Abstract: The Determination of Atomic Weights of Antimony,\=Europium,Cerium and ErbiumAuthor Zhao Motian,Wang Jun\=(National Research Center for Certified Reference Material,Beijing 100013,China)\=\=Received 1998-12-30\=\= Abstract \=\;Calibrated mass spectrometric measurements on highly enriched isotopes of Sb,Eu,Ce,Er in the form of oxides of well-defined purity were carried out using a thermal ionization mass spectrometer,yielding absolute isotopic compositions(see table 2)and atomic weights of antimony,europium,cerium and erbium as 121,7597(7)Sb,151,9644(4)Eu,140,1157(8)Ce and 167,2591(9)Er with an uncertainty given on the basis of 95% confidence limit.\=\=Key Words: atomic weight,absolute isotope abundance,antimony,europium,cerium,erbium