Weijun Guo

Preliminary studies on K and L coincidence spectroscopy for optimizing the in vivo XRF measurement of lead in bone

Previous studies treated the optimal combined K and L XRF system which consists of a Cd-109 point source, a low energy Ge detector (LEGe) and a Si(Li) detector. The Monte-Carlo library least-squares (MCLLS) approach and differential operator approach were treated separately. In this work, an approach for combining the MCLLS approach with the differential operator approach (MCDOLLS) is presented and an optimal configuration for coincidence spectroscopy of K and L X-rays is proposed based on preliminary experimental data.

Development of a Monte Carlo—Library Least-Squares code package for the EDXRF inverse problem

The Monte Carlo – Library Least-Squares (MCLLS) approach has now been developed, im plemented, and tested for solving the inverse problem of EDXRF sample analysis. It consists of a linear library least-squares (LLS) code and a comprehensive Monte Carlo code named CEARXRF that is capable of calculating the unknown sample spectrum, all the elemental library spectra in the sample, and the differential operators for each library spectrum with respect to each element. Two codes with Graphical User Interface (GUI) have been designed to implement the MCLLS approach and benchmark results are presented for the two stainless steel samples; SS304 and SS316. The results are accurate, the system is easy to use, and all indications are that this approach will be very useful for the EDXRF practitioner.

A MONTE CARLO CODE FOR SIMULATION OF PULSE PILE-UP SPECTRAL DISTORTION IN PULSE-HEIGHT MEASUREMENT

The Monte Carlo simulation code CEARPPU has been improved to obtain better accuracy for predicting pulse-height spectra measured at high counting rates. Experimental verification was carried out by measuring an Fe-55 spectrum with a Si(Li) X-ray spectrometer. Based on the spectrum measured at low counting rate, which is considered to be the “true” spectrum with no pulse pile-up distortion, the predicted high counting-rate spectrum by CEARPPU is in excellent agreement with the measured one for all of the folded regions due to pulse pile-up. This code is available for public dissemination at Oak Ridge National Laboratory (ORNL) through RSICC. By iteratively using this code, a Monte Carlo approach MCPUT has been proposed and demonstrated for solving the “inverse problem” to make pulse pile-up corrections for pulseheight spectra measured at high counting rates.