阿伏加德罗常数测量与千克重新定义

阿伏加德罗常数(N_A)是一个联系微观尺度和宏观尺度的基本物理常数, 它的精确测量可用于重新定义国际基本单位千克和摩尔, 因而有助于推动国际单位制的发展. 现代N_A 测量方法为X 射线晶体密度法, 它以单晶硅为材料, 通过测量其摩尔质量、宏观密度和晶格常量得到N_A, 该方法涉及到的关键技术包括单晶硅材料的生长、大尺寸单晶硅球加工、硅原子量测量技术、X 射线干涉术、精密光学干涉技术、超薄膜厚度及成份测量技术等. 本文综述了现代N_A 测量的研究进展、研究难点和未来的研究方向, 并以千克重新定义为例, 分析了N_A 测量研究在基础计量学领域的重要作用.

Determination of the Avogadro constant and the redefinition of the kilogram

Avogadro constant (N_A) is a fundamental physical constant which constructs the relationship between the microscopic and macroscopic world. The accurate determination of N_A can be used for redefining the base units, e.g. kilogram and mole, so that can promote the development of the International System of Units. An effective route to determine N_A directly is the modern X-ray crystal density method, in which several parameters of the single crystal silicon, such as molar mass, density and lattice parameter should be measured accurately. The key technologies related to this method includes: the growth of highly pure silicon crystals, the manufacture of the silicon sphere, determination of the atomic mass of the silicon isotopes, X-ray interferometry, precision optical interferometry, and the determination of the thickness as well as the chemical composition of the ultra-thin film. The recent progress and potential direction in future of this research is reviewed in this paper. The significance of N_A in the fundamental metrology is also demonstrated by the case of the kilogram redefinition.