Iron-57
Properties and data of the isotope 57Fe.
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
Parent Nuclides
Direct parent isotopes are: 57Co, 57Mn.
Occurrence
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 | 53.939609(3) u | 5.845(105) % | stable | 0+ |
| Isotope 56Fe | 55.934936(3) u | 91.754(106) % | stable | 0+ |
| Isotope 58Fe | 57.933274(3) u | 0.282(12) % | stable | 0+ |
| Isotope 57Fe | 56.93539195(29) u | 2.119(29) % | stable | 1/2- |
NMR data
Nuclear magnetic properties and parameters of the NMR active Nuclide 57Fe
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.
| Z | Isotone N = 31 | Isobar A = 57 |
|---|
| 15 | 46P | |
| 16 | 47S | |
| 17 | 48Cl | |
| 18 | 49Ar | |
| 19 | 50K | 57K |
| 20 | 51Ca | 57Ca |
| 21 | 52Sc | 57Sc |
| 22 | 53Ti | 57Ti |
| 23 | 54V | 57V |
| 24 | 55Cr | 57Cr |
| 25 | 56Mn | 57Mn |
| 26 | 57Fe | 57Fe |
| 27 | 58Co | 57Co |
| 28 | 59Ni | 57Ni |
| 29 | 60Cu | 57Cu |
| 30 | 61Zn | 57Zn |
| 31 | 62Ga | |
| 32 | 63Ge | |
| 33 | 64As | |
| 34 | 65Se | |
| 35 | 66Br | |
| 36 | 67Kr | |
External data and identifiers
Literature and References
[1] - Francis William Aston:
The isotopic constitution and atomic weights of hafnium, thorium, rhodium, titanium, zirconium, calcium, gallium, silver, carbon, nickel, cadmium, iron and indium.
In: Proceedings A, 149, 867, (1935), DOI 10.1098/rspa.1935.0070.
Last update: 2026-01-14
Perma link: https://www.chemlin.org/isotope/iron-57
© 1996 - 2026 ChemLin
