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Author(s): H. Reichert (corresponding author) [1]; O. Klein [1]; H. Dosch [1]; M. Denk [1]; V. Honkimäki [3]; T. Lippmann [4]; G. Reiter [5] The local point symmetry of the [...]

Presently, a great amount of effort is being devoted to the development of CdTe and CdZnTe (CZT) detectors for a large variety of applications such as medical, industrial, and space research. We present the spectroscopic properties of some CZT crystals grown by the standard vertical Bridgman method and by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR (Parma, Italy). In this technique, the crystal is grown in an open quartz crucible fully encapsulated by a thin layer of liquid boron oxide. This method prevents contact between the crystal and the crucible, thereby allowing larger single grains with a lower dislocation density to be obtained. Several mono-electrode detectors were realized, with each having two planar gold contacts. The samples are characterized by an active area of about 7 mm × 7 mm and thicknesses ranging from 1 to 2 mm. The charge transport properties of the detectors have been studied by mobility-lifetime (μ × τ) product measurements, carried out at the European Synchrotron Radiation Facility (Grenoble, France) in the planar transverse field configuration, where the impinging beam direction is orthogonal to the collecting electric field. We have performed several fine scans between the electrodes with a beam spot of 10 μm × 10 μm at various energies from 60 to 400 keV. In this work, we present the test results in terms of the (μ × τ) product of both charge carriers. [ABSTRACT FROM AUTHOR]

A gamma-ray telescope mission concept based on Laue focusing methods is described. The studies have shown that a polarized beam has not changed its polarization level and direction after undergoing a small angle Laue diffraction inside a crystal.

A high-energy x-ray diffraction was used to perform in situ study and gain insight into the formation temperature and crystal structure of the rhombohedral phase [In.sub.4][Sn.sub.3][O.sub.12]. The linear and volume coefficients of thermal expansion determined for the [In.sub.4][Sn.sub.3][O.sub.12] phase describe the behavior of the entire [In.sub.4][Sn.sub.3][O.sub.12] transformation.

To date in astrophysics, X- and gamma-ray source emissions have been studied almost exclusively through imaging techniques, spectral- and timing-variability analysis. However, often two or more distinct models potentially describe the same observations of a particular celestial-radiation source. By measuring the angle and degree of linear polarization of the detected radiation, it is increased by two the number of observational parameters thereby allowing a better discrimination between different models. Therefore, future \gamma-ray-telescope instrumentation should include the capability to perform highly sensitive polarimetric measurements. This idea has recently become even more important from the perspective of new very sensitive hard X- and soft gamma-ray focusing missions based on Laue lenses such as the Gamma-Ray Imager and DUAL missions, submitted to ESA Cosmic Vision calls. In order to optimize the design of a gamma-ray telescope focal plane, a CdZnTe detector prototype has been tested at the European Synchrotron Radiation Facility under a \sim100\\% polarized gamma-ray beam. The tested detector was a 5 mm thick CdZnTe array with segmented anodes into 16\,\times\,16 pixels of 2.5\,\times\,2.5 mm^2. The aim of these tests was to study the polarimetric performance of this prototype as a function of the polarization state of the synchrotron beam. In particular, we determined the sensitivity of the detector to the level of the beam polarization as well as its potential to determine the polarization angle orientation by performing measurements at different polarization direction angles. In both tests the CdZnTe prototype showed a good linearity in its response and good sensitivity to polarization levels down to 50% and a polarization angular resolution better than 5^\circ. [ABSTRACT FROM AUTHOR]

The through thickness strain and depth resolved phase distribution in a dissimilar friction stir weld (FSW) of monolithic AA2024T3 to AA2014 + 34 vol.% Al2O3 is measured non-destructively. The measurements are performed using a novel strain and phase mapping technique. The technique is based on the use of a focused high- energy synchrotron beam, a novel spiral slit system, and an area detector system. The strong asymmetry of the calculated residual stress profiles is mainly due to the dominance of hydrostatic stresses in the metal matrix composite (MMC) side of the weld. Tensile stresses up to + 190 MPa are observed in the Al phase. The large residual stress gradient in the weld centre correlates with the weak mixing of the dissimilar plate materials. [ABSTRACT FROM AUTHOR]

Abstract: The atomic scale structure of explosive diamond nanoparticles has been studied using high-energy X-ray diffraction. The diffraction data have been converted to the real space representation in the form of the radial distribution function. Spherical and truncated octahedron nanodiamond clusters containing from 729 to 1182 atoms have been computer generated and then relaxed using the molecular dynamics method with the reactive empirical bond order potential for carbon-carbon interaction and the Lennard–Jones potential with parameters for inter-layer interactions. Validity of such constructed models has been verified by comparison of the simulations and the experimental data in both real and reciprocal space. The obtained results show that the structure of the investigated diamond nanoparticles cannot be satisfactorily described in terms of the model based on the perfect diamond lattice. The core-shell model with an average size of 22.5–23.4 Å, consisting of the diamond core and the graphite-like shell, accounts very well for the experimental data. [Copyright &y& Elsevier]

Abstract: High-energy X-ray diffraction has been used to study the structure of multi-wall carbon nanotubes, produced by template pyrolytic carbon deposition from thermal decomposition of propylene inside channels of an alumina membrane. X-ray diffraction intensities were measured on the powdered samples employing an image plate detector, integrated over the diffraction rings and converted to a radial distribution function by the Fourier transform. Defective hexagonal networks, generated by introducing the pentagon–heptagon pairs were rolled up to form regular cylinders and relaxed with a conjugate-gradient algorithm using the Brenner–Tersoff potential. A comparison of the simulated and experimental radial distribution functions shows that the model of the multi-wall carbon nanotubes, based on the defective nanotube structures, accounts very well for the experimental data. [Copyright &y& Elsevier]

We demonstrate the possibility to directly detect microgram amounts of the isotope 7 L i using a quasi-monochromatic high-energy photon beam. The isotope selective detection is based on a witness scatterer absorbing and re-emitting photons via nuclear resonance fluorescence. This enables the detection of isotopes with microgram accuracy at long distances from the actual sample. Further, we demonstrate that the technique can deliver quantitative information without specific knowledge of the photon flux and no spectral capabilities or knowledge of the resonance fluorescence cross section. Detection of low-atomic-weight isotopes screened by heavy shielding is also shown. The techniques described are applicable to all next-generation, ultrahigh brilliance, laser-Compton light sources currently under construction.

Rare-earth co-doping in inorganic materials has a long-held tradition of facilitating highly desirable optoelectronic properties for their application to the laser industry. This study concentrates specifically on rare-earth phosphate glasses, (R2O3)x(R'2O3)y(P2O5)(1-(x+y)), where (R, R') denotes (Ce, Er) or (La, Nd) co-doping and the total rare-earth composition corresponds to a range between metaphosphate, RP3O9, and ultraphosphate, RP5O14. Thereupon, the effects of rare-earth co-doping on the local structure are assessed at the atomic level. Pair-distribution function analysis of high-energy X-ray diffraction data (Q(max) = 28 Å(-1)) is employed to make this assessment. Results reveal a stark structural invariance to rare-earth co-doping which bears testament to the open-framework and rigid nature of these glasses. A range of desirable attributes of these glasses unfold from this finding; in particular, a structural simplicity that will enable facile molecular engineering of rare-earth phosphate glasses with 'dial-up' lasing properties. When considered together with other factors, this finding also demonstrates additional prospects for these co-doped rare-earth phosphate glasses in nuclear waste storage applications. This study also reveals, for the first time, the ability to distinguish between P-O and P[double bond, length as m-dash]O bonding in these rare-earth phosphate glasses from X-ray diffraction data in a fully quantitative manner. Complementary analysis of high-energy X-ray diffraction data on single rare-earth phosphate glasses of similar rare-earth composition to the co-doped materials is also presented in this context. In a technical sense, all high-energy X-ray diffraction data on these glasses are compared with analogous low-energy diffraction data; their salient differences reveal distinct advantages of high-energy X-ray diffraction data for the study of amorphous materials.

A time-resolved X-ray solution scattering study of bromine molecules in CCl(4) is presented as an example of how to track atomic motions in a simple chemical reaction. The structures of the photoproducts are tracked during the recombination process, geminate and non-geminate, from 100 ps to 10 micros after dissociation. The relaxation of hot Br(2)(*) molecules heats the solvent. At early times, from 0.1 to 10 ns, an adiabatic temperature rise is observed, which leads to a pressure gradient that forces the sample to expand. The expansion starts after about 10 ns with the laser beam sizes used here. When thermal artefacts are removed by suitable scaling of the transient solvent response, the excited-state solute structures can be obtained with high fidelity. The analysis shows that 30% of Br(2)(*) molecules recombine directly along the X potential, 60% are trapped in the A/A' state with a lifetime of 5.5 ns, and 10% recombine non-geminately via diffusive motion in about 25 ns. The Br-Br distance distribution in the A/A' state peaks at 3.0 A.

We have developed a new depth-graded multilayer system comprising W and SiC layers, suitable for use as hard x-ray reflective coatings operating in the energy range 100-200 keV. Grazing-incidence x-ray reflectance at E = 8 keV was used to characterize the interface widths, as well as the temporal and thermal stability in both periodic and depth-graded W/SiC structures, whereas synchrotron radiation was used to measure the hard x-ray reflectance of a depth-graded multilayer designed specifically for use in the range E approximately 150-170 keV. We have modeled the hard x-ray reflectance using newly derived optical constants, which we determined from reflectance versus incidence angle measurements also made using synchrotron radiation, in the range E = 120-180 keV. We describe our experimental investigation in detail compare the new W/SiC multilayers with both W/Si and W/B4C films that have been studied previously, and discuss the significance of these results with regard to the eventual development of a hard x-ray nuclear line telescope.