| Isotopic reference materials serve as the “weight” for isotopic measurement,and isotopic compositions of reference materials are basic parameters for isotopic measurement.The preparation and calibration of international isotopic reference materials have already experienced a history of more than 50 years and gone through a tortuous road. Since 1980′s,the preparation and calibration of international isotopic reference materials have entered into a new period of smooth development. Under the guidance and organization of IAEA and associate organization,quite a number of scientists have taken active part in this task,and a series of isotopic reference materials have been established and widely used. Calibration of these isotopic reference materials has been carried out through inter-comparison. Besides,absolute isotope ratios of a number of isotopic reference materials are determined. These achievements can be regarded as great contributions to the unification of datum mark and scale of isotopic measurements. In the meanwhile,re-determination has been made on “Avogadro constant” as well as on atomic weights of a number of elements. |