Purpose: Tomography using diffracted x-rays produces reconstructions mapping quantities such as crystal lattice parameter(s), crystallite size, and crystallographic texture, information quite different from that obtained with absorption or phase contrast. Diffraction tomography is used to map an entire blue shark centrum with its double cone structure (corpora calcerea) and intermedialia (four wedges).
Approach: Energy dispersive diffraction (EDD) and polychromatic synchrotron x-radiation at 6-BM-B, the Advanced Photon Source, were used. Different, properly oriented Bragg planes diffract different x-ray energies; these intensities are measured by one of ten energy-sensitive detectors. A pencil beam defines the irradiated volume, and a collimator before each energy-sensitive detector selects which portion of the irradiated column is sampled at any one time. Translating the specimen along X , Y, and Z axes produces a 3D map.
Results: We report 3D maps of the integrated intensity of several bioapatite reflections from the mineralized cartilage centrum of a blue shark. The c axis reflection’s integrated intensities and those of a reflection with no c axis component reveal that the cone wall’s bioapatite is oriented with its c axes lateral, i.e., perpendicular to the backbone’s axis, and that the wedges’ bioapatite is oriented with its c axes axial. Absorption microcomputed tomography (laboratory and synchrotron) and x-ray excited x-ray fluorescence maps provide higher resolution views.
Conclusion: The bioapatite in the cone walls and wedges is oriented to resist lateral and axial deflections, respectively. Mineralized tissue samples can be mapped in 3D with EDD tomography and subsequently studied by destructive methods.
Tomography using diffracted x-rays produces reconstructions mapping quantities including crystal lattice parameter(s), crystallite size and crystallographic texture; this information is quite different from that obtained with absorption contrast or phase contrast. Diffraction tomography can be performed using energy dispersive diffraction (EDD) and polychromatic synchrotron x-radiation. In EDD, different, properly-oriented Bragg planes diffract different x-ray energies; these intensities are measured by an energy sensitive detector. A pencil beam defines the irradiated volume, and a collimator before the energy sensitive detector selects which portion of the irradiated column is sampled at any one time. A 3D map is assembled by translating the specimen along X, Y and Z axes. This paper reports results of 3D mapping of the integrated intensity of several reflections from the bioapatite in the mineralized cartilage centrum of a blue shark. The multiple detector EDD system at 6-BM-B, the Advanced Photon Source was used to map an entire blue shark centrum. The shark centrum consists of a double cone structure (corpora calcerea) supported by the intermedialia consisting of four wedges. The integrated intensities of the c-axis reflection and of a reflection with no c-axis component reveals the bioapatite within the cone wall is oriented with its c-axes lateral, i.e., perpendicular to the axis of the backbone, whereas the bioapatite within the wedges is oriented with its c-axes axial. Results of absorption microCT (laboratory and synchrotron) and x-ray excited x-ray fluorescence mapping are included to provide higher resolution data of the structures underlying the EDD maps. Application of EDD tomography to 3D mapping of large specimens promises to add to the understanding of other mineralized tissue samples which cannot be sectioned.
Applications of neutron diffraction for small samples (<1mm3) or small fiducial areas are limited by the
available neutron flux density. Recent demonstrations of convergent beam electron and x-ray diffraction and focusing of cold (λ>1 Å) neutrons suggest the possibility to use convergent beam neutron diffraction for small sample crystallography. We have carried out a systematic study of diffraction of both monoenergetic and broad bandwidth
neutrons at the NIST Research Reactor and at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory. Combining convergent beams with time-of-flight Laue diffraction is particularly attractive for high efficiency small sample diffraction studies. We have studied single crystal and powder diffraction of neutrons with convergence angles as large as 15° and have observed diffracted peak intensity gains greater than 20. The convergent beam method (CBM) shows promise for crystallography on small samples of small to medium size molecules (potentially even for proteins), ultra-high pressure samples, and for mapping of strain and texture distributions in larger samples.
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