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Recent Advances in EDXRF Research CEAR

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Recent Advances in EDXRF Research CEAR

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    1. CEAR Meeting 2006 1 Recent Advances in EDXRF Research @CEAR Weijun Guo, Robin P. Gardner, and Fusheng Li Center for Engineering Applications of Radioisotopes (CEAR) Nuclear Engineering Department North Carolina State University Raleigh, NC 27695-7909 Sep 5, 2006

    2. CEAR Meeting 2006 2 OUTLINE Introduction Spectrum Correction for Pulse Pile-Up Distortion The Monte Carlo – Library Least-Squares (MCLLS) Approach Experimental Results for Alloys Discussion, Conclusions, and Future Work This page for outlineThis page for outline

    3. CEAR Meeting 2006 3 INTRODUCTION EDXRF has always had the two problems of: (1) measuring X-ray intensity and (2) dealing with non-linear response. The present MCLLS approach provides the means for a practical very accurate solution to both of these problems – thus providing a practical very accurate solution to the EDXRF inverse problem. This slide shows the applications of Gamma-source gaugesThis slide shows the applications of Gamma-source gauges

    4. CEAR Meeting 2006 4 SPECTRUM CORRECTION FOR PULSE PILE-UP DISTORTION High counting rates cause pulse pile-up spectral distortion and changes in the statistics. The Monte Carlo code CEARPPU can be used off-line to correct for both of these things. References: 1. R.P. Gardner and S.H. Lee, “Monte Carlo Simulation of Pulse Pile Up”, Denver X-Ray Conference, Advances in X-Ray Analysis [CD ROM], ICDD, Newtown Square, PA, pp. 941-950 (1999). 2. R.P. Gardner, W. Guo, and F. Li, “A Monte Carlo Code for Simulation of Pulse Pile-Up Spectral Distortion in Pulse-Height Measurement”, 53rd Denver X-Ray Conference (2004). 3. Weijun Guo, S.H. Lee, and R.P. Gardner, “The Monte Carlo Approach MCPUT for Correcting Pile-Up Distorted Pulse-Height Spectra”, Nuclear Instruments and Methods A, 531, pp. 520-529 (2004).

    5. CEAR Meeting 2006 5 THE MONTE CARLO – LIBRARY LEAST-SQUARES (MCLLS) APPROACH General Approach The CEARXRF Monte Carlo Code Detector Response Functions Library Least-Squares (LLS) Analysis

    6. CEAR Meeting 2006 6 GENERAL APPROACH 1. The Monte Carlo Code CEARXRF is used with an Elemental Composition Estimate to Generate Elemental Library Spectra and Differential Operators. 2. The Library Least-Squares (LLS) Method is used with the Generated Libraries on the Experimental Spectrum to Obtain the Calculated Elemental Composition. 3. If Calculated and Estimated Spectra are too far Apart Iterate Step 2 by Using Differential Operators to Update the Elemental Libraries. (In rare cases Step 1 is needed.) REFERENCE: Weijun Guo, Robin P. Gardner, and Andrew C. Todd, “Using the Monte Carlo - Library Least-Squares (MCLLS) Approach for the in vivo XRF Measurement of lead in Bone”, Nuclear Instruments and Methods in Physics Research A, 516, pp. 586-593, 2004.

    7. CEAR Meeting 2006 7 GENERAL PROCEDURE of MCLLS

    8. XRFQUAL & XRFQUERY GUI PACKAGE XRFQual + XRayQuery XRFQual: Qualitative analysis of XRF measured spectrum Energy Calibration Composition Identification XRayQuery Interactive tool for X-ray physics, such as characteristic x-ray line energy, yield, etc.

    9. CEAR Meeting 2006 9 THE CEARXRF MONTE CARLO CODE (CEARXRF) A Specific Purpose Monte Carlo Code under Development since before 1975 - first benchmarked with the Sherman Equations (in that process two typos were found in the Sherman tertiary equations). Variance Reduction Methods include Use of Detector Response Functions (DRF’s) for Si(Li) detector and GE Detector. All the pertinent physics has been added over the years including differential operators and a complete geometry treatment. The code has been extensively benchmarked.

    10. CEAR Meeting 2006 10 MAIN FEATURES OF CEARXRF CEARXRF is a specific purpose Monte Carlo code for modeling the complete spectral response of energy-dispersive X-ray fluorescence (EDXRF) spectrometers, developed by CEAR since 1977. Current Version is 4. The CEARXRF code has man features that make it suitable for a variety of applications. They include: (1) multiple-element EDXRF simulation (Z=1-94), (2) complete EDXRF pulse-height spectrum calculation, (3) a variety of excitation modes, (4) polarized photon transport modeling, (5) complete K and L XRF simulation, (6) detailed XRF emission physics, (7) Doppler effect modeling in Compton scattering, (8) general geometry modeling, (9) spectroscopy analysis with the MCLLS approach, (10) correlated sampling for density and composition perturbation calculation, (11) detector response function Si(Li) and low-energy photon germanium detectors, (12) phton cross sections adapted from MCNP (Briesmeister, 1997) and latest atomic data, (13) optimized variance reduction techniques for EDXRF modeling, (14) differential operator technique, and (15) graphical interface to display simulation results on the fly, (16) Coincidence spectra

    11. CEARXRF DEVELOPMENT-FUTURE VERSION 5 Rewrite the program by Fortran 90/95, upgraded from Fortran 77. Geometry part of CEARXRF will be compatible with MCNP5 and users can use VisEdt to view and modify the input file. Update the cross section library in CEARXRF with newest data available. And ENDF/B6 libraries will be used directly to make it easier for future updates. Coincidence part of CEARXRF will be updated based on previous work. XFCT(X-Ray Fluorescence Computed Tomography) simulation application by CEARXRF

    12. CEAR Meeting 2006 12 DETECTOR RESPONSE FUNCTIONS Detector Response Functions (DRF’s), R(E,E), are pdf’s that give the pulse-height distribution E as a function of the incident energy E. DRF’s are very effective variance reduction methods. They can be obtained by semi-empirical or Monte Carlo approaches that use approximations. They provide the accuracy required for the MCLLS approach.

    13. SIMULATED FLUX & SPECTRUM AFTER DRF – GE DETECTOR

    14. MONTE CARLO LIBRARY SPECTRA(AFTER DRF) –GE DETECTOR

    15. CEAR Meeting 2006 15 ILLUSTRATION OF FLUX POINTS AFTER DRF –Si(Li) DETECTOR

    16. CEAR Meeting 2006 16 LIBRARY SPECTRA (AFTER DRF) & BACKGROUND NOISE – SI(LI) DETECTOR

    17. CEAR Meeting 2006 17 LIBRARY LEAST-SQUARES ANALYSIS The Library Least-Squares (LLS) approach was originally derived and used by Salmon1 in 1961 for gamma rays from radioisotopes. It is the most fundamental approach to the inverse spectral analysis problem, it uses all the spectral data and gives the best accuracy, and it automatically provides estimates of goodness of fit and statistics. 1Salmon, L., 1961, “Analysis of Gamma-Ray Scintillation Spectra by the Method of Least Squares”, Nuclear Instruments and Methods, 14, pp. 193-199.

    18. DIFFERENTIAL OPERATOR (DOLLS) If the fitted results from MCLLS are far from the previous results, a new run is required. Simulation based on a “better guess” is performed. CEARXRF can be executed again. But it is very time consuming (maybe 3-4 hours to run 1E8 histories) compared to Differential Operator, which provides a faster and also accurate way (3-10minues).

    19. CEAR Meeting 2006 19 EXPERIMENTAL ARRANGEMENT

    20. CEAR Meeting 2006 20 EXPERIMENTAL RESULTS FOR ALLOYS Stainless Steel (SS304) - excited by Cd-109 Aluminum Alloys (AA7178 & AA3004)– Standards provided by Alcoa for some research on thickness gauges – excited by Cd-109 and Fe -55.

    21. CEAR Meeting 2006 21 STAINLESS STEEL 304 (SS304) QUALITATIVE ANALYSIS

    22. CEAR Meeting 2006 22 STAINLESS STEEL 304 (SS304) EXPERIMENTAL & FITTED DATA

    23. CEAR Meeting 2006 23 TABLE 1. SS304 FIT RESULTS

    24. CEAR Meeting 2006 24 ALUMINUM ALLOY 7178 (AA7178) EXPERIMENTAL AND FIT SPECTRA

    25. CEAR Meeting 2006 25 TABLE 2. AA7178 FIT RESULTS

    26. CEAR Meeting 2006 26 ALUMINUM ALLOY 3004 (AA3004) EXPERIMENTAL & FIT SPECTRA

    27. CEAR Meeting 2006 27 TABLE 3. AA3004 FIT RESULTS

    28. CEAR Meeting 2006 28 Fe-55 EXCITATION OF Al

    29. CEAR Meeting 2006 29 DISCUSSION, CONCLUSIONS, AND FUTURE WORK - PM Results indicate the approach is accurate. The CEARXRF code and a DRF for the detector provide all that is needed for the inverse problem. The GUI that has been developed and Differential Operators added to CEARXRF makes the approach practical. Now we need to develop the approach for all commercial analyzers – including those with X-Ray machines and Secondary fluorescers.

    30. CEAR Meeting 2006 30 DISCUSSION, CONCLUSIONS, AND FUTURE WORK - AM For Routine XRF Sample Analysis the Advantages of this Approach are: Use of CEARPPU makes all the data available with known Poisson statistics. Use of MCLLS corrects for all matrix effects including tertiary and beyond. It will be easy to include other refinements as necessary. Use of LLS avoids all problems with intensity measurement and gives statistical estimates of results automatically. An error analysis of existing FP approaches will be made.

    31. CEAR Meeting 2006 31 ACKNOWLEDGEMENT The authors acknowledge two grants by the National Institute of Environmental Health of the NIH for providing the opportunity for optimizing the XRF approaches for the in vivo measurement of lead in bone.

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