F01 Use of the Monte Carlo Simulation Code CEARXRF for the EDXRF Inverse Problem

Abstract

The EDXRF inverse problem is solved by first correcting (if necessary) the sample pulseheight spectrum for pulse pile-up with the Monte Carlo code CEARPPU. Then the Monte Carlo - Library Least-Squares (MCLLS) approach is used. This approach consists of using a forward Monte Carlo code (CEARXRF) that is capable of simulating the complete non-linear pulse-height spectral response of any EDXRF system. Using an original estimate of the unknown sample elemental composition, the CEARXRF code is used to simulate the total and individual library spectral responses of all elements. These libraries are then used with the linear Library Least-Squares (LLS) approach to calculate the elemental amounts. Iterations of these steps are made until the estimated and calculated amounts are within prescribed limits so that the measurement non-linearity is accounted for. The two additional features of Differential Operators and all necessary fundamental parameters have been added to the CEARXRF code and a Graphical User Interface (GUI), respectively, that now allows complete automation of this inverse analysis from qualitative to quantitative. The first of these allows iterations without additional Monte Carlo simulation while the second allows initial qualitative as well as quantitative analysis. Benchmark experimental results are given for a series of aluminum alloy samples for a prototype system that employs the radioisotope source 109 Cd and a Si(Li) detector. These results indicate that the approach is accurate and should be very useful to the EDXRF analyst.