Use of Instrumental Neutron Activation Analysis to investigate the distribution of trace elements among subsamples of solid materials

The results of analytical measurements performed with solid-sampling techniques are affected by the distribution of the analytes within the matrix. The effect becomes significant in the case of determination of trace elements in small subsamples. In this framework we propose a measurement model based on Instrumental Neutron Activation Analysis to determine the relative variability of the amount of an analyte among subsamples of a material. The measurement uncertainty is evaluated and includes the counting statistics, the full-energy gamma peak efficiency and the spatial gradient of the neutron flux at the irradiation position. The data we obtained in a neutron activation experiment and showing the relative variability of As, Au, Ir, Sb and W among subsamples of a highly pure Rh foil are also presented.