X-ray single crystal and powder diffraction: possibilities and applications

In this article the main possibilities of single crystal and powder diffraction analysis using conventional laboratory x-ray sources are introduced. Several examples of applications with different solid samples and in different fields of applications are shown illustrating the multidisciplinary capabilities of both techniques.

Les fractures du pilon tibial. Etude rétrospective à long terme de 51 fractures traitées par réduction sanglante et ostéosynthèse [Fractures of the tibial pilon. Long-term retrospective study of 51 fractures treated with open reduction and osteosynthesis].

PURPOSE OF THE STUDY: Fracture of the tibial pilon is a rare injury and its treatment remains difficult. The aim of this study was to report the complications and long term results of internal fixation using a technique which respects soft tissues and in which little material was used. MATERIAL: From 1985 to 1990, 48 patients with 51 fractures of the tibial pilon were treated by open reduction and internal fixation. All patients were submitted to a clinical and radiological review. METHODS: Both the Rüedi/Allgöwer and the AO-classification were used and determined by standard X-rays. Surgical procedure was performed with a 2 or 3 1/3 tube AO-plates and the peroneus was always fixed if fractured. Intraoperative reconstruction was analyzed. Subjective and objective scoring were used according to Olerud and Molander and the ankle arthritis was scored according to the classification determined by the SOFCOT in 1992. RESULTS: A minimal follow-up of 1 year for all cases was obtained, based on our own files. Thirty-eight patients (40 fractures) were evaluated after an average period of 88 months (56 to 124 months). Five patients developed cutaneous infection, three developed deep infection and four developed superficial skin necrosis. One aseptic non-union necessitated reoperation after 14 months. Two ankles had joint fusion after 19 and 25 months respectively due to severe arthritis. In six cases infectious and non-infectious complications led to surgical revision. According to the Olerud and Molander score, 15 per cent of the results were excellent, 45 per cent were good, 30 per cent were fair and 10 per cent poor. DISCUSSION: Literature shows a wide range of results following this surgical procedure. This is due to the difference in the type of trauma, classification system used, material used for the internal fixation and method of evaluation. The classification system of Rüedi and Allgöwer is the most commonly used but has a rather subjective tendency, especially between type II and type III. Treatment is difficult, especially for comminutive fractures associated with soft tissue damage. In this case, open reduction and internal fixation could increase iatrogenic lesions. For this reason surgical procedure can be delayed for several days, little material is used and soft tissue manipulation is reduced to minimum. In other study reports, the use of external fixation with or without minimal internal fixation have produced less complications without improving long term results. CONCLUSION: Analysis and comparison of study reports are difficult because of the absence of consensus in classification system and evaluation methods. The AO-classification, apparently the most objective, will probably be more and more used in the future. Treatment must be adapted to the bony lesion and soft tissue damage. Open reduction and internal fixation must be reserved for a specific group of lesion.

On the multiwavelength spectrum of the microquasar 1E1740.7-2942

The microquasar 1E 1740.7-2942 is a source located in the direction of the Galactic Center. It has been detected at X-rays, soft gamma-rays, and in the radio band, showing an extended radio component in the form of a double-sided jet. Although no optical counterpart has been found so far for 1E 1740.7-2942, its X-ray activity strongly points to a galactic nature. Aims.We aim to improve our understanding of the hard X-ray and gamma-ray production in the system, exploring whether the jet can emit significantly at high energies under the light of the present knowledge. Methods.We have modeled the source emission, from radio to gamma-rays, with a cold-matter dominated jet model. INTEGRAL data combined with radio and RXTE data, as well as EGRET and HESS upper-limits, are used to compare the computed and the observed spectra. Results.From our modeling, we find out that jet emission cannot explain the high fluxes observed at hard X-rays without violating at the same time the constraints from the radio data, favoring the corona origin of the hard X-rays. Also, 1E 1740.7-2942 might be detected by GLAST or AGILE at GeV energies, and by HESS and HESS-II beyond 100 GeV, with the spectral shape likely affected by photon-photon absorption in the disk and corona photon fields.

Microquasar models for 3EG J1828+0142 and 3EG J1735-1500

Microquasars are promising candidates to emit high-energy gamma-rays. Moreover, statistical studies show that variable EGRET sources at low galactic latitudes could be associated with the inner spiral arms. The variable nature and the location in the Galaxy of the high-mass microquasars, concentrated in the galactic plane and within 55 degrees from the galactic center, give to these objects the status of likely counterparts of the variable low-latitude EGRET sources. We consider in this work the two most variable EGRET sources at low-latitudes: 3EG J1828+0142 and 3EG J1735-1500, proposing a microquasar model to explain the EGRET data in consistency with the observations at lower energies (from radio frequencies to soft gamma-rays) within the EGRET error box.

Caracterizacion por difraccion de rayos-X, analisis termico y espectroscopia Raman de los cristales mixtos Li(NH4)(1-x)KxSO4

En este trabajo se estudia la preparació n y caracterizació n de las fases de los cristales mixtos de f órmula Li(NH4)1-xKxSO4. La caracterizacói n se ha efectuado por aná lisis té rmico con DSC y ATD, difracci ón de rayos-X sobre polvo cristalino con temperatura variable, difracci n de rayos-X sobre muestra monocristalina a temperatura variable a fin de determina su estructura cristalina y por espectroscop"a Raman a temperatura variable. Se han obtenido dos tipos de fases. Una soluci n s lida con 0.94 < x < 1 que presenta los mismos tipos estructurales que el LiKSO4, pero seg n el m todo de cristalizaci n pueden aparecer nuevas fases que no presenta el LiKSO4. El segundo tipo de compuesto tiene por f rmula Li(NH4)0.53K0.47SO4, el cual presenta una estructura hexagonal con par metro a » 3 aLiKSO4. Este compuesto tiene por encima de la temperatura ambiente una sola transici n a 463K.

Monte Carlo simulation of x-ray spectra generated by kilo-electron-volt electrons

We present a general algorithm for the simulation of x-ray spectra emitted from targets of arbitrary composition bombarded with kilovolt electron beams. Electron and photon transport is simulated by means of the general-purpose Monte Carlo code PENELOPE, using the standard, detailed simulation scheme. Bremsstrahlung emission is described by using a recently proposed algorithm, in which the energy of emitted photons is sampled from numerical cross-section tables, while the angular distribution of the photons is represented by an analytical expression with parameters determined by fitting benchmark shape functions obtained from partial-wave calculations. Ionization of K and L shells by electron impact is accounted for by means of ionization cross sections calculated from the distorted-wave Born approximation. The relaxation of the excited atoms following the ionization of an inner shell, which proceeds through emission of characteristic x rays and Auger electrons, is simulated until all vacancies have migrated to M and outer shells. For comparison, measurements of x-ray emission spectra generated by 20 keV electrons impinging normally on multiple bulk targets of pure elements, which span the periodic system, have been performed using an electron microprobe. Simulation results are shown to be in close agreement with these measurements.

Raios-x: fascinação, medo e ciência

This work presents the discovery and the use of x-rays at the end of the XIXth and the beginning of the XXth century. X-rays greatly impacted science and everyday life. Their existence broke the idea that knowledge had reached a limiting step. In general, people regarded x-rays as a marvel of science, but reactions against their use were also found. Several applications were proposed, especially in medicine. However, little or no attention was paid to security measures, leading to health damages and even death. The development of the radiological protection took into account the accidents with the x-rays.

Sistema para realização de medidas de luminescência com excitação por Raios X

In this work is presented a versatile system for X-ray excited optical luminescence (XEOL) measurements. The apparatus was assembled from a sample holder connected to an optical fiber responsibly for the acquisition of the scintillation signal. The spectrum is registered with a CCD coupled in a spectrograph provided with diffraction gratings. The system performance was analyzed by exciting GdAlO3:Eu3+ 3.0 at.% with X-rays from a diffractometer and measuring the emission spectra. The system can be used to obtain precise and reliable spectroscopic properties of samples with various conformations without the loss of the required safety when dealing with ionizing radiations.

Very High Energy Gamma-Rays emitting BL LAC's Population Study

Context: BL Lacs are the most numerous extragalactic objects which are detected in Very High Energy (VHE) gamma-rays band. They are a subclass of blazars. Large flux variability amplitude, sometimes happens in very short time scale, is a common characteristic of them. Significant optical polarization is another main characteristics of BL Lacs. BL Lacs' spectra have a continuous and featureless Spectral Energy Distribution (SED) which have two peaks. Among 1442 BL Lacs in the Roma-BZB catalogue, only 51 are detected in VHE gamma-rays band. BL Lacs are most numerous (more than 50% of 514 objects) objects among the sources that are detected above 10 GeV by FERMI-LAT. Therefore, many BL Lacs are expected to be discovered in VHE gamma-rays band. However, due to the limitation on current and near future technology of Imaging Air Cherenkov Telescope, astronomers are forced to predict whether an object emits VHE gamma-rays or not. Some VHE gamma-ray prediction methods are already introduced but still are not confirmed. Cross band correlations are the building blocks of introducing VHE gamma-rays prediction method. Aims: We will attempt to investigate cross band correlations between flux energy density, luminosity and spectral index of the sample. Also, we will check whether recently discovered MAGIC J2001+435 is a typical BL Lac. Methods: We select a sample of 42 TeV BL Lacs and collect 20 of their properties within five energy bands from literature and Tuorla blazar monitoring program database. All of the data are synchronized to be comparable to each other. Finally, we choose 55 pair of datasets for cross band correlations finding and investigating whether there is any correlation between each pair. For MAGIC J2001+435 we analyze the publicly available SWIFT-XRT data, and use the still unpublished VHE gamma-rays data from MAGIC collaboration. The results are compared to the other sources of the sample. Results: Low state luminosity of multiple detected VHE gamma-rays is strongly correlated luminosities in all other bands. However, the high state does not show such strong correlations. VHE gamma-rays single detected sources have similar behaviour to the low state of multiple detected ones. Finally, MAGIC J2001+435 is a typical TeV BL Lac. However, for some of the properties this source is located at the edge of the whole sample (e.g. in terms of X-rays flux). Keywords: BL Lac(s), Population study, Correlations finding, Multi wavelengths analysis, VHE gamma-rays, gamma-rays, X-rays, Optical, Radio

The measured variation of the Debye-Waller factor of aluminum from 295K to 815K by using the energy dispersive x-ray diffraction technique

The Energy Dispersive X-ray Diffraction System at Brock University has been used to measure the intensities of the diffraction lines of aluminum powder sample as a function of temperature. At first, intensity measurements at high temperature were not reproducible. After some modifications have been made, we were able to measure the intensities of the diffraction lines to 815K, with good accuracy and reproducibility. Therefore the changes of the Debye-Waller factor from room temperature up to 815K for aluminum were determined with precision. Our results are in good agreement with those previously published.

X-ray diffraction studies of muscle : observations on the anterior byssus retractor muscle of Mytilus edulis and the insect flight muscle from Sarcophaga bullata

The interfilament spacing of the anterior byssus retractor muscle from Mytilus edulis was studied as the muscle was extended. It was found that variations in this spacing were very small and consistent with the hypothesis that the interfilament spacing was independent of the extension of the muscle. It was observed that the interfilament spacing was dependent on the osmolarity of the bathing medium. In concentrated solutions of the artificial seawater, the interfilament spacing decreased; while in dilute solutions of artificial seawater, it was observed that the interfilament spacing was increasing. X-ray diffraction patterns were obtained from fresh, and glutaraldehyde fixed, specimens of insect flight muscle from Sarcophaga bullata. There patterns were in general agreement with previous X-ray diffraction studies of insect flight muscle. A reflexion G at 93A was observed and interpreted as arising from diffraction in the mitochondria. Specimens of dried insect flight muscle produced a diffraction pattern consisting of arc and ring reflexions. This was interpreted as suggesting an ordered arrangement of cristae, in the mitochondria from these muscles.

X-ray diffraction from Al powder using energy dispersive technique

Using the energy dispersive x ...ray diffraction (EDXD) technique, the room temperature diffraction pattern of Al powder was obtained at diffraction angles ~ 30° and 50°. From the small angle diffraction pattern the average relative intensities (IR) of the (111), (200), and (220) lines were measured to be equal to 100, 62, and 32 respectively. From the large diffraction angle IR for the (220), (311+222), (400), (331+420), and (422) lines were measured to be 100,201,17,90, and 19.5 respectively. The diffraction pattern at those two angles were obtained at several higher temperatures to measure the change in the intensities of the Al lines. From the intensity changes the increase of the Debye- Waller temperature factor, i.e ~B(T), with respect to the value at room temperature was determined to be 0.6+0.1 at 250°C, 1.10+0.15 at 350°C, 1.45+0.20 at 450°C, and 2.20±0.35 at 550°C.

Electronic, magnetic and thermal properties of Pb₂₋x AxCrO₅ (A = K or La)

Lead chromium oxide is a photoconductive dielectric material tha t has great potential of being used as a room temperature photodetector. In this research, we made ceramic pellets of this compound as well as potassium doped compound Pb2-xKxCr05, where x=O, 0.05, 0.125. We also investigate the properties of the lanthanum doped sample whose chemical formula is Pb1.85Lao.15Cr05' The electronic, magnetic and thermal properties of these materials have been studied. Magnetization measurements of the Pb2Cr05 sample indicate a transition at about 310 K, while for the lanthanum doped sample the transition temperature is at about 295 K indicating a paramagnetic behavior. However, the potassium doped samples are showing the transition from paramagnetic state to diamagnetic state at different temperatures for different amounts of potassium atoms present in the sample. We have studied resistivity as a function of temperature in different gas environments from 300 K to 900 K. The resistivity measurement of the parent sample indicates a conducting to insulating transition at about 300 K and upon increasing the temperature further, above 450 K the sample becomes an ionic conductor. As temperature increases a decrease in resistance is observed in the lanthanum/potassium doped samples. Using Differential Scanning Calorimetry experiment an endothermic peak is observed for the Pb2Cr05 and lanthanum/potassium doped samples at about 285 K.

Patient-specific model of a scoliotic torso for surgical planning

A method for the construction of a patient-specific model of a scoliotic torso for surgical planning via inter- patient registration is presented. Magnetic Resonance Images (MRI) of a generic model are registered to surface topography (TP) and X-ray data of a test patient. A partial model is first obtained via thin-plate spline registration between TP and X-ray data of the test patient. The MRIs from the generic model are then fit into the test patient using articulated model registration between the vertebrae of the generic model’s MRIs in prone position and the test patient’s X-rays in standing position. A non-rigid deformation of the soft tissues is performed using a modified thin-plate spline constrained to maintain bone rigidity and to fit in the space between the vertebrae and the surface of the torso. Results show average Dice values of 0.975 ± 0.012 between the MRIs following inter-patient registration and the surface topography of the test patient, which is comparable to the average value of 0.976 ± 0.009 previously obtained following intra-patient registration. The results also show a significant improvement compared to rigid inter-patient registration. Future work includes validating the method on a larger cohort of patients and incorporating soft tissue stiffness constraints. The method developed can be used to obtain a geometric model of a patient including bone structures, soft tissues and the surface of the torso which can be incorporated in a surgical simulator in order to better predict the outcome of scoliosis surgery, even if MRI data cannot be acquired for the patient.

Multimodal image registration of the scoliotic torso for surgical planning

Background This paper presents a method that registers MRIs acquired in prone position, with surface topography (TP) and X-ray reconstructions acquired in standing position, in order to obtain a 3D representation of a human torso incorporating the external surface, bone structures, and soft tissues. Methods TP and X-ray data are registered using landmarks. Bone structures are used to register each MRI slice using an articulated model, and the soft tissue is confined to the volume delimited by the trunk and bone surfaces using a constrained thin-plate spline. Results The method is tested on 3 pre-surgical patients with scoliosis and shows a significant improvement, qualitatively and using the Dice similarity coefficient, in fitting the MRI into the standing patient model when compared to rigid and articulated model registration. The determinant of the Jacobian of the registration deformation shows higher variations in the deformation in areas closer to the surface of the torso. Conclusions The novel, resulting 3D full torso model can provide a more complete representation of patient geometry to be incorporated in surgical simulators under development that aim at predicting the effect of scoliosis surgery on the external appearance of the patient’s torso.