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Isotopes of Fermium

List, data and properties of all known isotopes of Fermium.

Content
Atomic properties
Decay properties
NMR active nuclides
Radiation protection
References
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

The two following tables list the most important data and properties of the Fermium isotopes. Further information on the individual Fermium isotopes is listed on separate pages and can be accessed via the link in column 1.

 

Atomic Properties

Isotope
Nuclide		ENAtomic Mass
[Nuclear Mass]
{Mass Excess}		Spin I
(h/2π)		Parent
123456
Fermium-241241100Fm141241.07421(32) u
[241.0193601 u]
{69.12617 MeV}
Fermium-242242100Fm142242.07343(43) u
[242.0185801 u]
{68.3996 MeV}		0+
Fermium-243243100Fm143243.07449(23) u
[243.0196401 u]
{69.38699 MeV}		(7/2+)
Fermium-244244100Fm144244.07404(22) u
[244.0191901 u]
{68.96782 MeV}		0+
Fermium-245245100Fm145245.07535(21) u
[245.0205001 u]
{70.18807 MeV}		1/2+~
Fermium-246246100Fm146246.075351(16) u
[246.0205011 u]
{70.189 MeV}		0+
Fermium-247247100Fm147247.07694(12) u
[247.0220901 u]
{71.66915 MeV}		(7/2+)251No
Fermium-247m247m100Fm147247.07694(12) u
[247.0220901 u]
{71.66915 MeV}		(1/2+)
Fermium-248248100Fm148248.077186(9) u
[248.0223361 u]
{71.8983 MeV}		0+252No
Fermium-248m248m100Fm148248.077186(9) u
[248.0223361 u]
{71.8983 MeV}
Fermium-249249100Fm149249.078926(7) u
[249.0240761 u]
{73.5191 MeV}		(7/2+)253No
Fermium-250250100Fm150250.079520(8) u
[250.0246701 u]
{74.0724 MeV}		0+254No
250Md
Fermium-250m250m100Fm150250.079520(8) u
[250.0246701 u]
{74.0724 MeV}
Fermium-251251100Fm151251.081540(16) u
[251.0266901 u]
{75.95402 MeV}		(9/2-)255No
Fermium-251m251m100Fm151251.081540(16) u
[251.0266901 u]
{75.95402 MeV}		5/2+
Fermium-252252100Fm152252.082465(6) u
[252.0276151 u]
{76.81565 MeV}		0+256No
Fermium-253253100Fm153253.085181(3) u
[253.0303311 u]
{79.34559 MeV}		1/2+257No
Fermium-254254100Fm154254.0868527(26) u
[254.0320028 u]
{80.90277 MeV}		0+254Es
Fermium-255255100Fm155255.089963(5) u
[255.0351131 u]
{83.79999 MeV}		7/2+255Es
255Md
259No
Fermium-256256100Fm156256.091774(6) u
[256.0369241 u]
{85.48693 MeV}		0+256Es
256Md
Fermium-257257100Fm157257.095105(5) u
[257.0402551 u]
{88.58974 MeV}		(9/2+)257Es
257Md
Fermium-258258100Fm158258.09708(21) u
[258.0422301 u]
{90.42944 MeV}		0+258Md
Fermium-259259100Fm159259.1006(3) u
[259.0457501 u]
{93.7083 MeV}

 

Radioactive Decay Properties

IsotopeRadioactive DecayExtern
Half-lifeDecay ModeProbabilityEnergy
789101112
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) %
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) ms
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 %
0.0069(10) %		7.557(8) MeV
0.847(100) MeV
AL
Fm-250m1.8(1) sIso → 250Fm
α → 246Cf
EC/β+ → 250Es
SF div		>= 80 %
< 20 %
? %
< 0.0008 %


AL
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) μsAL
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 - name of the nuclide, isotope.
2 - E: isotope symbol with mass number (superscript; number of nucleons) and atomic number (subscript; number of protons).
3 - N: number of neutrons.
4 - 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.
5 - nuclear spin I, unit: h/2π.
6 - 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.

7 - isotope notation in short form.
8 - decay: half-live of the Fermium isotope (a = years; ; d = days; h = hours; min = minutes; s = seconds).
9 - decay mode: 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.
10 - decay probability in percent (%).
11 - decay energy; Particle energy related to decay type.
12 - 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.

 

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Last update: 2022-12-12

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