Iron-57 is a stable, naturally occuring isotope of the chemical element iron, which has 31 neutrons in its atomic nucleus in addition to the element-specific 26 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 57.
The discovery and mass determination of iron-57 using a spectrograph was reported in 1935 [1].
See also: List of individual Iron isotopes (and general data sources).
General data
Name of the isotope:Iron-57; Fe-57Symbol:57Fe or 5726FeMass number A:57 (= number of nucleons)Atomic number Z:26 (= number of protons)Neutrons N:31Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):1.1923076923077 (= neutron-proton ratio)Neutron excess (N-Z):5Isotopic mass:56.93539195(29) u (atomic weight of Iron-57)Nuclide mass:56.9211292 u (calculated nuclear mass without electrons)Mass excess:-60.18201 MeVMass defect:0.53667127799999 u (per nucleus)Nuclear binding energy:499.90607543 MeV (per nucleus) 8.77028203 MeV (average binding energy per nucleon)Separation energy:SN = 7.646172(17) MeV (first neutron) SP = 10.55932(21) MeV (first proton)Half-life:stableSpin and parity: (nuclear angular momentum)1/2-Isobaric spin: 5/2Magnetic dipole moment:μ(μN) = +0.09064(7)Charge radius:3.7532(17) femtometer fmYear of discovery:1935
Comparison of the natural Iron isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):
Atomic Mass ma
Quantity
Half-life
Spin
Iron Isotopic mixture
55.845 u
100 %
Isotope 54Fe
53.9396082(4) u
5.845(105) %
stable
0+
Isotope 56Fe
55.934936(3) u
91.754(106) %
stable
0+
Isotope 57Fe
56.93539195(29) u
2.119(29) %
stable
1/2-
Isotope 58Fe
57.933274(3) u
0.282(12) %
stable
0+
NMR data
Nuclear magnetic properties and parameters of the NMR active Nuclide57Fe
Isotope:57Fe-NMRQuantity:2.119(29) %Spin:1/2-Nuclearmagnetic moment μ/μN:+0.09064(7)Gyromagnetic ratio γ:0.8661 · 107 rad T-1 s-1 1.37844 MHz T-1Nuclear g-factor:gl = 0.18128Resonance frequency:v0 = 1.3816 MHz at 1 TRelative Sensitivity:[related to 1H = 1.000]: 0.0000341 (H0 = const.) 0.0324 (v0 = const.) 7.24 ยท 10-7 (at natural abundance) relative receptivity as compared to 13C: 0.00425 (at natural abundance) 0.201 (enriched)Reference compound: (conditions)Pure iron pentacarbonyl mixed with 20% Benzene-d6.Frequency ratio:Ξ(57Fe) = 3.237778 % [based on the reference substance]Chemical shift range:ca. 2600 ppm [-100 to +2500]
Isotones and Isobars
The following table shows the atomic nuclei that are isotonic (same neutron number N = 31) and isobaric (same nucleon number A = 57) with Iron-57. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
