Focused‐beam X‐ray fluorescence and diffraction microtomographies for mineralogical and chemical characterization of unsectioned extraterrestrial samples
Year: 2024
Type: article
Abstract: This study describes the application of new synchrotron X‐ray fluorescence (XRF) and diffraction (XRD) microtomographies for the 3‐D visualization of chemical and mineralogical variations in unsectioned extraterrestrial samples. These improved methods have been applied to three compositionally diverse chondritic meteorite samples that were between 300 and 400 μm in diameter, including samples prepared from fragments of the CR2 chondrite LaPaz Icefield (LAP) 02342, H5 chondrite MacAlpine Hills (MAC) 88203, and the CM2 chondrite Murchison. The synchrotron‐based XRF and XRD tomographies used are focused‐beam techniques that measure the intensities of fluorescent and diffracted X‐rays in a sample simultaneously during irradiation by a high‐energy microfocused incident X‐ray beam. Measured sinograms of the emitted and diffracted intensities were then tomographically reconstructed to generate 2‐D slices of XRF and XRD intensity through the sample, with reconstructed pixel resolution of 1–2 μm, defined by the resolution of the focused incident X‐ray beam. For sample LAP 02342, primary mineral phases that were visualized in reconstructed slices using these techniques included isolated grains of α‐Fe, orthopyroxene, and olivine. For our sample of MAC 88203, XRF/XRD tomography allowed visualization of forsteritic olivine as a primary mineral phase, a vitrified fusion crust at the sample surface, identification of localized Cr‐rich spinels at spatial resolutions of several micrometers, and imaging of a plagioclase‐rich glassy matrix. In the sample of Murchison, major identifiable phases include clinoenstatite‐ and olivine‐rich chondrules, variable serpentine matrix minerals and small Cr‐rich spinels. Most notable in the tomographic analysis of Murchison is the ability to quantitatively distinguish and visualize the complex mixture of serpentine‐group minerals and associated tochilinite–cronstedtite intergrowths. These methods provide new opportunities for spatially resolved characterization of sample texture, mineralogy, crystal structure, and chemical state in unsectioned samples. This provides researchers an ability to characterize such samples internally with minimal disruption of sample micro‐structures and chemistry, possibly without the need for sample extraction from some types of sampling and capture media.
DOI: 10.1111/maps.14130
Language: English
Subfield: Radiation
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,240
Awards: G102163711, G107546177, G1313983767, G1664757510, G2287611682, G2568637690, G262962599, G3075337988, Facility Support: GeoSoilEnviroCARS: A National Resource for Earth, Planetary, Soil and Environmental Science Research at the APS, G498139845, G513797252, G6352361788, G6848031779, G6918803902, THE OXIDATION STATE AND MINERALOGY OF EXTRATERRESTRIAL MATERIALS ARE CRUCIAL PROPERTIES FOR CONSTRAINING THE CONDITIONS UNDER WHICH PRIMITIVE SOLAR SYSTEM OBJECTS ORIGINATED AND EVOLVED. SYNCHROTRON-BASED X-RAY ABSORPTION FINE STRUCTURE (XAFS) TECHNIQUES HAVE PROVEN TO BE VALUABLE IN DEFINING OXIDATION STATE WHERE THE VALENCES OF MULTIVALENT ELEMENTS (TI V CR AND FE) ARE USED AS PROXIES. COUPLED WITH HIGH-SPEED SYNCHROTRON X-RAY MICRODIFFRACTION (MICRO-XRD) MAPPING NEW OPPORTUNITIES ARE AVAILABLE TO CORRELATE CHEMICAL STATE AND MINERALOGY (INCLUDING ORIENTATION AND STRAIN) AT MICROMETER SCALES. THESE METHODS HAVE BEEN APPLIED TO RELATIVELY LARGE (>TENS OF M) MINERAL GRAINS AND GLASSES IN THIN SECTIONS. HOWEVER SAMPLES RETURNED BY NASA SPACECRAFT ARE TYPICALLY CHARACTERIZED BY MINERAL GRAINS OF MUCH SMALLER DIMENSIONS (<10 M). THE PROPOSED WORK WILL DEVELOP AND TEST TECHNIQUES FOR APPLYING MICRO-XAFS AND MICRO XRD METHODS TO PICOGRAM MINERAL GRAINS FOCUSING ON FIB METHODS FOR PRODUCING MONO-MINERALIC SAMPLES. TOMOGRAPHIC TECHNIQUES WILL BE DEVELOPED TO ALLOW THE MINERALOGIC INFORMATION TO BE VISUALIZED IN 3D PROVIDING THE SPATIAL DISTRIBUTION OF A SELECTED CRYSTALLINE OR AMORPHOUS PHASE INSIDE THESE ISOLATED PICOGRAM SAMPLES IDEALLY WITHIN SEALED CONTAINERS AND CAPTURE MEDIA WITHOUT THE NEED FOR EXTRACTION. THE METHODS WILL BE APPLIED TO STARDUST GRAINS FROM COMET WILD-2 AND HAYABUSA1 GRAINS FROM ASTEROID ITOKAWA AND WILL BE APPLICABLE TO RETURNED REGOLITH SAMPLES FROM THE HAYABUSA-2 AND OSIRIS-REX MISSIONS. WE WILL DEVELOP AND TEST MICRO-XAFS AND XRD TECHNIQUES APPLICABLE TO PICOGRAM EXTRATERRESTRIAL SAMPLES USING THE GSECARS X-RAY MICROPROBE AT THE ADVANCED PHOTON SOURCE. FOR FOCUS OF MICRO-XAFS STUDIES WILL BE USING FIB METHODS TO PRODUCE MONOMINERALIC SAMPLES. DEVELOPMENT WILL BE ACCOMPLISHED USING VALENCE STATE STANDARDS (BOTH MINERALS AND GLASSES). FIB SECTIONS WILL ALSO BE MADE OF LARGER MINERAL GRAINS FROM METEORITIC THIN SECTIONS WHERE XAFS SPECTRA FOR THE FIB SAMPLE AND PARENT GRAIN IN THIN SECTION CAN BE USED TO TEST FOR VALENCE ALTERATIONS DUE TO SAMPLE PREPARATION. MICRO-XRD STUDIES WILL ALSO UTILIZE THESE FIB SECTIONS BUT THE ULTIMATE GOAL WILL BE TO DEVELOP METHODOLOGIES FOR SAMPLES THAT ARE MINERALOGICALLY HETEROGENEOUS AT THE MICROMETER SCALE. A NEW GENERATION OF HIGH SPEED AREA DETECTORS WILL BE USED TO COLLECT THE DIFFRACTION DATA IN MAPPING MODE WITH ACCUMULATION TIMES<100 MSEC PER PIXEL. INTERPRETABLE DIFFRACTION PATTERNS WILL BE COLLECTABLE FROM PICOGRAM SAMPLES/VOXELS. WE WILL DEVELOP METHODS TO COLLECT THE DATA TOMOGRAPHICALLY AND RECONSTRUCTION ALGORITHMS TO VISUALIZE THE DIFFRACTION PATTERN WITHIN RECONSTRUCTED SLICES OF THE ANALYZED MATERIALS. THESE METHODS WILL THEN BE APPLIED TO STARDUST MINERAL GRAINS NOTABLY FROM OLIVINE- AND PYROXENE-BEARING TRACKS. THE COUPLED XAFS/XRD DATA MAY ALSO BE USEFUL IN IDENTIFYING MATERIALS PRODUCED/MODIFIED DURING CAPTURE. THIS WORK WILL DEVELOP COORDINATED VALENCE/OXIDATION STATE AND MINERAL PHASE DETERMINATION METHODS APPLICABLE TO PICOGRAM SAMPLES RETURNED BY NASA MISSIONS AND WILL PROVIDE INSIGHTS INTO THE ORIGINS OF SAMPLED SOLAR SYSTEM BODIES. THE RESULTS WILL ALSO LIKELY PROVIDE INSIGHTS INTO THE REDOX EFFECTS AND MINERAL MODIFICATIONS OF SECONDARY PROCESSES SUCH AS RE-MELTING SHOCK AND CAPTURE. THUS THIS STUDY IS RELEVANT TO THE CALL OF THE LABORATORY ANALYSIS OF RETURNED SAMPLES (LARS) PROGRAM ELEMENT., G8277695435, G969889393, G993149817
OpenAlex ID: W4390947493