The influence of particle size is a well-documented source of error in X-ray fluorescence analysis. Changes in particle size alter the effective fluorescence volume of a target element and can therefore produce large shifts in measured fluorescence intensity. These changes in intensity then result in a reduction of quantification accuracy. Conventional fundamental parameter (FP) approaches successfully account for matrix effects- caused by changes in the material’s composition- however they do assume that the material has been prepared so that particle size effects are eliminated.
The particle size effect depends strongly on excitation energy, suggesting that measurements acquired under multiple excitation energies may provide insight into the particle size of the fluorescing material. In this work, a dual-energy excitation methodology is investigated and used to quantify and correct for particle size effects in two sets of samples: synthetic slurry samples, containing copper particles with a range of different particle sizes, and copper feed slurry samples. XRF measurements were performed on both sets of samples, using multiple excitation energies, to characterize changes in the copper fluorescence associated with particle size, independent of composition.
The measured copper fluorescence intensities showed a strong particle size dependence, with the larger copper particles emitting up to 7 times less fluorescence X-rays than smaller particles. Ratios of fluorescence intensity acquired under two excitation conditions showed were used to derive correction factors for these differences. Application of the correction significantly improved agreement between measurements collected from samples with differing particle size distributions.
These results demonstrate that this dual-energy correction method is feasible for characterising particle size effects in XRF analysis. Ongoing work is focused on incorporating these corrections directly into an in-house fundamental parameters analysis software, to create a framework for simultaneous correction of matrix and particle size effects. Such developments have applications in laboratory, handheld, and on-line XRF measurements.