Abstract：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 28Si-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.
［1］Fujii K, Bettin H, Becker P, et al. Realization of the kilogram by the XRCD method［J］. Metrologia, 2016, 53(5): A19-A45.
［2］Becker P. The new kilogram definition based on counting the atoms in a 28Si cystals［J］. Contemporary Physics, 2012, 53(6): 461-479.
［3］Becker P, Pohl H J, Riemann H, et al. Enrichment of silicon for a better kilogram［J］. Physica Status Solidi,2010, 207(1):49-66.
［4］Andreas B, Azuma Y, Bartl G, et al. An accurate determination of the Avogadro constant by counting the atom in a 28Si crystal［J］. Physical Review Letters, 2011, 106: 030801.
［5］Kuramoto N, Azuma Y, Inaba H, et al. Volume measurement of 28Si spheres by an optical interferometer with a flat etalon to determine the Avogadro constant［J］. Metrologia, 2011, 48(2):S83-95.
［6］Azuma Y, Barat P, Bartl G, et al. Improved measurement results for the Avogadro constant using a 28Si-enriched crystal［J］. Metrologia, 2015, 52(2):360-375.
［7］LUO Z Y, GU Y Z, ZHANG J,et al. Interferometric Measurement of the Diameter of a Silicon Sphere With a Mechanical Scanning Method［J］. IEEE Transactions on Instrumentation and Measurement, 2010, 59(11):2991-2996.
［8］LUO Z Y, LI Z H. A new route for length measurement by phase-shifting interferometry［J］.Science China(Physics,Mechanics & Astronomy),2012, 55(4):599-604.
［9］罗志勇. 质量自然基准的研究进展及发展方向［J］. 计量学报, 2004, 25(2): 138-141.
［10］罗志勇, 杨丽峰, 顾英姿, 等. 阿伏加德罗常数测量中单晶硅密度的绝对测量［J］. 计量学报, 2008, 29(3):211-215.
［11］罗志勇. 单晶硅球密度的绝对测量［J］. 计量学报, 2012, 33(5):428-431.
［12］罗志勇, 杨丽峰, 陈允昌. 标准硅球直径精密测量系统的设计［J］. 计量学报, 2005, 26(4): 289-294.
［13］Andreas B, Fujii K, Kuramoto N, et al. The uncertainty of the phase-correction in sphere-diameter measurements［J］. Metrologia, 2012,49:479-486
［14］李岩, 张继涛, 罗志勇.阿伏加德罗常数测量与千克重新定义［J］. 科学通报, 2011, 56(10):717-724.
［15］Davis R, Barat P, Stock M. A brief history of the unit of mass: continuity of successive definitions of the kilogram［J］. Metrologia, 2016, 53(5):A12-A18:
［16］BIPM. 2014 CODATA recommended values［EB］. http://www.bipm.org/en/bipm/mass/avogadro,2017-08-11.
2018, Vol. 39 
