Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 7 N 14 14.00307400443(20) 0.99636(20) [14.00643,14.00728] 15 15.00010889888(64) 0.00364(20) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page