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

TL;DR

This study demonstrates a neutron activation analysis method to estimate the 30Si content in highly enriched 28Si, aiming for precise measurements crucial for determining the Avogadro constant.

Contribution

We developed a relative neutron activation analysis technique using a natural silicon standard to estimate 30Si in enriched silicon, achieving an estimated 4% measurement uncertainty.

Findings

Potential to measure 30Si mole fraction with 4% uncertainty

Validated a relative NAA method for ultra-pure silicon

Modeled expected measurement precision based on experimental data

Abstract

We investigated the use of neutron activation to estimate the 30Si mole fraction of the ultra-pure silicon material highly enriched in 28Si 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 modeled experimentally the signal that would be produced by a sample of the 28Si-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 30Si mole fraction of the 28Si-enriched material might reach a 4% relative combined standard uncertainty.