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

TL;DR

This study developed a neutron activation analysis method to directly assess the purity of the Avogadro silicon crystal WASO 04, confirming its high purity with very low impurity levels.

Contribution

A new relative neutron activation method was applied to evaluate the elemental purity of the Avogadro silicon crystal, providing direct evidence of its high purity and low impurity levels.

Findings

Gold mass fraction quantified at 1.03(18) x 10^-12

Impurities in 28 elements below detection limits

Detection limits ranged from 1 x 10^-12 to 1 x 10^-5

Abstract

Analytical measurements of the 28Si crystal used for the determination of the Avogadro constant are essential to prevent biased results or under-estimated uncertainties. A review of the existing data confirms the high-purity of silicon with respect to a large number of elements. In order to obtain a 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 crystal WASO 04. The investigation concerned twenty-nine elements. The mass fraction of Au was quantified to be 1.03(18) x 10-12. For the remaining twenty-eight elements, the mass fractions are below the detection limits, which range between 1 x 10-12 and 1 x 10-5.