LASER INDUCED BREAKDOWN SPECTROSCOPY: INVESTIGATION OF LINE PROFILES, SLURRIES AND ARTIFICAL NEURAL NETWORK PREDICTION By Seong Yong Oh A Dissertation Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Engineering with an Emphasis in Applied Physics in the Department of Physics and Astronomy Mississippi State, Mississippi December 2007 Copyright by Seong Yong Oh 2007 LASER INDUCED BREAKDOWN SPECTROSCOPY: INVESTIGATION OF LINE PROFILES, SLURRIES AND ARTIFICAL NEURAL NETWORK PREDICTION By Seong Yong Oh Approved: _________________________________ _________________________________ Jagdish P. Singh David L. Monts Adjunct Professor of Physics and Professor and Graduate Coordinator of Research Professor of Institute for Clean Physics Energy Technology (Co-Major Professor) (Director of Dissertation and Major Professor) _________________________________ _________________________________ Fang Yu Yueh Chun Fu Su Research Scientist II of Institute for Clean Professor of Physics Energy Technology (Committee Member) (Committee Member) _________________________________ _________________________________ Thomas Philip Chuji Wang Professor of Computer Science and Assistant Professor of Physics Engineering (Committee Member) (Committee Member) ________________________________ W. Glenn Steele, Jr. Interim Dean of the Bagley College of Engineering Name: Seong Yong Oh Date of Degree: December 14, 2007 Institution: Mississippi State University Major Field: Applied Physics Major Professor: Dr. Jagdish P. Singh Title of Study: LASER INDUCED BREAKDOWN SPECTROSCOPY: INVESTIGATION OF LINE PROFILES, SLURRIES AND ARTIFICAL NEURAL NETWORK PREDICTION Pages in Study: 129 Candidate for Degree of Doctor of Philosophy Laser induced breakdown spectroscopy (LIBS) was tested to examine its applicability to remote and in suit analysis in inaccessible situation. Two types of liquid sample (slurry) prepared for simulating vitrification of liquid hazardous wastes was tested. In situ analysis ability makes the LIBS technique practical for analysis of the slurry samples during vitrification, which is in inaccessible situation. For the first slurry sample, two slurry circulation systems were devised to overcome major technical problems associated with LIBS measurements of slurry samples - namely sedimentation and change in the lens-to-sample distance (L.T.S.D) during measurement. The second slurry sample contained less water and is able to be managed in a small glass container during test. We applied direct analysis of slurry sample filled in glass container. Spectroscopic analysis was performed using two different detection systems: Czerny-Turner and Echelle spectrometer systems. In particular, spectroscopic analysis of data from an echelle spectrometer shows the high efficiency for simultaneously determining physical quantities of all elements of interest. We also evaluate LIBS technique to tin alloy samples for the purpose of quantitative analysis by using Echelle spectrometer system. Unknown samples without information of elemental composition were tested to estimate several sample compositions simultaneously. An artificial neural network, calibration method, and chemical analysis were applied to estimate the elemental concentrations of impurities in tin (Sn) alloy. Key words: Slurry, Laser induced breakdown spectroscopy, Line profile ACKNOWLEDGMENTS I would like to thank Dr. Kuntz, Dr. Monts and my advisor professor Dr. Singh. Theoretical part of my thesis is based on a paper written by Dr. Kuntz. When I had trouble in finding the error of computer coding about the Voigt line profile, Dr. Kuntz sent me his FORTRAN coding. With the help of his coding, I found the error and completed the coding. Dr. Monts gave me good correction and desirable direction of my writing. In particular, Dr. Monts’s direction is like lamp in dark for my writing. I really appreciate my advisor, Dr. Singh for hiring me as a graduate student. I would like to thanks Institute for Clean Energy Technology (ICET) for providing the financial assistance. ii TABLE OF CONTENTS ACKNOWLEDGMENTS ........................................................................................... ii LIST OF TABLES....................................................................................................... vi LIST OF FIGURES ..................................................................................................... viii CHAPTER I. INTRODUCTION ........................................................................................... 1 1.1 LIBS Advantages and Disadvantages.................................................. 4 1.2 Analysis of Liquid Sample................................................................... 5 1.3 The Objective of This Dissertation...................................................... 6 II. PHYSICS OF LIBS LINE SHAPE & ARTIFICIAL NEURAL NETWORKS........................................................................................ 7 2.1 Plasma Formation by Laser Pulse........................................................ 7 2.2 Spectral Line Intensity ......................................................................... 9 2.3 Local Thermodynamic Equilibrium..................................................... 10 2.4 Voigt Profile......................................................................................... 11 2.5 Relation between Lorentz and Gaussian half width ............................ 16 2.6 Stark Profile for Isolated Neutral Atom Lines..................................... 21 2.7 Line Broadening Width........................................................................ 26 2.7.1 Doppler Broadening Width...................................................... 26 2.7.2 Stark Broadening Width .......................................................... 27 2.8 Self-Absorption.................................................................................... 28 2.9 Curve of Growth .................................................................................. 30 2.10 Spectral Line Intensity in Optical Thin Plasma ................................... 35 2.11 Partition Function and Plasma Temperature........................................ 36 2.12 Artificial Neural Networks .................................................................. 40 2.12.1 Back-Propagation Learning Model.......................................... 40 2.12.2 Cascade-Correlation Learning Model...................................... 43 2.12.3 Software and Data Analysis..................................................... 44 III. EXPERIMENTAL........................................................................................... 45 3.1 Spectrometers....................................................................................... 47 3.1.1 Czerny-Turner Spectrometer System....................................... 47 iii 3.1.2 Echelle Spectrometer System .................................................. 53 IV. LIBS APPLICATION TO IN SITU ANALYSIS OF SLURRY SAMPLES PREPARED FOR THE PURPOSE OF SIMULATING THE VITRIFICATION PROCESS OF LIQUID RADIOACTIVE WASTES.............................................................................................. 64 4.1 Experimental Description .................................................................... 64 4.2 Results and Discussion ........................................................................ 65 4.2.1 Sample Preparation .................................................................. 65 4.2.2 Spectroscopic Comparison....................................................... 66 4.3 Result Recorded by Czerny-Turner Spectrometer System .................. 67 4.3.1 Reproducibility of Line Emission Intensity............................. 67 4.3.2 Laser Power Effect and Calibration Curve of Normalized Intensity.................................................................................... 69 4.4 Result Recorded by Echelle Spectrometer System.............................. 72 4.4.1 Electron Density....................................................................... 72 4.4.2 Plasma Temperature................................................................. 73 4.4.3 Calibration Curve..................................................................... 76 4.5 Conclusion ........................................................................................... 79 V. COMPARATIVE STUDY OF LASER INDUCED BREAKDOWN SPECTROSCOPY MEASUREMENT USING TWO SLURRY CIRCULATION SYSTEMS................................................................ 80 5.1 Experimental Description .................................................................... 80 5.2 Slurry Handling System....................................................................... 82 5.3 Results and Discussions....................................................................... 84 5.3.1 Effect of Laser Pulse Rate........................................................ 84 5.3.2 Slurry Circulation Systems ...................................................... 87 5.3.3 Calibration................................................................................ 91 5.4 Conclusion ........................................................................................... 93 VI. TIN ALLOY ANALYSIS COMBINED WITH ARTIFICIAL NEURAL NETWORK PREDICTION ................................................................. 94 6.1 Experimental Description ...................................................................