EVALUATION OF PATH-LENGTH ESTIMATORS FOR CHARACTERIZING MULTIPHASE SYSTEMS USING POLYENERGETIC X-RAY ABSORPTIOMETRY

Abstract

Polyenergetic, high-photon-flux X-ray absorption methods promise to make possible rapid, high-resolution measurements of phase fractions in multiphase systems. Improved statistical methods for data analysis, however, are needed. We develop a set of three new path-length estimators as alternatives to the traditional lumped-energy approach, and we compared this set of estimators for two classes of examples. The experimental comparisons were performed with clean systems to allow reliable measures of accuracy and precision of all material estimates; however, soil systems, for which X-ray attenuation methods have been routinely applied, have radiation attenuation properties similar to the systems used in this work, making these results directly applicable to soil systems. Results show that the new estimators provide more accurate and precise estimates of path length than the traditional lumped-energy approach, especially for challenging, multiple material estimation problems. The bias of estimated path lengths was reduced by at least 80% in all cases and was typically around 90% compared with the standard approach. Our sample results also demonstrate the reliable simultaneous measurement of three material path lengths, a new and desirable capability for multiphase flow experiments. Alternatively, the improved estimators developed in this work can be used to reduce measurement times compared with traditional methods for estimates of similar quality.