Calibration of the Mars Science Laboratory Alpha Particle X-ray Spectrometer for Analysis of Visible Elements and Light Invisible Components by Glynis Mary Perrett A Thesis Presented to The University of Guelph In partial fulfilment of requirements for the degree of Doctor of Philosophy in Land Resource Science Guelph, Ontario, Canada © Glynis Mary Perrett, April, 2015 ABSTRACT CALIBRATION OF THE MARS SCIENCE LABORATORY ALPHA PARTICLE X-RAY SPECTROMETER FOR ANALYSIS OF VISIBLE ELEMENTS AND LIGHT INVISIBLE COMPONENTS Glynis Mary Perrett Advisors: University of Guelph, 2015 Dr. S. Glasauer Dr. J. L. (Iain) Campbell The Alpha Particle X-ray Spectrometer (APXS) is a small, lightweight instrument capa- ble of detecting geologically significant elements (Na-Y) in a sample through particle induced X-ray emission and X-ray fluorescence. This makes it an ideal instrument for planetary ex- ploration and it has been on every successful NASA rover mission. This thesis covers the fundamental parameters elemental calibration for the newest APXS instrument onboard the Mars Science Laboratory (MSL) rover, Curiosity. This calibration approach assumes all samples are homogeneous at the sub-micron scale, which is incorrect for geologic materi- als, the primary target materials of the APXS. Specific elements in geochemical reference materials were discovered to systematically deviate from certificate values; these “mineral phase effects (MPEs)”, have been quantitatively described for the three lightest detectable elements (Na, Mg, Al), which display the largest deviations. Examination of mineral theo- retical X-ray yields and bulk elemental theoretical X-ray yields of a geochemical reference material (GRM) showed differences that agree in magnitude with the differences observed in the calibration. This verified that the root cause of the MPEs is the necessary homogeneity assumption. To complete the theoretical yield calculations, accurate mineral abundances and elemental composition must be known. Mineral abundances were determined by X-ray diffraction (XRD) and Rietveld analysis. Mineral elemental composition calculations relyon the bulk chemistry and mineral abundances. These calculations are complex, so a program was developed (APXRD) to compute mineral elemental compositions. APXRD was tested against by-hand calculations and the results agree. APXRD may be used in the future to simplify the study of MPEs in more complex GRMs and Martian APXS targets. MPEs have also been studied using the Guelph proton microprobe, which has replicated MPEs observed in select APXS spectra. These analyses show the value of further MPEs studies with the proton microprobe. Calibration of the L훼 scatter peaks method for determining additional light invisible components (ALICs) of MSL APXS targets has been completed. This calibration was tested on GRMs with known ALIC content and it was able to reproduce the known GRM ALIC content where ALICs are greater than 5 oxide wt%. Preliminary analyses of MPE corrections and ALIC content of MSL APXS spectra are presented. Acknowledgements The six years I have dedicated to the completion of my thesis have been both challenging and rewarding. The additional complications of being an interdisciplinary student straddled between two departments were met with amazing support from many individuals in various capacities. For this I am so very grateful. I would like to thank those in both Physics (Reggi Vallille, Steve Kempf, Janice Hall) and SES (Marie Vickary, Linda Bissell) who helped facilitate my unique situation in an administrative context. I am grateful for the excellent work by Steve Wilson in the Physics machine shop. His insightful input for experimental design, and speedy, high-quality work helped smooth experimental procedures. David Atkinson in the Physics chemical laboratory was a great help in the collection of chemical standards, development of laboratory procedures, and general discussions. Steve Sadura in SES provided invaluable geochemical and mineralogical information on numerous occasions. The programming support provided by John Maxwell was crucial to my thesis and I am so thankful for his great work and the time he saved me. Several aspects of my thesis have also benefited from various discussions we have had over the years. Thank you to the APXS crew past, present,at Guelph, and at other institutions. You have been an excellent team to work with and I appreciate all of the insightful conversations I have had with each of you. I particularly appreciate the additional support and guidance provided by Irina Pradler, Stefan Andrushenko, and Chris Heirwegh. I am indebted to my advisory committee for all of the time each member has spent advising me throughout my degree. Ralf Gellert, Penny King, and Mariek Schmidt have provided excellent guidance not only regarding my PhD research, but they have also provided guidance towards improving my skills as a scientist and researcher. My advisors, Susan Glasauer and Iain Campbell, have gone above and beyond to support me throughout my degree. Thank you for taking me on in such a unique, interdepartmental, arrangement, and for going out of your way to make it work. I have learned so much from both Susan and Iain, from physics and geochemistry, to laboratory techniques, diplomacy, and how to write scientifically. I cannot express my gratitude enough. Last but not least, I would like to thank my friends and family. To my friends, thank you for always being there to listen when times were tough and being there to celebrate the big moments. Your constant encouragement has been a source of strength these past six years. Thank you, Dustin, for your excellent cooking, editorial skills, insightful research- based conversations, and never-ending patience. Without your daily support these last few months I can guarantee this process would have been much more challenging. To Mom, Dad, and Braden, thank you for your ceaseless love and support, particularly when I have encountered difficult times. Thank you for pushing me to be the best I can be,especially when I was younger, no matter the circumstances. Without your belief in my ability, I most certainly would not have had the courage or capacity to complete this PhD. iv Contents List of Acronyms xiv 1 Introduction 1 1.1 The Alpha Particle X-ray Spectrometer in Detail . .3 1.2 APXS Spectrum Treatment Methods . .5 1.2.1 Semi-Empirical Method Used on the Mars Exploration Rovers . .6 1.2.2 GUAPX: A Fundamental Parameters Approach to Interpretation of APXS Spectra . .8 2 Elemental Calibration of the Mars Science Laboratory Alpha Particle X- ray Spectrometer by a Fundamental Parameters Approach 12 2.1 Introduction and Overview . 12 2.2 Geochemical Reference Materials . 13 2.3 Sample Preparation . 17 2.4 Instrument Parameters Required for the GUAPX Fitting Program . 21 2.4.1 Defining the Transmissivity (tZ ) of the APXS Window . 21 2.4.2 Effective Angles for the MSL APXS . 22 2.4.3 훼=Lx and H-value Determination . 23 2.4.4 FEU Low Energy Cut Off Correction . 25 2.4.5 Spectrum Calibration in GUAPX . 25 2.5 GUAPX Calibration Procedure . 28 2.6 Element Concentration Offsets in the FEU . 29 2.6.1 Aluminum Offset . 30 2.6.2 Calcium Offset . 31 2.6.3 Titanium Offset . 31 2.6.4 Chromium, Nickel, and Copper Offsets . 31 2.6.5 Yttrium Offset . 31 2.6.6 Phosphorous Offset . 32 2.6.7 Final Remarks . 32 2.7 FEU Calibration Results and Discussion . 33 2.7.1 Major Elements . 34 2.7.2 Minor and Trace Elements . 37 2.7.2.1 Elements Significantly Excited by PIXE: P, S, Cl . 38 2.7.2.2 Ti: Approximately Equal Excitation by PIXE and XRF . 45 2.7.2.3 Elements Excited Predominantly by XRF . 46 2.8 Limits of Detection and Limits of Quantitation . 52 2.9 Errors . 54 v 2.10 Cross Calibration with the PFM . 56 2.11 Summary . 57 3 Mineral Phase Effects 60 3.1 Introduction . 60 3.2 Empirical Correction Factors . 63 3.3 Mineral Phase Effects: Qualitative Description . 64 3.3.1 Aluminum . 65 3.3.2 Sodium . 66 3.3.3 Magnesium . 66 3.4 Mineralogy of GRMs . 68 3.4.1 Detailed Mineralogy of Five Selected GRMs . 70 3.4.1.1 Mineralogy of GA and GH . 73 3.4.1.2 Mineralogy of ISH-G and MDO-G . 73 3.4.1.3 Mineralogy of BCR-2 . 74 3.5 Mineral Phase Effects: Quantitative Determination . 75 3.5.1 APX-Yield . 75 3.5.2 Determining Elemental Compositions of Minerals . 75 3.5.3 Calculating Weighted Mineral Y1 Values . 77 3.5.4 Calculating R(Y1) ............................. 78 3.6 Discussion of Results . 80 3.6.1 Silicon . 80 3.6.2 Aluminum . 80 3.6.3 Sodium . 80 3.6.4 Magnesium . 81 3.6.5 Potassium, Calcium, and Iron in ISH-G and MDO-G . 82 3.6.6 Summary . 83 3.7 PIXE Emulation of the APXS to Test for Mineral Phase Effects . 83 3.7.1 Results for the BT-2 Pressed Pellet . 85 3.7.2 Results for the BT-2 Solid Rock Slab and Thin Section . 86 3.7.3 Summary . 87 3.8 Conclusion . 87 4 APXRD: A Computer Program to Determine Mineral Composition 89 4.1 Introduction . 89 4.2 Details of the APXRD Program . 90 4.3 Comparison of APXRD to By-Hand Results . 92 4.3.1 Mineral Elemental Compositions . 92 4.3.1.1 BCR-2 . 92 4.3.1.2 ISH-G and MDO-G . 94 4.3.1.3 GA and GH . 95 4.3.2 APXRD Derived R(Y1) Values for the Five Test GRMs . 96 4.3.2.1 BCR-2 . 97 4.3.2.2 ISH-G and MDO-G . 99 4.3.2.3 GA and GH . 100 4.3.3 Summary . 101 4.4 New GRM R(Y1) Results and Discussion .