Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 72 Hf 174 173.9400461(28) 0.0016(1) 178.49(2) 176 175.9414076(22) 0.0526(7) 177 176.9432277(20) 0.1860(9) 178 177.9437058(20) 0.2728(7) 179 178.9458232(20) 0.1362(2) 180 179.9465570(20) 0.3508(16) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page