• Crystal Chemistry of Martian Minerals

      Downs, Robert T.; Morrison, Shaunna M.; Downs, Robert T.; Hazen, Robert M.; Prewitt, Charles T.; Denton, M. Bonner; Ducea, Mihai (The University of Arizona., 2017)
      The NASA Mars Science Laboratory (MSL) rover, Curiosity, began exploring Gale crater, Mars in August, 2012 with the primary goal of assessing the past and present habitability of the martian surface. To meet this goal, Curiosity is equipped with an advanced suite of scientific instruments capable of investigating the geology, geochemistry, and atmospheric conditions on Mars. Among these instruments is the CheMin (Chemistry and Mineralogy) X-ray diffractometer whose function is to identify mineral phases present in sediments and rocks by means of X-ray diffraction (XRD). Characterizing the mineralogical make-up of a rock unit is an important step in determining its geologic history. Primary igneous minerals, such as feldspar, olivine, and pyroxene, give information about parental magmas - their composition, temperature, depth and so on. Secondary alteration minerals, like jarosite or akaganeite, point to distinct weathering or diagenetic processes. As such, understanding the mineral occurrence and abundance in Gale crater provides the MSL team with a robust foundation from which to make geologic interpretations. This dissertation details the methods used to determine the chemical composition of selected mineral phases based solely on XRD patterns from CheMin. Curiosity is equipped with instruments capable of measuring bulk composition of a sample [e.g., APXS (Alpha Particle X-ray Spectrometer)] but has no instrument capable of measuring the composition of a single phase in a multi-phase sample. Therefore, we developed crystal chemical algorithms and calibrations based on refined unit-cell parameters in order to predict mineral phase compositions. We have calculated algorithms for plagioclase, alkali feldspar, Mg-Fe-Ca clinopyroxene, Mg-Fe orthopyroxene, Mg-Fe olivine, Fe-oxide spinel, and alunite-jarosite group minerals. Furthermore, we use the estimated compositions of crystalline material in conjunction with bulk sample chemistry from APXS to estimate of the composition of the X-ray amorphous material present in each of the samples analyzed by CheMin in Gale crater.
    • Scatter Based Novel Imaging Systems

      Ashok, Amit; Yang, Shu; Peng, Leilei; Pau, Stanley K.H. (The University of Arizona., 2022)
      Imaging is the process of reproduction of an object’s form. Image science is a multidisciplinary field concerned with the generation, collection, duplication, analysis, modification, and visualization of images.Traditionally, the image of an object is generated by gathering optical power reflected or absorbed by the object directly with a detector array in a one-to-one manner. For example, in optical photography, reflected or emitted photons from object are directly captured by optical elements (e.g. lens, mirror) and focused onto a detector array. However, in many scenarios where such direct imaging is not feasible, one is forced to gather information that is only indirectly related to the object. In some extreme cases, we are forced to work with only scattered photons from the object of interest. In this work, we explore two of these special cases and propose two novel indirect imaging (scattering-based) approaches operating at different wavelengths. The first indirect imaging approach we consider a novel non-line-of-sight (NLOS) imaging technique. Non-line-of-sight imaging refers to the imaging of an object that is not directly visible from the viewer/imaging perspective. A classic NLOS setup usually involves emission and collection of photons actively with time-of-flight measurements. To accurately measure a photon’s traveling time, most approaches employ expensive and exotic optical sources and detectors such as ultrafast laser and ultra high-resolution single photon avalanche detector (SPAD). In this work, we instead propose a novel passive NLOS imaging method that works with ambient light illumination and employs only commonly available imaging elements. We develop a light path order based image formation model, a learning-based model parameter estimation process, and successfully demonstrate instant passive NLOS imaging. We discussed the limitation of this technique and possible applications We then shift our focus to ultra-short wavelength or higher photon energy. In this part, we study a different type of imaging referred to as X-ray diffraction tomography (XRDT). X-ray diffraction tomography is a tomographic imaging of the coherent scattering profile (X-ray form factor) of an object and its material. Coherent scattering is one of three forms of photon interactions possible in the X-ray photon energy ranging from 10 kev to 200 kev. It occurs when X-ray photon energy is relatively small compared to the ionization energy of the atom. When a coherent scattering event happens, the photon does not have enough energy to liberate the electron from its bound state and no energy transfer occurs. Instead, the X-ray photon gains momentum from the micro-structure of the material and undergoes a change in its direction (scatter). Therefore, the scatter direction contains vital information of the micro-structure of the material and is unique to different materials. The scattering pattern is called momentum transfer function or X-ray form factor. It is considered as the golden standard in material classification. In this work, we explore the inherent sparsity in the X-ray form factors and develop a sparsity regularized reconstruction algorithm to perform maximum-a-posteriori estimation for X-ray diffraction tomography. We demonstrate the possibility of achieving higher energy resolution with limited number of photon, which allows our system to run on a lower signal-to-noise ratio.