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Natural iron (26 Fe) consists of four stable isotopes: 5.845% 54 Fe (possibly radioactive with half-life > 4.4 × 10 20 years), [4] 91.754% 56 Fe, 2.119% 57 Fe and 0.286% 58 Fe. There are 28 known radioisotopes and 8 nuclear isomers, the most stable of which are 60 Fe (half-life 2.6 million years) and 55 Fe (half-life 2.7 years).
However, this does not hold true for all atoms. Iron's most common isotope has a mass number of 56, while the stable isotopes of iron vary in mass number from 54 to 58. Monoisotopic mass is typically expressed in daltons (Da), also called unified atomic mass units (u).
The rarer isotopes nickel-62 and iron-58, which both have higher binding energies, are not shown. Iron-56 (56 Fe) is the most common isotope of iron. About 91.754% of all iron is iron-56. Of all nuclides, iron-56 has the lowest mass per nucleon. With 8.8 MeV binding energy per nucleon, iron-56 is one of the most tightly bound nuclei. [1]
At carbon, the ratio of mass (in daltons) to mass number is defined as 1, and after carbon it becomes less than one until a minimum is reached at iron-56 (with only slightly higher values for iron-58 and nickel-62), then increases to positive values in the heavy isotopes, with increasing atomic number.
Speculated approximate lower limit of the mass of a primordial black hole: 1.5 × 10 −8 kg: US RDA for vitamin D for adults [46] ~2 × 10 −8 kg Uncertainty in the mass of the International Prototype of the Kilogram (IPK) (±~20 μg) [47] 2.2 × 10 −8 kg Planck mass, [48] can be expressed as the mass of a 2 Planck Length radius black hole ...
The nominal mass is not always the lowest mass number, for example iron has isotopes 54 Fe, 56 Fe, 57 Fe, and 58 Fe with abundances 6%, 92%, 2%, and 0.3%, respectively, and a nominal mass of 56 Da.
Iron is a chemical element; it has the symbol Fe (from Latin ferrum 'iron') and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's outer and inner core.
26 Fe iron; use: 7.86 g/cm 3: WEL (near r.t.) ... 58 Ce cerium; use: 6.55 g/cm 3: CR2 (at m.p.) 6.55 g/cm 3: ... formula weight = 222 Notes