On the equivalence between homogeneously prepared sources and sources prepared by seeding in layers for different geometries, energies and matrix parameters.

Measuring the radioactive content of environmental samples requires the use of appropriate reference materials with the same composition and density as the matrices to be measured. If they are not available, ad hoc artificially spiked reference materials are an alternative. Spiking in layers requires a detailed study of the drop distribution, as energy and decay scheme of the component radionuclides must be taken into account to produce a reference material that represents, in efficiency terms, a real sample. A method based on Monte Carlo simulation has been developed to find the optimal distribution of drops in layers for the combination of two typical soil samples and four radionuclides. Results have been validated by comparison with samples prepared by two techniques: methanol bath and spiking in layers.