Progress in the Determination of the Avogadro Constant
ZHANG Ji-tao1,LUO Zhi-yong2,ZHAO Ke-gong2
1.State Key Lab of Precision Measurement Technology & Instruments, Department of Precision Instruments & Mechanology, Tsinghua University, Beijing 100084, China
2.National Institute of Metrology, Beijing 100013, China
Abstract：The progress in the determination of the Avogadro constant(NA) is reviewed. The x-ray crystal density method is considered as one of the most accurate route to determine NA. According to this method, the molar mass, density and lattice parameter of the single crystal silicon could be measured accurately, then a relative measurement uncertainty 2×10-8 of NA is achievable. The determination of the molar mass, the diameter of the silicon sphere, and the thickness of the oxide layer on the silicon sphere are key issues that affect the measurement accuracy of NA currently,and the focal points for further reseach of the datermination NA is presented.
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2012, Vol. 33 
