Neutron activation analysis of the 30Si content of highly enriched 28Si: proof of concept and estimation of the achievable uncertainty

We investigated the use of neutron activation to estimate the Si-30 mole fraction of the ultra-pure silicon material highly enriched in Si-28 for the measurement of the Avogadro constant. Specifically, we developed a relative method based on instrumental neutron activation analysis and using a natural-Si sample as a standard. To evaluate the achievable uncertainty, we irradiated a 6 g sample of a natural-Si material and modelled experimentally the signal that would be produced by a sample of the Si-28-enriched material of similar mass and subjected to the same measurement conditions. The extrapolation of the expected uncertainty from the experimental data indicates that a measurement of the Si-30 mole fraction of the Si-28-enriched material might reach a 4% relative combined standard uncertainty.