Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 14 Si 28 27.97692653465(44) 0.92223(19) [28.084,28.086] 29 28.97649466490(52) 0.04685(8) 30 29.973770136(23) 0.03092(11) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page