30Si Mole Fraction of a Silicon Material Highly Enriched in 28Si Determined by Instrumental Neutron Activation Analysis

TL;DR

This paper presents an independent measurement of the 30Si mole fraction in highly enriched silicon using instrumental neutron activation analysis, supporting the precise isotopic characterization needed for redefining the kilogram.

Contribution

It introduces a neutron activation analysis method to determine 30Si mole fraction, providing an alternative to isotope dilution mass spectrometry.

Findings

Measured 30Si mole fraction consistent with existing standards

Demonstrated the effectiveness of neutron activation analysis for isotopic measurement

Supported the accuracy of isotopic composition used in Avogadro constant determination

Abstract

The latest determination of the Avogadro constant, carried out by counting the atoms in a pure silicon crystal highly enriched in 28Si, reached the target 2x10-8 relative uncertainty required for the redefinition of the kilogram based on the Planck constant. The knowledge of the isotopic composition of the enriched silicon material is central; it is measured by isotope dilution mass spectrometry. In this work, an independent estimate of the 30Si mole fraction was obtained by applying a relative measurement protocol based on Instrumental Neutron Activation Analysis. The amount of 30Si isotope was determined by counting the 1266.1 keV gamma-photons emitted during the radioactive decay of the radioisotope 31Si produced via the neutron capture reaction 30Si(n,gamma)31Si. The x(30Si) = 1.043(19)x10-6 mol mol-1 is consistent with the value currently adopted by the International Avogadro Coordination.