Elemental characterization of the Avogadro silicon crystal WASO 04 by neutron activation analysis

Impurity measurements of the 28Si crystal used for the determination of the Avogadro constant are essential to prevent biased results or underestimated ncertainties. A review of the existing data confirmed the high purity of silicon with respect to a large number of elements. In order to obtain direct evidence of purity, we developed a relative analytical method based on neutron activation. As a preliminary test, this method was applied to a sample of the Avogadro natural silicon crystal WASO 04. The investigation concerned 29 elements. The mass fraction of Au was quantified to be (1.03 ± 0.18) × 10−12. For the remaining 28 elements, the mass fractions were below the detection limits, which ranged between 1 × 10−12 and 1 × 10−5.