Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 68 Er 162 161.9287884(20) 0.00139(5) 167.259(3) g 164 163.9292088(20) 0.01601(3) 166 165.9302995(22) 0.33503(36) 167 166.9320546(22) 0.22869(9) 168 167.9323767(22) 0.26978(18) 170 169.9354702(26) 0.14910(36) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page