Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 35 Br 79 78.9183376(14) 0.5069(7) [79.901,79.907] 81 80.9162897(14) 0.4931(7) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page