See also: List of individual Fermium isotopes (and general data sources).
General data
Name of the isotope:Fermium-256; Fm-256Symbol:256Fm or 256100FmMass number A:256 (= number of nucleons)Atomic number Z:100 (= number of protons)Neutrons N:156Nucleon pairing (Z - N):even - evenNuclear ratio (N/Z ratio):1.56 (= neutron-proton ratio)Neutron excess (N-Z):56Isotopic mass:256.091772(3) u (atomic weight of Fermium-256)Nuclide mass:256.0369221 u (calculated nuclear mass without electrons)Mass excess:85.486 MeVMass defect:2.042457096 u (per nucleus)Nuclear binding energy:1902.53653018 MeV (per nucleus) 7.43178332 MeV (average binding energy per nucleon)Separation energy:SN = 6.387(5) MeV (first neutron) SP = 5.893(11) MeV (first proton)Half-life:157.1(13) minDecay constant λ:7.353566524081 × 10-5 s-1Specific activity α:1.729232148978 × 10+17 Bq g-1 4673600.4026441 Ci g-1Spin and parity: (nuclear angular momentum)0+Year of discovery:1955
Radioactive Decay
Half-life T½ = 157.1(13) min (minutes) respectively 9.426 × 103 seconds s.
The following table shows the atomic nuclei that are isotonic (same neutron number N = 156) and isobaric (same nucleon number A = 256) with Fermium-256. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
