Fermium-256

Properties and data of the isotope ²⁵⁶Fm.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

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:156Isotopic mass:256.091774(6) u (atomic weight of Fermium-256)Nuclide mass:256.0369241 u (calculated nuclear mass without electrons)Mass excess:85.48693 MeVMass defect:2.042456096 u (per nucleus)Nuclear binding energy:1902.53559869 MeV (per nucleus)
7.43177968 MeV (average binding energy per nucleon)Separation energy:S_N = 6.384(7) MeV (first neutron)
S_P = 5.891(12) MeV (first proton)Half-life:157.1(13) minDecay constant λ:7.353566524081 × 10^-5 s^-1Specific activity α:1.729852087145 × 10⁺¹⁷ Bq g^-1
4675275.9112051 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Year of discovery:1955

Radioactive Decay

Half-life T_½ = 157.1(13) min (minutes) respectively 9.426 × 10³ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁵²Cf	8.1(3) %	7.027(5) MeV
SZ	div	91.9(3) %

Parent Nuclides

Direct parent isotopes are: ²⁵⁶Es, ²⁵⁶Md.

Isotones and Isobars

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.

Z	Isotone N = 156	Isobar A = 256
96	²⁵²Cm
97	²⁵³Bk
98	²⁵⁴Cf	²⁵⁶Cf
99	²⁵⁵Es	²⁵⁶Es
100	²⁵⁶Fm	²⁵⁶Fm
101	²⁵⁷Md	²⁵⁶Md
102	²⁵⁸No	²⁵⁶No
103	²⁵⁹Lr	²⁵⁶Lr
104	²⁶⁰Rf	²⁵⁶Rf
105	²⁶¹Db	²⁵⁶Db
106	²⁶²Sg
107	²⁶³Bh
108	²⁶⁴Hs