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Isotopes of Fermium

List, data and properties of all known isotopes of Fermium as well as radioactive decay products and intermediate products.

 

Fermium isotopes

All of the atomic nuclei of the chemical element fermium are summarized under fermium isotopes; these consist of an atomic nucleus with 100 protons and in the uncharged state of 100 electrons. The difference between the individual fermium isotopes lies in the number of neutrons in the nucleus - and thus in the mass number.

The artificial chemical element fermium does not have any stable isotopes. Fermium-255 was the first nuclide to be discovered during a nuclear weapon test in 1952.

To date, a total of 19 different fermium isotopes have been artificially produced and characterized. Fermium-257 has the longest half-life at 100.5 days.

 

Isotope Table: Fermium

 

Atomic Properties

Isotope
Nuclide
ZANNameAtomic Mass
[Nuclear Mass]
{Mass Excess}
Spin I
(h/2π)
μParent
123456789
241Fm100241141Fermium-241241.07421(32) u
[241.0193601 u]
{69.12617 MeV}
242Fm100242142Fermium-242242.07343(43) u
[242.0185801 u]
{68.3996 MeV}
0+
243Fm100243143Fermium-243243.07449(23) u
[243.0196401 u]
{69.38699 MeV}
(7/2+)
244Fm100244144Fermium-244244.07404(22) u
[244.0191901 u]
{68.96782 MeV}
0+
245Fm100245145Fermium-245245.07535(21) u
[245.0205001 u]
{70.18807 MeV}
1/2+~
246Fm100246146Fermium-246246.075351(16) u
[246.0205011 u]
{70.189 MeV}
0+
247Fm100247147Fermium-247247.07694(12) u
[247.0220901 u]
{71.66915 MeV}
(7/2+)251No
247mFm100247147Fermium-247m247.07694(12) u
[247.0220901 u]
{71.66915 MeV}
(1/2+)
248Fm100248148Fermium-248248.077186(9) u
[248.0223361 u]
{71.8983 MeV}
0+252No
248mFm100248148Fermium-248m248.077186(9) u
[248.0223361 u]
{71.8983 MeV}
249Fm100249149Fermium-249249.078926(7) u
[249.0240761 u]
{73.5191 MeV}
(7/2+)253No
250Fm100250150Fermium-250250.079520(8) u
[250.0246701 u]
{74.0724 MeV}
0+254No
250Md
250mFm100250150Fermium-250m250.079520(8) u
[250.0246701 u]
{74.0724 MeV}
251Fm100251151Fermium-251251.081540(16) u
[251.0266901 u]
{75.95402 MeV}
(9/2-)255No
251mFm100251151Fermium-251m251.081540(16) u
[251.0266901 u]
{75.95402 MeV}
5/2+
252Fm100252152Fermium-252252.082465(6) u
[252.0276151 u]
{76.81565 MeV}
0+256No
253Fm100253153Fermium-253253.085181(3) u
[253.0303311 u]
{79.34559 MeV}
1/2+257No
254Fm100254154Fermium-254254.0868527(26) u
[254.0320028 u]
{80.90277 MeV}
0+254Es
255Fm100255155Fermium-255255.089963(5) u
[255.0351131 u]
{83.79999 MeV}
7/2+-3.46255Es
255Md
259No
256Fm100256156Fermium-256256.091774(6) u
[256.0369241 u]
{85.48693 MeV}
0+256Es
256Md
257Fm100257157Fermium-257257.095105(5) u
[257.0402551 u]
{88.58974 MeV}
(9/2+)257Es
257Md
258Fm100258158Fermium-258258.09708(21) u
[258.0422301 u]
{90.42944 MeV}
0+258Md
259Fm100259159Fermium-259259.1006(3) u
[259.0457501 u]
{93.7083 MeV}

 

Radioactive Decay Properties

IsotopeRadioactive DecayAEExtern
Half-lifeDecay ModeProbabilityEnergy
1101112131415
Fm-2410.73(6) msSF div
EC → 241Es
α → 237Cf
> 78 %
< 12 %

5.26(37) MeV
8.76(31) MeV
AL
Fm-2420.8(2) msSF div≤ 100 %AL
Fm-243231(9) msα → 239Cf
EC/β+243Es
SF div
91(3) %
< 10 %
9(1) %
8.69(50) MeV
4.64(30) MeV
AL
Fm-2443.12(8) msSF div
EC → 244Es
α → 240Cf
> 97 %
< 2 %
< 1 %

2.94(27) MeV
8.55(20) MeV
AL
Fm-2454.2(13) sα → 241Cf≤ 100 %8.44(10) MeVAL
Fm-2461.54(4) sα → 242Cf
EC → 246Es
SF div
93.2(6) %
≤ 1.3 %
6.8(6) %
8.377(8) MeV
2.29(22) MeV
AL
Fm-24731(1) sα → 243Cf
EC/β+247Es
64 %
36 %
8.258(10) MeV
3.09(12) MeV
AL
Fm-247m5.1(2) sα → 243Cf
Iso → 247Fm
88(2) %
12(2) %

45(7) keV
Fm-24834.5(12) sα → 244Cf
EC → 248Es
SF div
95(5) %
5(5) %
0.10(5) %
7.995(8) MeV
1.60(50) MeV
AL
Fm-248m10.1(6) ms1074 keV
Fm-2492.6(7) minα → 245Cf
EC/β+249Es
33(9) %
67(9) %
7.709(6) MeV
2.34(3) MeV
AL
Fm-25030(3) minα → 246Cf
EC → 250Es
SF div
> 90 %
< 10 %
0.069(10) %
7.557(8) MeV
0.85(10) MeV
AL
Fm-250m1.8(1) sIso → 250Fm
α → 246Cf
EC/β+250Es
SF div
>= 80 %
< 20 %
? %
< 0.0008 %



+x keVAL
Fm-2515.30(8) hα → 247Cf
EC/β+251Es
1.80(13) %
98.20(13) %
7.4251(20) MeV
1.442(16) MeV
AL
Fm-251m21.1(19) μs100.0(1) keVAL
Fm-25225.39(4) hα → 248Cf
SF div
99.9977(2) %
0.0023(2) %
7.1527(20) MeV
AL
Fm-2533.00(12) dα → 249Cf
EC → 253Es
12(1) %
88(1) %
71980(27) MeV
0.335(3) MeV
AL
Fm-2543.240(2) hα → 250Cf
SF div
99.9408(3) %
0.0592(3) %
7.3075(19) MeV
AL
Fm-25520.07(7) hα → 251Cf
SF div
< 100 %
> 0 %
7.2397(18) MeV
AL
Fm-256157.1(13) minα → 252Cf
SF div
8.1(3) %
91.9(3) %
7.027(5) MeV
AL
Fm-257100.5(2) dα → 253Cf
SF div
99.790(4) %
0.210(4) %
6.8635(14) MeV
AL
Fm-258370(14) μsSF div≤ 100 %AL
Fm-2591.5(2) sSF div100 %AL

 

Notes (related to the columns):

1 - nuclide, isotope symbol.
2 - Z = number of protons (atomic number).
3 - Mass number A.
4 - N = number of neutrons.
5 - Identification of the Fermium isotope.
6 - Relative atomic mass of the Fermium isotope (isotopic mass including electrons) and the mass of the atomic nucleus in square brackets (nuclear mass, nuclide mass without electrons), each related to 12C = 12.00000 [2]. In addition, the mass excess is given in MeV.
7 - Nuclear spin I, unit: h/2π.
8 - Nuclear magnetic moment μmag.
9 - Source nuclides: Possible, assumed or actual source nuclides (mother nuclides, parent nuclides). If applicable, the corresponding decay modes can be found in the data for the respective starting nuclide.
10 - Decay: Half-live of the Fermium isotope (a = years; ; d = days; h = hours; min = minutes; s = seconds).
11 - Decay: type of decay into the respective daughter nuclides with n = neutron emission; p = proton emission; α = alpha decay; β- = beta minus decay with electron emission; EC = electron capture; β+ = positron emission; ε = β+ and/or EC; Iso = isomeric transition; CD = cluster decay; SF = spontaneous decay.
12 - Decay percentage in percent (%).
13 - Decay energy; Particle energy related to decay type.
14 - AE = Excitation energy for metastable nuclei.
15 - Other information and notes: AL = Adopted Levels (link to external data [1]).

Miscellaneous:

()- Numbers in brackets: uncertainty to represent the spread of the reported value.
~ - Theoretical values or systematic trends.
  - unlisted-: Nuclides that have already been mentioned in the literature but for some reason can no longer be found in the current nuclide tables because their discovery e.g. has not confirmed.

 

Radiation Protection

According to the Radiation Protection Ordinance (StrlSchV 2018, Germany), the following values (columns 1 to 7) apply to the handling of Fermium radionuclides:

NuclideLimit ValueHASS limitSCDaughter NuclidesHalf-life
Fm-252106 Bq1000 Bq/g25.4 h
Fm-253106100 Bq/g3.0 d
Fm-254107 Bq10000 Bq/g100 Bq cm-23.2 h
Fm-255106 Bq100 Bq/g10 Bq cm-220.1 h
Fm-257105 Bq1 Bq/g100.5 d

(HASS = High-Activity Sealed Radioactive Sources; SC = surface contamination)

 

Literature Sources and References

Properties of the Fermium nucleides

[1] - NuDat: National Nuclear Data Center, Brookhaven National Laboratory, based on ENSDF and the Nuclear Wallet Cards.

[2] - G. Audi et. al.: The NUBASE evaluation of nuclear and decay properties. Nuclear Physics, (2003), DOI 10.1016/j.nuclphysa.2003.11.001.

[3] - Live Chart of Nuclides. Nuclear structure and decay data.

Fermium: NMR properties

[4] - N. J. Stone: Table of nuclear magnetic dipole and electric quadrupole moments. Atomic Data and Nuclear Data Tables, (2005), DOI 10.1016/j.adt.2005.04.001.

[5] - Pekka Pyykkö: Year-2008 nuclear quadrupole moments. Molecular Physics, (2008), DOI 10.1080/00268970802018367.

[6] - Pekka Pyykkö: Year-2017 nuclear quadrupole moments. Molecular Physics, (2018), DOI 10.1080/00268976.2018.1426131.

[7] - N. J. Stone: Table of recommended nuclear magnetic dipole moments. IAEA, (2019).

More sources:

[8] - Isotopic abundances, atomic weights and isotopic masses: see respective keyword.

 


Category: Isotopes

Last update: 05.07.2020



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