Comparison of the aerodynamic size distribution of chain-like aggregates measured with a cascade impactor and a spiral centrifuge.

Several authors have suggested that chain-like aggregates fragment in the jets of cascade impactors and that the impactor consequently underestimates the median aerodynamic diameter and overestimates the geometric standard deviation (GSD). The aerodynamic size distribution of (Pu0.14U0.86)02.2 aggregates were measured simultaneously with two Mercer cascade impactors and a LAPS spiral centrifuge to investigate this problem. Although the median aerodynamic diameters were generally in good agreement, the impactor consistently measured higher values for the GSD than did the spiral centrifuge. Based on experiments in which losses in the centrifuge inlet were measured, it was concluded that the centrifuge had measured the aerodynamic size distribution more accurately than the impactor. Interception of chain-like aggregates on the first few impactor stages may have been the primary reason for the disparity between the impactor and centrifuge measurements.