Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 73 Ta 180 179.9474648(24) 0.0001201(32) 180.94788(2) 181 180.9479958(20) 0.9998799(32) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page