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Dual-energy computed tomography and the Alvarez and Macovski [Phys. Med. Biol. 21, 733 (1976)] transmitted intensity (AMTI) model were used in this study to estimate the maps of density (ρ) and atomic number (Z) of mineralogical samples. In this method, the attenuation coefficients are represented [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976)] in the form of the two most important interactions of X-rays with atoms that is, photoelectric absorption (PE) and Compton scattering (CS). This enables material discrimination as PE and CS are, respectively, dependent on the atomic number (Z) and density (ρ) of materials [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976)]. Dual-energy imaging is able to identify sample materials even if the materials have similar attenuation coefficients at single-energy spectrum. We use the full model rather than applying one of several applied simplified forms [Alvarez and Macovski, Phys. Med. Biol. 21, 733 (1976); Siddiqui et al., SPE Annual Technical Conference and Exhibition (Society of Petroleum Engineers, 2004); Derzhi, U.S. patent application 13/527,660 (2012); Heismann et al., J. Appl. Phys. 94, 2073-2079 (2003); Park and Kim, J. Korean Phys. Soc. 59, 2709 (2011); Abudurexiti et al., Radiol. Phys. Technol. 3, 127-135 (2010); and Kaewkhao et al., J. Quant. Spectrosc. Radiat. Transfer 109, 1260-1265 (2008)]. This paper describes the tomographic reconstruction of ρ and Z maps of mineralogical samples using the AMTI model. The full model requires precise knowledge of the X-ray energy spectra and calibration of PE and CS constants and exponents of atomic number and energy that were estimated based on fits to simulations and calibration measurements. The estimated ρ and Z images of the samples used in this paper yield average relative errors of 2.62% and 1.19% and maximum relative errors of 2.64% and 7.85%, respectively. Furthermore, we demonstrate that the method accounts for the beam hardening effect in density (ρ) and atomic number (Z) reconstructions to a significant extent. [ABSTRACT FROM AUTHOR]

We have used time-resolved X-ray diffraction to monitor the resolidification process of molten InSb. Melting was induced by an ultra-short laser pulse and the measurement conducted in a high-repetition-rate multishot experiment. The method gives direct information about the nature of the transient regrowth and permanently damaged layers. It does not rely on models based on surface reflectivity or second harmonic generation (SHG). The measured resolidification process has been modeled with a 1-D thermodynamic heat-conduction model. Important parameters like sample temperature, melting depth and amorphous surface layer thickness come directly out of the data, while mosaicity of the sample and free carrier density can be quantified by comparing with models. Melt depths up to 80 nm have been observed and regrowth velocities in the range 2–8 m/s have been measured. [ABSTRACT FROM AUTHOR]

The structures of films of pulmonary surfactant protein B (SP-B) and mixtures of SP-B and dipalmitoylphosphatidylcholine (DPPC) at the air/water interface have been studied by neutron reflectometry and Langmuir film balance methods. From the film balance studies, we observe that the isotherms of pure DPPC and SP-B/DPPC mixtures very nearly overlay one another at very high pressures, suggesting that the SP-B is being excluded from the film. The use of multiple contrasts with neutron reflectometry at a range of surface pressures has enabled the mixing and squeeze out of the DPPC and SP-B mixtures to be studied. We can identify the SP-B component of the interfacial structure and its position as a function of surface pressure. The mixtures are initially a homogeneous layer at low surface pressures. At higher surface pressures, the SP-B is squeezed out of the lipid layer into the subphase, with the first signs detected at 30 mN m(-1). At 50 mN m(-1), the subphase is almost completely excluded from the DPPC layer, with the SP-B content significantly reduced. Only a small amount of DPPC appears to be associated with the squeezed out SP-B.

Examinations of bremsstrahlung and energetic electron beams from a novel laser plasma source motivate and assist characterization of a backthinned, backilluminated direct detection x-ray charge-coupled device (CCD), a topology that is uncommon in hard x-ray work. Behavior toward pseudomonochromatic ((55)Fe) and multichromatic ((241)Am) sources is briefly reviewed under optimized noise conditions. Results collectively establish the previously unknown functional depth structure. Several modes of usage are illustrated in approximately 4-20 keV x-ray laser plasma source investigations, where the significance of the characterization is briefly discussed. The spectral redistribution associated with this CCD topology is unfavorable, yet appropriate analysis ensures that sufficient spectral information remains for quantitative determination of broadband x-ray flux and spectra in essentially single laser shot measurements. The energy dependence of nascent electron cloud radii in silicon is determined using broadband x-rays from the laser plasma source, turning the narrow depletion depth to advantage. Finally, the characterization is used to quantify recent x-ray spectral explorations of the water jet laser plasma source operating under aspirator vacuum. These results will have key value for establishment of laboratory based ultrafast extended x-ray absorption fine structure experiments using microbolometric detectors.

A plasma source free from characteristic emission lines is described, based on laser irradiation of a water jet in a helium atmosphere. Various key aspects of the laser interaction are presented along with practical characterization of the observed isotropic approximately 4-10 keV x-ray emissions, measurements of which indicate subpicosecond duration. Observations are consistent with a vacuum heating plasma mechanism at the helium-water interface and indicate strong potential for in-house ultrafast chemical structure dynamics application when coupled to contemporary detector developments.

Instrumentation for stroboscopic time-resolved diffraction studies at low temperatures is described. Exciting laser light is delivered to the crystal through an optical fiber. During the diffraction experiment, fluorescence from the sample is focused onto a fiber optic bundle surrounding the laser-light fiber, and monitored by a photodiode. A rotating slotted disk produces a pulsed X-ray beam with pulse frequencies suitable for the study of molecular excited states with lifetimes of 10 micros or longer. Synchronization of the laser-pump/X-ray-probe pulses is achieved through a trigger signal from a photosensor mounted on the rotating disk, or from an X-ray sensitive photodiode inserted in the beamstop. For the study of shorter-lived species the time structure of the synchrotron beam is to be used. Equations are derived for the maximum and average fractional excited-state populations as a function of lifetime, pulse frequency and the fraction of molecules being excited by the laser pulse.