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The near-nozzle structure of several nonevaporating biodiesel-blend sprays has been studied using X-ray radiography. Radiography allows quantitative measurements of the fuel distribution in sprays to be made with high temporal and spatial resolution. Measurements have been made at different values of injection pressure, ambient density, and with two different nozzle geometries to understand the influences of these parameters on the spray structure of the biodiesel blend. These measurements have been compared with corresponding measurements of Viscor, a diesel calibration fluid, to demonstrate the fuel effects on the spray structure. Generally, the biodiesel-blend spray has a similar structure to the spray of Viscor. For the nonhydroground nozzle used in this study, the biodiesel-blend spray has a slightly slower penetration into the ambient gas than the Viscor spray. The cone angle of the biodiesel-blend spray is generally smaller than that of the Viscor spray, indicating that the biodiesel-blend spray is denser than the Viscor spray. For the hydroground nozzle, both fuels produce sprays with initially wide cone angles that transition to narrow sprays during the steady-state portion of the injection event. These variations in cone angle with time occur later for the biodiesel-blend spray than for the Viscor spray, indicating that the dynamics of the injector needle as it opens are somewhat different for the two fuels. [DOI: 10.1115/1.3094023]

X-ray phase-contrast imaging is a potential nondestructive testing and diagnostic technology in medicine, biology and materials science. It provides high sensitivity and contrast of weakly absorbing Iow-Z objects by measuring phase shifts of the X-rays. In this paper, we propose a novel phase-contrast imaging method using only one absorption grating and a high-resolution detector. The intensity distribution downstream of the grating is recorded and analyzed by the high-resolution detector directly. We use a spatial phase demodulation method to retrieve the phase information. Only one image is needed. Numerical simulations are performed to validate that the setup of our method is greatly simplified compared with the phase-stepping method and our method can significantly reduce the time-consuming and the unnecessary dose. Index Terms--Phase contrast, phase measurement, spatial phase demodulation, X-ray imaging.

The terbium-activated yttrium tantalite (YTa[O.sub.4]:[Tb.sup.3+]) phosphor is of great interest due to the interesting spectroscopic properties of rare earth ions in crystals and also practical use in x-ray imaging. Using the group-theoretical approach, we analyze the selection rules for the transition between Stark components of [Tb.sup.3+] in symmetry of the actual crystal field and the polarization for the allowed transitions. The luminescence upon UV, vacuum-ultraviolet (VUV), and x-ray excitation is presented and discussed. The YTa[O.sub.4]:[Tb.sup.3+] phosphors are found to be efficient VUV-excited luminescent materials that could be used not only in x-ray intensifying screens, but also in mercury-free fluorescent lamps or plasma display panels. OCIS codes: 160.2540, 260.3800, 260.5430, 300.6560, 300.6540, 300.6550.

X-ray coherence evolution in the imaging process plays a key role for x-ray phase-sensitive imaging. In this work we present a phase-space formulation for the phase-sensitive imaging. The theory is reformulated in terms of the cross-spectral density and associated Wigner distribution. The phase-space formulation enables an explicit and quantitative account of partial coherence effects on phase-sensitive imaging. The presented formulas for x-ray spectral density at the detector can be used for performing accurate phase retrieval and optimizing the phase-contrast visibility. The concept of phase-space shearing length derived from this phase-space formulation clarifies the spatial coherence requirement for phase-sensitive imaging with incoherent sources. The theory has been applied to x-ray Talbot interferometric imaging as well. The peak coherence condition derived reveals new insights into three-grating-based Talbot-interferometric imaging and gratings-based x-ray dark-field imaging. OCIS codes: 110.1650, 030.1670.

We present a new algorithm which merges discontinuities in 3-D images of tubular structures presenting undesirable gaps. The application of the proposed method is mainly associated to large 3-D images of microvascular networks. In order to recover the real network topology, we need to fill the gaps between the closest discontinuous vessels. The algorithm presented in this paper aims at achieving this goal. This algorithm is based on the skeletonization of the segmented network followed by a tensor voting method. It permits to merge the most common kinds of discontinuities found in microvascular networks. It is robust, easy to use, and relatively fast. The microvascular network images were obtained using synchrotron tomography imaging at the European Synchrotron Radiation Facility. These images exhibit samples of intracortical networks. Representative results are illustrated. Index Terms--Gap filling, skeleton, tensor voting, vessel extraction, X-ray imaging.

The dynamic lateral polarization and charge steering effect was studied in 2D pixilated CdZnTe monolithic detector arrays designed for high flux x-ray imaging applications. While these detectors have shown the ability to work at 15 x [10.sup.6] counts/s/[mm.sup.2] and higher count-rates in pulse mode, we observed some detectors that exhibited a dynamic lateral polarization and charge steering effect causing non-uniform spatial response to the radiation field. The dynamic nature of the effect is shown by its flux dependence and reversibility upon changing the x-ray flux without a requirement to turn off the bias voltage. The effect causes the induced charge that would normally move from the cathode towards the anode to instead move laterally causing counts to shift away from a flux boundary. We show that the effect is not related to the physical boundary of the detector but rather related to the boundary of the irradiated area of the device. The dynamic polarization and charge steering effect can be attributed to the limited hole transport in the bulk material causing a buildup of a dynamic space-charge region under the irradiated area. The resulting lateral (perpendicular to the irradiation direction) electric field causes the lateral drift (steering) of the x-ray injected charge clouds. The static version of such lateral steering is often observed for charged structural defects in CdZnTe crystals. The studied 2D CdZnTe monolithic arrays were 16 x 16pixel devices having 0.4 mm x 0.4 mm area pixels on a 0.5 mm pitch and were fabricated using 8.7 mm x 8.7 mm x 3.0 mm CdZnTe single crystals grown by the high-pressure electro-dynamic gradient freeze technique. The devices were probe tested in a system consisting of a custom 16 x 16 pin probe head, 256 channel read-out electronics utilizing 8-channel fast bipolar ASIC chips, and a computer controlled 120 kVp x-ray source. Index Terms--CdZnTe, polarization, semiconductor radiation detectors, x-ray detectors, x-ray imaging.

We report here on self-magnetic-pinch diode experiments at voltages from 3.5 to 6 MV. In addition to electrical diagnostics, the diode is characterized as a radiation source by dose and spot-size measurement. As the operating voltage increases, we find that a given diode geometry tends to produce a smaller spot but suffers from the reduced impedance lifetime. Optimization involves increasing the cathode diameter and diode gap as the voltage increases. We find a good quantitative agreement with the Monte Carlo code integrated tiger series over the entire data set, assuming an effective electron incidence angle of 20[degrees]. Over this range, we observe favorable dose and spot scaling of optimized diode performance with voltage. Our best results are roughly 200-rad CaF2 at 1 m with an ~2-mm-diameter spot. These were obtained at diode parameters of roughly 6 MV, 150 kA, and 30-ns radiation full-width at half-maximum. Index Terms--Electron beams, particle beams, pinched-beam diodes, pulsed power, radiography.

The luminescence of [(Lu, Y).sub.2]Si[O.sub.5]: Ce (LYSO:Ce) and [Gd.sub.2]Si[O.sub.5]: Ce (GSO:Ce) crystals was studied for use in tomographic medical x-ray imaging. LYSO:Ce and GSO:Ce are high density (7.1 g/[cm.sup.3] and 6.71 g/[cm.sup.3] respectively), high atomic number (71 for Lu and 64 for Gd), non-hydroscopic, and short decay time (40 ns and 60 ns respectively) scintillators. Evaluation was performed by determining: 1) the luminescence efficiency (LE) (emitted fight energy flux over incident x-ray energy flux) in x-ray energies employed in general x-ray imaging (40-140 kVp) and in mammographic x-ray imaging (22-49 kVp), 2) the fight emission spectrum, determined at various x-ray energies (22-140 kVp), and 3) the spectral compatibility to optical photon detectors, incorporated in medical imaging systems. Both scintillation materials exhibited adequately high LE in the x-ray diagnostic energy range, with LYSO:Ce's LE being distinctively higher. LYSO:Ce and GSO:Ce were found most compatible with the S-20 photocathode (0.9 for both materials) and adequately compatible to the amorphous silicon photodiode (0.74 for both materials), incorporated in many digital x-ray detectors. Index Terms--Inorganic scintillators, luminescence efficiency, LYSO:Ce, matching factor, radiation detectors.

This work describes an investigation on the use of polymeric blends as the host material in flexible thermoluminescent (TL) films, for application in digital radiography. Polymeric films made of semi-crystalline poly(vinylidene fluoride--trifluorethylene) [P(VDF-TrFE)] copolymer blended with 0, 5, 10, 15, 25, 30, and 35% wt. of amorphous poly(methyl methacrylate) [PMMA] were studied using Differential Scanning Calorimetry (DSC) and UV-VIS spectrometry. Combining data from blend compatibility and melting temperature of the crystallites, we found out that the P(VDF-TrFE)/PMMA with contents of PMMA until 15% wt. can be used for hosting thermoluminescent materials. Above this value, there is no more compatibility between these materials, with the appearance of small clusters of PMMA. Among the candidates, the blend with 15% wt. shows the best optical transparence and thus it has been chosen as the optimal blend composition for use as host matrix in a TL film, once the thermoluminescent visible light emitted from the granules localized beneath the film surface has a higher probability of getting outside, without optical scattering. Digital radiographic images emitted from heated films made of CaS[O.sub.4]:Mn storage phosphor powder dispersed into these blends were captured using a standard charged coupled device (CCD). The quality of the obtained radiographic images shows that TL plastic films present high potential to be an alternative way to obtain digital images, commonly obtained by photoluminescence based devices or X ray sensitive CCD cameras. Index Terms--Radiation detectors, thermoluminescence, digital imaging, plastic films, radiography, P(VDF-TrFE) copolymers, P(VDF-TrFE)/PMMA blends.