-

| β+ (11.5%)

| 245Es

|-

| SF (<0.3%)

| (various)

|-

| rowspan=3|246Fm

| rowspan=3 style="text-align:right" | 100

| rowspan=3 style="text-align:right" | 146

| rowspan=3|246.075350(17)

| rowspan=3|1.54(4) s

| α (93.2%)

| 242Cf

| rowspan=3|0+

|-

| SF (6.8%)

| (various)

|-

| EC (<1.3%)

| 246Es

|-

| rowspan=2|247Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 147

| rowspan=2|247.07694(19)#

| rowspan=2|31(1) s

| α (~64%)

| 243Cf

| rowspan=2|(7/2+)

|-

| β+? (~36%)

| 247Es

|-id=Fermium-247m

| rowspan=3 style="text-indent:1em" | 247mFm

| rowspan=3 colspan="3" style="text-indent:2em" | 49(8) keV

| rowspan=3| 5.1(2) s

| α (88%)

| 243Cf

| rowspan=3|(1/2+)

|-

| IT?

| 247Fm

|-

| β+?

| 247Es

|-

| rowspan=3|248Fm

| rowspan=3 style="text-align:right" | 100

| rowspan=3 style="text-align:right" | 148

| rowspan=3|248.0771855(91)

| rowspan=3|34.5(12) s

| α (99.9%)

| 244Cf

| rowspan=3|0+

|-

| SF (0.1%)

| (various)

|-

| β+?

| 248Es

|-id=Fermium-248m

| rowspan=3 style="text-indent:1em" | 248mFm

| rowspan=3 colspan="3" style="text-indent:2em" | 1200(100)# keV

| rowspan=3| 10.1(6) ms

| IT?

| 248Fm

| rowspan=3|6+#

|-

| α?

| 244Cf

|-

| β+?

| 248Es

|-

| rowspan=2|249Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 149

| rowspan=2|249.0789260(67)

| rowspan=2|1.6(1) min

| β+? (67%)

| 249Es

| rowspan=2|7/2+

|-

| α (33%)

| 245Cf

|-

| rowspan=3|250Fm

| rowspan=3 style="text-align:right" | 100

| rowspan=3 style="text-align:right" | 150

| rowspan=3|250.0795198(85)

| rowspan=3|31.0(11) min

| α (99.99%)

| 246Cf

| rowspan=3|0+

|-

| SF (6.9×10−3%)

| (various)

|-

| EC?

| 250Es

|-id=Fermium-250m

| rowspan=4 style="text-indent:1em" | 250mFm

| rowspan=4 colspan="3" style="text-indent:2em" | 1199.2(10) keV

| rowspan=4|1.92(5) s

| IT

| 250Fm

| rowspan=4|(8−)

|-

| α?

| 246Cf

|-

| β+?

| 250Es

|-

| SF?

| (various)

|-

| rowspan=2|251Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 151

| rowspan=2|251.081545(15)

| rowspan=2|5.30(8) 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) keV

| 21.8(8) μs

| IT

| 251Fm

| 5/2+

|-

| rowspan=2|252Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 152

| rowspan=2|252.0824660(56)

| rowspan=2|25.39(4) h

| α (99.99%){{refn|group=n|Theoretically capable of β+β+ decay to 252Cf}}

| 248Cf

| rowspan=2|0+

|-

| SF (.0023%)

| (various)

|-

| rowspan=2|253Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 153

| rowspan=2|253.0851809(16)

| rowspan=2|3.00(12) 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) keV

| 0.56(6) μs

| IT

| 253Fm

| 11/2-#

|-

| rowspan=2|254Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 154

| rowspan=2|254.0868524(20)

| rowspan=2|3.240(2) h

| α (99.94%)

| 250Cf

| rowspan=2|0+

|-

| SF (0.0592%)

| (various)

|-

| rowspan=2|255Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 155

| rowspan=2|255.0899635(42)

| rowspan=2|20.07(7) h

| α

| 251Cf

| rowspan=2|7/2+

|-

| SF (2.4×10−5%)

| (various)

|-

| rowspan=2|256Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 156

| rowspan=2|256.0917717(32)

| rowspan=2|157.1(13) min

| SF (91.9%)

| (various)

| rowspan=2|0+

|-

| α (8.1%)

| 252Cf

|-

| rowspan=2|257FmHeaviest nuclide produced via neutron capture

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 157

| rowspan=2|257.0951054(47)

| rowspan=2|100.5(2) d

| α (99.79%)

| 253Cf

| rowspan=2|9/2+

|-

| SF (.210%)

| (various)

|-

| rowspan=2|258Fm

| rowspan=2 style="text-align:right" | 100

| rowspan=2 style="text-align:right" | 158

| rowspan=2|258.09708(22)#

| rowspan=2|370(14) μs

| SF

| (various)

| rowspan=2|0+

|-

| α?

| 254Cf

|-id=Fermium-259

| 259Fm

| style="text-align:right" | 100

| style="text-align:right" | 159

| 259.10060(30)#

| 1.5(2) s

| SF

| (various)

| 3/2+#

|-id=Fermium-260

| 260FmDiscovery of this isotope is unconfirmedNot directly synthesized, occurs as decay product of 260Md

| style="text-align:right" | 100

| style="text-align:right" | 160

| 260.10281(47)#

| 1# min

| SF

| (various)

| 0+

{{Isotopes table/footer}}

Chronology of isotope discovery

class="wikitable"

! Isotope !! Discovered !! Reaction

id=Fermium-241

| 241Fm

2008204Pb(40Ar,3n)
id=Fermium-242

| 242Fm

1975204Pb(40Ar,2n), 206Pb(40Ar,4n)
id=Fermium-243

| 243Fm

1981206Pb(40Ar,3n)
id=Fermium-244

| 244Fm

1967233U(16O,5n)
id=Fermium-245

| 245Fm

1967233U(16O,4n)
id=Fermium-246

| 246Fm

1966235U(16O,5n)
id=Fermium-247

| 247Fm

1967239Pu(12C,4n)
id=Fermium-248

| 248Fm

1958240Pu(12C,4n)
id=Fermium-249

| 249Fm

1960238U(16O,5n)
id=Fermium-250

| 250Fm

1954238U(16O,4n)
id=Fermium-251

| 251Fm

1957249Cf(α,2n)
id=Fermium-252

| 252Fm

1956249Cf(α,n)
id=Fermium-253

| 253Fm

1957252Cf(α,3n)
id=Fermium-254

| 254Fm

1954Neutron capture
id=Fermium-255

| 255Fm

1954Neutron capture
id=Fermium-256

| 256Fm

1955Neutron capture
id=Fermium-257

| 257Fm

1964Neutron capture
id=Fermium-258

| 258Fm

1971257Fm(d,p)
id=Fermium-259

| 259Fm

1980257Fm(t,p)
id=Fermium-260

| 260Fm?

1992?254Es+18O, 22Ne — transfer (EC of 260Md)

260Fm was not confirmed in 1997.

References

{{Reflist}}

  • Isotope masses from:
  • {{cite journal |author=M. Wang |author2=G. Audi |author3=A. H. Wapstra |author4=F. G. Kondev |author5=M. MacCormick |author6=X. Xu|year=2012 |title=The AME2012 atomic mass evaluation (II). Tables, graphs and references. |url=http://amdc.in2p3.fr/masstables/Ame2012/Ame2012b-v2.pdf |journal=Chinese Physics C |volume=36 |issue= 12 |pages=1603–2014 |doi=10.1088/1674-1137/36/12/003|bibcode = 2012ChPhC..36....3M |s2cid=250839471 |display-authors=etal}}
  • {{NUBASE 2003}}
  • Half-life, spin, and isomer data selected from the following sources.
  • {{NUBASE 2012}}
  • {{NUBASE 2003}}
  • {{NNDC}}
  • {{CRC85|chapter=11}}
  • {{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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