Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 26 Fe 54 53.93960899(53) 0.05845(35) 55.845(2) 56 55.93493633(49) 0.91754(36) 57 56.93539284(49) 0.02119(10) 58 57.93327443(53) 0.00282(4) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page