阿伏加德罗常数测量与千克重新定义

Avogadro Constant Determination and Kilogram Redefinition

当千克用固定普朗克常数h的方法定义时,X射线晶体密度法(XRCD)即被用来定义和复现千克,它采用对浓缩28Si原子计数的方法来测量阿伏加德罗常数NA,已将NA和h的测量不确定度达到2×10-8,并反过来确定硅球的质量实现对千克的量值复现。阐述了晶格常数、同位素、浓缩硅、硅球直径及表面氧化层等阿伏加德罗常数测量的关键技术的研究进展。介绍了原子计数法千克定义及其量值复现方法,该方法将为国际单位制改制之后我国质量量值复现提供参考。

When the kilogram is redefined in terms of the fixed numerical value of the Planck constant h, the X-ray crystal density （XRCD） method, among others, is used for realizing the redefined kilogram. The XRCD method has been used for the determination of the Avogadro constant NA by counting the number of atoms in a 2SSi-enriched crystal, contributing to a substantial reduction of uncertainty in the values of NA and h to 2 × 10^-8. This method can be therefore used reversely for the mass determination of a 1 kg sphere prepared from the crystal. The key technologies of lattice constant, isotope, concentration of silicon, diameter of silicon sphere and surface oxide layer are described. The definition of atomic counting method and the method of its value reproduction are introduced. The method will be an important reference for the quality value reproduction of China after the reform of the international system of units.