1,721,129 research outputs found
A compact X-ray tomograph based on a CMOS flat panel
No full textComputed-assisted tomography is widely used in industrial non-destructive testing and in several research areas. A must of the tomographic equipment is often the speed of acquisition of the radiographs. When energy resolution is not a problem, an area detector can be used and a fast acquisition can be obtained. There are several kinds of area detectors, but if it is important to analyze relative large samples, the choice is restricted to some flat panels. In this paper, we describe a prototype of a tomographic equipment based on a CMOS area detector. This detector works at room temperature and permits to analyze samples as large as 10 cm with a spatial resolution of 50 μm. Preliminary results are reported her
X-ray energy spectrometry: Application in the study of the ion-exchange kinetics
No full textThe X-ray flourescence analysis induced by small radioisotopic sources has been employed for the study of the ion-exchange resins kinetics. The advantages offered by this technique over other commonly used methods are (a) variations in the concentration of ions in the resin-bead can be determined without sample taking; and (b) automatic measurements lasting a few seconds provide a check on process trends. The ions trapped in the resin-bead, in various zones of the column, can be expressed analytically, and the result is in good agreement with what can be deduced from a simplified model based on the hypothesis that the exchange process is controlled by diffusion of ions from solution to resin
Multielemental X-ray fluorescence analysis of natural water by using a preconcentration technique with ion exchange resins
No full textThe analysis of trace element in different kinds of waters is described, using a preconcentration technique on ion exchange loaded filter papers. The filters were analyzed employing an energy dispersive X-ray fluorescence system characterized by radioisotopic excitation sources and gas proportional or semiconductor detectors. The detection limits of the method were experimentally determined and the elemental levels in typical waters were measured
X-ray tomography using a CMOS area detector
No full textA flat panel based on CMOS technology represents a valid alternative to other kinds of flat panels and to ccd detectors for X-ray imaging. Although the spatial resolution of the ccd sensors is better than that of a CMOS sensor, the last has a larger sensitive-area and it can work at room temperature reaching a dynamic performance comparable to that of a cooled ccd sensor. Other kinds of flat panels, such as TFT screen are much more expensive and they have lower spatial resolution and higher noise than the CMOS detector.
In this paper, an application of the CMOS sensor to X-ray tomography is described. Preliminary results are reported and discussed
L X-RAY-FLUORESCENCE CROSS-SECTIONS AND INTENSITY RATIOS IN SOME HIGH-Z ELEMENTS EXCITED BY 23.62-KEV AND 24.68-KEV PHOTONS
No full textLl, Lalpha, Lbeta, and Lgamma x-ray fluorescence cross sections have been measured for the elements Pr, Ho, Yb, Au, and Pb using photon energies of 23.62 and 24.68 keV. Measurements have been performed using an x-ray tube with a secondary-exciter system as the excitation source. The secondary exciters of Cd and In were pure metals (> 99.9%). The x-ray tube with a secondary-target arrangement was used to obtain high intensity with a high degree of monochromatization. By using an x-ray tube, it is possible to measure x-ray fluorescence cross sections and ratios even for low-intensity x rays (Ll). Experimental results have been compared with the theoretically calculated values of L x-ray fluoresence cross sections. A fairly good correspondence is observed between experimental and calculated values. The intensity ratios for the intense transitions I(Lbeta)/I(Lalpha) are in good agreement with the calculated values
COHERENT AND INCOHERENT-SCATTERING OF 42.75 AND 47.24 KEV X-RAY PHOTONS SCATTERED FROM AL, CU, Y, MO, AU AND PB
No full textUsing nearly monoenergetic unpolarized K alpha x-ray photons, measurements were made of the coherent and Compton scattered intensity in the atomic region 13 less than or equal to Z less than or equal to 82 at an angle of 90 degrees with a high-resolution Si(Li) detection system. In order to improve the efficiency of the detection system, the excitation source, detector and the sample assembly were placed in a vacuum chamber and a pressure of 10(-2) mbar was maintained throughout the measurements. Experimental scattering cross-sections are compared with the normalized integrated cross-sections based on form factor and incoherent scattering functions, Experimental coherent scattering cross-sections are higher than the theoretical values, indicating the resonance behaviour, fine structure effects and oscillation of coherent intensity around the absorption edges. Experimental incoherent scattering cross-sections are lower than the theoretical estimates for heavy elements, indicating the effect of electron binding at low photon energies
Thermoelectrically cooled semiconductor detectors for non-destructive analysis of works of art by means of Energy Dispersive X Ray Fluorescence
No full textThermoelectrically cooled semiconductor detectors, such as SI-PIN, Si-drift, Cd1-xZnxTe and HgI2, coupled to miniaturized low-power X-ray tubes, are well suited in portable systems for energy-dispersive X-ray fluorescence (EDXRF), analysis of archaeological samples. The Si-PIN detector is characterized by a thickness of about 300 mu m, an area of about 2 x 3 mm(2), an energy resolution of about 200-250 eV at 5.9 keV and an entrance window of 25 - 75 mu m. The Si-drift detector has approximately the same area and thickness, but an energy resolution of 155 eV at 5.9 keV. The efficiency of these detectors is around 100% from 4 to 10 keV, and then decreases versus energy, reaching similar to 9% at 30 keV. Coupled to a miniaturized 10 kV, 0.1 mA, Ca-anode or to a miniaturized 30 kV, 0.1 mA, W-anode X-ray tubes, portable systems can be constructed, which are able to analyse K-lines of elements up to about silver, and L-lines of heavy elements. The Cd1-xZnxTe detector has an area of 4 mm(2) and a thickness of 3 mm. It has an energy resolution of about 300 eV at 5.9 keV, and an efficiency of 100% over the whole range of X-rays. Finally the HgI2 detector has an efficiency of about 100% in the whole range of X-rays, and an energy resolution of about 200 eV at 5.9 keV. Coupled to a small 50-60 kV, 1 mA, W-anode X-ray tube, portable systems can be constructed, for the analysis of practically all elements. These systems were applied to analysis in the field of archaeometry and in all applications for which portable systems are needed or at least useful (for example X-ray transmission measurements, X-ray microtomography and so on). Results of in-field use of these detectors and a comparison among these room temperature detectors in relation to concrete applications are presented. More specifically, concerning EDXRF analysis, ancient gold samples were analysed in Rome, in Mexico City and in Milan, ancient bronzes in Sassari, in Bologna, in Chieti and in Naples, and sulfur (due to pollution) in an old roman fresco in the church of S. Stefano Rotondo (Rome)
Determination of red cell survival in rabbits by fluorescent axcitation analysis of stable rubidium
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L-X-RAY FLUORESCENCE CROSS-SECTIONS IN THE ATOMIC REGION 46-LESS-THAN-Z-LESS-THAN-51 EXCITED BY 6.47, 7.57 AND 8.12 KEV PHOTONS
No full textTotal L X-ray fluorescence cross sections have been measured for the elements Sb, Sn, In, Cd, Ag and Pd excited by 6.47, 7.57 and 8.12 keV photons. The measurements have been performed using an X-ray tube with a modified secondary exciter system as the excitation source. In order to improve the efficiency of the detection system, the excitation source, detector and the target assembly were placed in a vacuum chamber. The measurements were made at a pressure of 10(-2) mbar. The present system considerably reduces the scattering and background effects and improves the monochromaticity. The experimental results have been compared with the theoretical values evaluated using L-subshell fluorescence yields (omega(i)) and Coster-Kronig transition probabilities (f(ij)) based on relativistic Dirac-Hartree-Slater (RDHS) theory. It is observed that the L X-ray cross-section values for the elements in the region are in good agreement with the theoretical values based on RDHS theory. The average L-shell fluorescence yields have also been computed using the experimentally measured cross-section values and the theoretical photoionization cross sections. The average fluorescence yields have been compared with the available results in the literature
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