German Tirao

An inelastic X-ray scattering spectrometer at LNLS

A high-resolution spectrometer aimed at performing experiments of inelastic X-ray scattering by electronic excitations is described. The spectrometer has been installed at the D12A-XRD1 beamline of the National Synchrotron Light Laboratory (LNLS), in Campinas, Brazil. Synchrotron radiation is monochromated to about 6 keV and focused horizontally onto the sample by a sagittally focusing Si(111) double-crystal monochromator in non-dispersive setting. The spectrometer operates in Rowland circle geometry and is based on a focusing Si(333) analyser in near-backdiffraction geometry for energy analysis of inelastically scattered photons. The analyser works at a fixed Bragg angle, so energy transfers are obtained by varying the incident photon energy. A relative energy resolution of the whole spectrometer of approximately 1.5 x 10(-4) at 5.93 keV has been achieved. As an example of application, inelastic X-ray scattering by plasmon excitation in polycrystalline Be was measured. Test results demonstrate that inelastic X-ray scattering experiments with eV energy resolution and an acceptable counting rate are feasible at the LNLS when focused on plasmon and particle-hole excitations.

Application of high resolution X-ray emission spectroscopy on the study of Cr ion adsorption by activated carbon.

In this work granular activated carbon has been chosen as an absorbent in order to investigate the Cr(VI) reduced by adsorption experiments. Several batch chromium-sorption experiments were carried out using 0.25 g of granular activated carbon in 50 mL aqueous solution containing approximately 70 and 140 mg L(-1) of Cr(VI) and Cr(III), respectively. Cr-Kbeta fluorescence spectra of Cr adsorbed in a carbon matrix and Cr reference materials were measured using a high-resolution Johann-type spectrometer. Based on evidence from the Cr-Kb satellite lines, the Cr(VI) reduction process has actually happened during metal adsorption by the activated carbon.

Plasmon excitation in beryllium: inelastic x-ray scattering experiments and first-principles calculations

An experimental and theoretical study of collective electronic excitations in Be is presented. The plasmon energy and linewidth were measured by means of inelastic x-ray scattering spectroscopy. Measurements were performed on a polycrystalline sample and in a broad range of momentum transfers within the plasmon excitation regime. Theoretical plasmon dispersion and its linewidth in the whole Brillouin zone were derived from ab initio evaluations of the electron density response function. The calculations were performed with full inclusion of the electron band structure within the random-phase approximation. Good agreement of experimental plasmon energy and linewidth dispersions with direction-averaged theoretical results in all investigated q-range is obtained. We conclude that, in Be, the band structure effects alone can account for the observed finite plasmon lifetime at q = 0, as well as for the linewidth dispersion in the long-wavelength domain.

Development and characterization of a microCT facility

This work reports the design, construction, characterization and application of a novel X-ray imaging beamline at Laboratorio de Investigación e Instrumentación en Física Aplicada a la Medicina e Imágenes por Rayos X - LIIFAMIRx - University of Cordoba and Institute of Physics E. Gaviola - CONICET, Argentina. This development is the first phase in the construction of the integral facility for combining different imaging modalities, like absorption contrast images by primary and scattering contributions, high-resolution micro-tomography, elastic scattering and X-ray fluorescence scanning for chemical composition and surface characterizations. The progress and results here reported concern mainly to the micro-tomography beam-line. This technique is already operative and it was used for several academic researches, application studies and services. The obtained results for the characterization of organic and inorganic samples demonstrated the feasibility and reliability of the developed facility. Accordingly, this work reports specific characteristics about its design, construction, and operation supporting its employment in a wide range of especial applications that might not be accomplished by other available techniques. Moreover, some application studies, mainly focused on biological samples, are presented.

Phylogenetic and functional implications of the ear region anatomy of Glossotherium robustum (Xenarthra, Mylodontidae) from the Late Pleistocene of Argentina

Several detailed studies of the external morphology of the ear region in extinct sloths have been published in the past few decades, and this anatomical region has proved extremely helpful in elucidating the phylogenetic relationships among the members of this mammalian clade. Few studies of the inner ear anatomy in these peculiar animals were conducted historically, but these are increasing in number in recent years, in both the extinct and extant representatives, due to wider access to CT-scanning facilities, which allow non-destructive access to internal morphologies. In the present study, we analyze the extinct ground sloth Glossotherium robustum and provide a description of the external features of the ear region and the endocranial side of the petrosal bone, coupled with the first data on the anatomy of the bony labyrinth. Some features observable in the ear region of G. robustum (e.g., the shape and size of the entotympanic bone and the morphology of the posteromedial surface of the petrosal) are highly variable, both intraspecifically and intraindividually. The form of the bony labyrinth of G. robustum is also described, providing the first data from this anatomical region for the family Mylodontidae. The anatomy of the bony labyrinth of the genus Glossotherium is here compared at the level of the superorder Xenarthra, including all available extant and extinct representatives, using geometric morphometric methods. In light of the new data, we discuss the evolution of inner ear anatomy in the xenarthran clade, and most particularly in sloths, considering the influence of phylogeny, allometry, and physiology on the shape of this highly informative region of the skull. These analyses show that the inner ear of Glossotherium more closely resembles that of the extant anteaters, and to a lesser extent those of the giant ground sloth Megatherium and euphractine armadillos, than those of the extant sloths Bradypus and Choloepus, further demonstrating the striking morphological convergence between the two extant sloth genera.

Digital Cranial Endocasts of the Extinct Sloth Glossotherium robustum (Xenarthra, Mylodontidae) from the Late Pleistocene of Argentina: Description and Comparison with the Extant Sloths

The internal cranial morphology of the terrestrial sloth Glossotherium robustum is described here based on a neurocranium from the late Pleistocene of the Pampean region of Buenos Aires, northeastern Argentina. The first published data on the morphology of the brain cavity of this species date back to the latest nineteenth century. The novel techniques of CT scanning and digital reconstructions enable non-destructive access to the internal cranial features of both extinct and extant vertebrates, and thus improve our knowledge of anatomical features that had previously remained obscure. Therefore, we performed CT scans on the posterior half of a skull of G. robustum and created digital models of the endocasts and internal structures. The results reveal the morphology of the brain cavity itself, as well as the paranasal sinuses and the trajectory of several cranial nerves and blood vessels. These features have been compared with the two extant folivoran genera, the two-toed sloth Choloepus and the three-toed sloth Bradypus. For many characteristics, especially those related to the paranasal pneumaticity and the brain cavity, a closer similarity between Glossotherium and Choloepus is observed, in accordance with the most widely accepted phylogenetic scenarios. However, other features are only shared by the two extant genera, but are probably related to allometric effects and the convergence that affected the two modern lineages. This study, which represents the first exhaustive analysis of digital endocasts of a fossil sloth, reveals the importance of the application of new methodologies, such as CT scans, for elucidating the evolutionary history of this peculiar mammalian clade.

Mammography image quality optimisation: a Monte Carlo study

Different irradiation configurations for typical mammographic facilities were evaluated in order to establish optimal irradiation parameters for improving X-ray image quality. The whole X-ray imaging process was suitably studied by means of Monte Carlo techniques. Relevant parameters were introduced to the program in order to evaluate their effect on image quality. Breast absorbed doses were presented as figure-of-merit with the aim of determining the optimal irradiation set-up with minimal dose delivery. It was found that anode material along with accelerating voltage significantly affected the image quality. On the other hand, micro-calcification detection was found to be strongly dependent on irradiation configurations as well as being affected by breast and micro-calcification compositions. Furthermore, by means of the adapted image processing algorithms, it was possible to quantitatively characterise the image quality as a function of different irradiation parameters. The proposed algorithms proved to be a useful, reliable and consistent tool for detail automatic detection.

A computational tool for evaluating the exposure risk in nuclear medicine treatments

A computational tool was developed with the aim of evaluating radiation exposure levels corresponding to patients and other exposed people, such as medical staff or chaperones, during typical nuclear medicine procedures. The calculation system is based on Monte Carlo subroutines adapted from the code PENELOPE and devoted to perform energy deposition according to the user-defined set-up. The computation tool offers a comfortable and user-friendly graphic interface for results processing and visualisation. Relevant procedure features, such as treatment room and facility, spatial distribution, source and target phantom as well as radioisotope type, can be easily introduced to the calculation code; this emphasises the versatility and potential of the computational tool. The application of the developed system to simple situations in nuclear medicine showed the reliability and feasibility of the proposed method. The obtained exposure risk maps proved to be useful to establish safe zones there where expositions do not exceed radioprotection tolerances.