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Solid-state Friction Stir Additive Manufacturing has recently gained attention as a result of its capacity to fabricate large-scale parts while preserving the mechanical properties of the feedstock material. However, the correlation between the quality of layer-by-layer bonding of the deposited metal and processing parameters has remained unknown. Neutron imaging techniques, with 90% total transmission per cm, are employed for Al6061 parts fabricated by MELD® Technology as a non-destructive evaluation approach for the first time to investigate the layer-by-layer structure of a stadium-shaped ingot in different sections. The post-processed results show the fabricated parts with an optimized set of processing parameters are void-free. However, the hydrocarbon-based feedstock lubricant segregates between the layers, which consequently may lead to non-uniform weaker mechanical properties along the build direction and stimulate crack initiation during mechanical loading. The tensile test results show 14% lower strain-to-failure values in alleged contaminated areas in transmission imaging results. Additionally, layer bonding is significantly impacted by hot-on-hot and hot-on-cold layer deposition schemes, especially for larger layer thicknesses. [ABSTRACT FROM AUTHOR]

We survey several neutron imaging and diffraction methods for non-destructive testing and evaluation of intact, commercial lithium-ion batteries. Specifically, far-field interferometry was explored as an option to probe a wide range of autocorrelation lengths within the batteries via neutron imaging. The dark-field interferometry images change remarkably from fresh to worn batteries, and from charged to discharged batteries. When attempting to search for visual evidence of battery degradation, neutron Talbot-Lau grating interferometry exposed battery layering and particle scattering through dark-field imaging. Bragg edge imaging also reveals battery wear and state of charge. Neutron diffraction observed chemical changes between fresh and worn, charged and discharged batteries. However, the utility of these methods, for commercial batteries, is dependent upon battery size and shape, with 19 to 43 mAh prismatic batteries proving most convenient for these experimental methods. This study reports some of the first spatially resolved, small angle scattering (dark-field) images showing battery degradation. [ABSTRACT FROM AUTHOR]

Abstract: The uptake of hydrogen by lanthanum pentanickel (LaNi5) to form lanthanum nickel hydride (LaNi5H6) is followed with three-dimensional imaging by neutron tomography. The hydrogen absorption process is slower than the time needed for acquiring a single radiograph, about 10s, but fast relative to the time to acquire a fully-sampled tomographic data set, about 6000s. A novel data acquisition scheme is used with angles based upon the Greek Golden ratio, a scheme which allows considerable flexibility in post-acquisition tomography reconstruction. Even with tomographic undersampling, the granular structure for the conversion of LaNi5 particles to LaNi5H6 particles is observed and visually tracked in 3D. Over the course of five sequential hydrogen uptake runs with various initial hydrogen pressures, some grains are repeatedly observed. [Copyright &y& Elsevier]

Purpose: Ion chamber dosimetry is being used to calibrate dose for cell irradiations designed to investigate photoactivated Auger electron therapy at the Louisiana State University Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. This study performed a dosimetry intercomparison for synchrotron-produced monochromatic x-ray beams at 25 and 35 keV. Ion chamber depth-dose measurements in a polymethylmethacrylate (PMMA) phantom were compared with the product of MCNP5 Monte Carlo calculations of dose per fluence and measured incident fluence. Methods: Monochromatic beams of 25 and 35 keV were generated on the tomography beamline at CAMD. A cylindrical, air-equivalent ion chamber was used to measure the ionization created in a 10 × 10 × 10-cm3 PMMA phantom for depths from 0.6 to 7.7 cm. The American Association of Physicists in Medicine TG-61 protocol was applied to convert measured ionization into dose. Photon fluence was determined using a NaI detector to make scattering measurements of the beam from a thin polyethylene target at angles 30°-60°. Differential Compton and Rayleigh scattering cross sections obtained from xraylib, an ANSI C library for x-ray-matter interactions, were applied to derive the incident fluence. MCNP5 simulations of the irradiation geometry provided the dose deposition per photon fluence as a function of depth in the phantom. Results: At 25 keV the fluence-normalized MCNP5 dose overestimated the ion-chamber measured dose by an average of 7.2 ± 3.0%-2.1 ± 3.0% for PMMA depths from 0.6 to 7.7 cm, respectively. At 35 keV the fluence-normalized MCNP5 dose underestimated the ion-chamber measured dose by an average of 1.0 ± 3.4%-2.5 ± 3.4%, respectively. Conclusions: These results showed that TG-61 ion chamber dosimetry, used to calibrate dose output for cell irradiations, agreed with fluence-normalized MCNP5 calculations to within approximately 7% and 3% at 25 and 35 keV, respectively. [ABSTRACT FROM AUTHOR]

Purpose: This work investigates the dose-response curves of GAFCHROMIC® EBT, EBT2, and EBT3 radiochromic films using synchrotron-produced monochromatic x-ray beams. EBT2 film is being utilized for dose verification in photoactivated Auger electron therapy at the Louisiana State University Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. Methods: Monochromatic beams of 25, 30, and 35 keV were generated on the tomography beamline at CAMD. Ion chamber depth-dose measurements were used to determine the dose delivered to films irradiated at depths from 0.7 to 8.5 cm in a 10 × 10 × 10-cm3 polymethylmethacrylate phantom. AAPM TG-61 protocol was applied to convert measured ionization into dose. Films were digitized using an Epson 1680 Professional flatbed scanner and analyzed using the net optical density (NOD) derived from the red channel. A dose-response curve was obtained at 35 keV for EBT film, and at 25, 30, and 35 keV for EBT2 and EBT3 films. Calibrations of films for 4 MV x-rays were obtained for comparison using a radiotherapy accelerator at Mary Bird Perkins Cancer Center. Results: The sensitivity (NOD per unit dose) of EBT film at 35 keV relative to that for 4-MV x-rays was 0.73 and 0.76 for doses 50 and 100 cGy, respectively. The sensitivity of EBT2 film at 25, 30, and 35 keV relative to that for 4-MV x-rays varied from 1.09-1.07, 1.23-1.17, and 1.27-1.19 for doses 50-200 cGy, respectively. For EBT3 film the relative sensitivity was within 3% of unity for all three monochromatic x-ray beams. Conclusions: EBT and EBT2 film sensitivity showed strong energy dependence over an energy range of 25 keV-4 MV, although this dependence becomes weaker for larger doses. EBT3 film shows weak energy dependence, indicating that it would be a better dosimeter for kV x-ray beams where beam hardening effects can result in large changes in the effective energy. [ABSTRACT FROM AUTHOR]

A microtomography beamline has been recently assembled and is currently operating at the Louisiana State University’s Center for Advanced Microstructures and Devices synchrotron (CAMD). It has been installed on a bending magnet white-light beamline at port 7A. With the storage ring operating at 1.5 GeV, this beamline has a maximum usable x-ray energy of ∼15 keV. The instrumentation consists of computer-controlled positioning stages for alignment and rotation, a CsI(Tl) phosphor screen, a reflecting mirror, a microscope objective (1:1, 1:4), and Linux/LabVIEW-controlled charge coupled device. With the 1:4 objective, the maximum spatial resolution is 2.25 μm. The positioning and image acquisition computers communicate via transfer control protocol/internet protocol (TCP/IP). A small G4/Linux cluster has been installed for the purpose of on-site reconstruction. Instrument, alignment and reconstruction programs are written in MATLAB, IDL, and C. The applications to date are many and we present several examples. Several biological samples have been studied as part of an effort on biological visualization and computation. Future improvements to this microtomography station include the addition of a double-multilayer monochromator, allowing one to evaluate the three-dimensional elemental composition of materials. Plans also include eventual installation at the CAMD 7 T wiggler beamline, providing x rays in excess of 50 keV to provide better penetration of higher mass-density materials. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: For certain porous media and initial conditions, constant flux infiltrations show a saturation profile which exhibits overshoot. This overshoot is the cause of gravity driven fingering, cannot be described by standard models of unsaturated flow, and is likely controlled by the exact nature of the pore filling at the initial front. Here we report synchrotron X-ray micro-tomography measurements of the porous medium and measure which pores are filled by water and air at the initial wetting front as a function of flux. We find that at high fluxes all the pores are filled with water; for intermediate fluxes, the pores along the edge of the column remain unsaturated; and for low fluxes the pores in the bulk of the experimental column remain unsaturated. This suggests that the unsaturated overshoot conditions observed at higher fluxes are primarily an edge effect of the column. The results can help delineate the correct continuum models that can capture overshoot and gravity driven fingering. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to compare dose measurements using ion chamber and radiochromic film dosimetry for a 35-keV synchrotron beam useful for Auger electron therapy. A 1.3-GeV electron beam, transported through a 3-pole superconducting wiggler magnet, produced a polychromatic photon beam from which a 35-keV beam (3.3mmAl HVL) was selected using a monochromator. A 2.8cm×2.5cm field was produced by vertically oscillating a polymethylmethacrylate phantom in which dose to water was measured as a function of depth. Charge, measured using a 0.23-cm3 cylindrical, air-equivalent ionization chamber, was converted to dose using American Association of Physicists in Medicine TG-61 protocol for 40–300kV X-ray beam dosimetry with minor assumptions. Optical density of radiochromic film (Gafchromic® EBT) was converted to dose using a 125kVp X-ray beam (2.9mmAl HVL) calibration curve. Fractional depth–dose curves measured using ion chamber and film agreed well with each other, the maximum difference being 4.5% at 8.85cm. Both agreed well with that predicted by MCNP5 Monte Carlo calculations. At 2.0-cm depth, film doses from five independent measurements predicted 0.952±0.022 of dose measured using the ion chamber. Dose measurements using two independent methods, ionization chamber and radiochromic film dosimetry, showed good agreement and should be suitable for future dosimetry necessary for cell and small animal irradiations. Improving agreement will require additional investigations of methods for converting ionization and film optical density to dose. [Copyright &y& Elsevier]

Purpose: To measure and compare Chinese hamster ovary cell survival curves using monochromatic 35-keV photons and 4-MV x-rays as a function of concentration of the radiosensitizer iododeoxyuridine (IUdR). Methods and Materials: IUdR was incorporated into Chinese hamster ovary cell DNA at 16.6 ± 1.9%, 12.0 ± 1.4%, and 9.2 ± 1.3% thymidine replacement. Cells were irradiated from 1 to 8 Gy with 35-keV synchrotron-generated photons and conventional radiotherapy 4-MV x-rays. The effects of the radiation were measured via clonogenic survival assays. Surviving fraction was plotted vs. dose and fit to a linear quadratic model. Sensitization enhancement ratios (SER10) were calculated as the ratio of doses required to achieve 10% surviving fraction for cells without and with DNA-incorporated IUdR. Results: At 4 MV, SER10 values were 2.6 ± 0.1, 2.2 ± 0.1, and 1.5 ± 0.1 for 16.6%, 12.0%, and 9.2% thymidine replacement, respectively. At 35 keV, SER10 values were 4.1 ± 0.2, 3.0 ± 0.1, and 2.0 ± 0.1, respectively, which yielded SER10 ratios (35 keV:4 MV) of 1.6 ± 0.1, 1.4 ± 0.1, and 1.3 ± 0.1, respectively. Conclusions: SER10 increases monotonically with percent thymidine replacement by IUdR for both modalities. As compared to 4-MV x-rays, 35-keV photons produce enhanced SER10 values whose ratios are linear with percent thymidine replacement and assumed to be due to Auger electrons contributing to enhanced dose to DNA. Although this Auger effectiveness factor is less than the radiosensitization factor of IUdR, both could be important for the clinical efficacy of IUdR radiotherapy. [ABSTRACT FROM AUTHOR]

Abstract: Dosimetry for Auger electron radiotherapy using monochromatic photon beams requires knowledge of beam characteristics. This study characterized a 35-keV photon beam generated at the LSU/CAMD synchrotron. Beam energy was measured by Compton spectroscopy and Si640c powder diffraction. Photon spatial distribution and virtual source position were measured using radiochromic film. Central-axis fluence was determined from Compton scattering measurements and application of the Klein–Nishina cross-section with percent polarization fit to results at 2–4 scattering angles. Broad-beam fluence was combined with MCNP5 Monte Carlo dose per fluence calculations to generate dose versus depth in a polymethylmethacrylate phantom, which was compared to ionization chamber and radiochromic film depth–dose measurements. For 22–41keV beams, diffraction-based and Compton-based energy measurements agreed to within −0.1±0.3 and 0.6±0.3keV, respectively, of monochromator calibrated energies. At 35keV and 0.66cm depth, dose uniformity over 80% of the 2.8cm×2.5cm beam varied from 105 to 78% of the central-axis value horizontally and from 90 to 100% vertically. Narrow-beam divergence yielded vertical and horizontal virtual source-to-surface distances of 3.8±0.2 and 15.7±1.0m, respectively. Incident fluence rates for a 35-keV beam (100mA ring current) ranged from 1.181±0.011×1011 to 3.053±0.004×1011 photonscm−2 s−1 with ≈100% polarization in the horizontal plane. Ion chamber and film dose measurements underestimated MCNP5-based dose by an average of 6.4±0.8 and 9.1±0.8%, respectively, over measured depths. These practical beam characterization methods should allow subsequent Monte Carlo dose calculations needed for planning future radiotherapy studies. Although simulated and measured depth–dose curves agree well in shape, improvement in absolute dose is desirable. [Copyright &y& Elsevier]

Underwriters Laboratories 94 test bars have been imaged with X-ray K-edge tomography between 12 and 32 keV to assess the bromine and antimony concentration gradient across char layers of partially burnt samples. Phase contrast tomography on partially burnt samples showed gas bubbles and dark-field scattering ascribed to residual blend inhomogeneity. In addition, single-shot grating interferometry was used to record X-ray movies of test samples during heating (IR and flame) intended to mimic the UL 94 plastics flammability test. The UL 94 test bars were formulated with varying concentrations of a brominated flame retardant, Saytex 8010, and a synergist, Sb2O3, blended into high-impact polystyrene (HIPS). Depending on the sample composition, samples will pass or fail the UL 94 plastics flammability test. Tomography and interferometry imaging show differences that correlate with UL 94 performance. Key features such as char layer, gas bubble formation, microcracks, and dissolution of the flame retardant in the char layer regions are used in understanding the efficiency of the flame retardant and synergist. The samples that pass the UL 94 test have a thick, highly visible char layer as well as an interior rich in gas bubbles. Growth of gas bubbles from flame-retardant thermal decomposition is noted in the X-ray phase contrast movies. Also noteworthy is an absence of bubbles near the burning surface of the polymer; dark-field images after burning suggest a microcrack structure between interior bubbles and the surface. The accepted mechanism for flame retardant activity includes free radical quenching in the flame by bromine and antimony species. The imaging supports this as well as provides a fast inspection of other parameters, such as viscosity and surface tension.

Grating-based X-ray and neutron interferometry tomography using phase-stepping methods generates large data sets. An improved algorithm is presented for solving for the parameters to calculate transmissions, differential phase contrast, and dark-field images. The method takes advantage of the vectorization inherent in high-level languages such as Mathematica and MATLAB and can solve a 16 × 1k × 1k data set in less than a second. In addition, the algorithm can function with partial data sets. This is demonstrated with processing of a 16-step grating data set with partial use of the original data chosen without any restriction. Also, we have calculated the reduced chi-square for the fit and notice the effect of grating support structural elements upon the differential phase contrast image and have explored expanded basis set representations to mitigate the impact.