Public Reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comment regarding this burden estimates or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and Abstract. The use of severe plastic deformation techniques such as equal channel angular pressing, has been shown to refine metal microstructures giving advantageous mechanical properties. Metals and alloys subjected to ECAP procedures can have very high yield strengths while maintaining substantial ductility, a unique and attractive combination. However, the implicitly large deformations (the application of repeated shear strains of ~1 are typical) make prediction of the resulting mechanical properties difficult. In particular, modeling the polycrystalline texture evolution and microstructural strain response is challenging. In this paper, results are presented from a neutron diffraction study on aluminum, copper, nickel and beryllium processed by ECAP. Specific attention is given to the evolution of the bulk texture after one pass and the effect of the initial texture. The neutrons probed volumes on the order of cubic centimeters and therefore provided texture and strain information averaged over the bulk of the sample. The results are discussed in the context of a visco-plastic selfconsistent model.
Tools for three-dimensional elemental characterization are available on length scales ranging from individual atoms, using electrons as a probe, to micrometers with X-rays. However, for larger volumes up to millimeters or centimeters, quantitative measurements of elemental or isotope densities were hitherto only possible on the surface. Here, a novel quantitative elemental characterization method based on energy-resolved neutron imaging, utilizing the known neutron absorption cross sections with their ‘finger-print’ absorption resonance signatures, is demonstrated. Enabled by a pixilated time-of-flight neutron transmission detector installed at an intense short-pulsed spallation neutron source, for this demonstration 3.25 million state-of-the-art nuclear physics neutron transmission analyses were conducted to derive isotopic densities for five isotopes in 3D in a volume of 0.25 cm3. The tomographic reconstruction of the isotope densities provides elemental maps similar to X-ray microprobe maps for any cross-section in the probed volume. The bulk isotopic density of a U-20Pu-10Zr-3Np-2Am nuclear transmutation fuel sample was measured, agrees well with mass-spectrometry and is evidence of the accuracy of the method.
3D visualization of x-ray computed tomography (CT) has revolutionized the study of paleontology over the last decade by allowing paleontologists to gain essential insights into the anatomy, development and preservation of important specimens. Neutron computed tomography (NT) is an exciting new frontier in 3D visualization that has only rarely been applied to vertebrate fossils. NT is based on the interaction of neutrons and the nuclei of materials and thus is able to reveal internal detail in fossils impregnated with dense minerals otherwise impervious to traditional CT, and can also be used to distinguish areas of distinct elemental or isotopic composition within fossils. We have applied high resolution CT and NT to two specimens, the skull of the holotype of the Cretaceous tyrannosauroid Bistahieversor sealeyi (NMMNH P-27469) and a nearly complete skull of the Paleocene phenacodontid "condylarth" mammal Tetraclaenodon puercensis (NMMNH P-69898) using the unique capabilities of the Los Alamos Neutron Science Center (LANSCE) at Los Alamos National Laboratory (LANL), New Mexico. To reduce attenuation of neutrons and x-rays a special carbon fiber composite, rather than plaster, support jacket was constructed to hold the Bistahieversor skull. The CT scan of the Bistahieversor skull used 10 MeV x-rays at 200 μm resolution. This is the highest resolution CT of an entire large (> 1m long) tyrannosauroid skull ever made. Both specimens were also scanned using high-energy or low-energy (thermal) neutrons. Preliminary NT results reveals details of the internal bone structure of both specimens not readily visible with CT, with no residual increased radiation level following the cool-off period. CT and NT showed that Bistahieversor possesses the extensive tympanic sinuses and elongate, tubular endocast that were once thought to diagnose only the largest-bodied, most derived tyrannosaurids like T. rex, whereas Tetraclaenodon has an endocast that was not as proportionally large, and overall more primitive, than the brains of modern placentals.
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