Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 88 Ra 223 223.0185023(27) [226] 224 224.0202120(23) 226 226.0254103(25) 228 228.0310707(26) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page