  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.
