This work presents the recent developments of xraylib, an ANSI C library designed to provide convenient access
to a large number of X-ray related databases, with a focus on quantitative XRF applications. The discussed
enhancements include improved XRF production cross sections that take into account cascade effects and M-lines,
as well as revised line energies, atomic level widths, Compton broadening profiles etc. A full overview is
presented of the complete API.
Performing computed assisted tomography (CAT) requires a perfect centering of the rotation axis with the center of the detector. This requirement is sometimes hard to obtain. Thus, a post acquisition centering correction of the acquired data is mandatory. Several correction techniques can be found in the literature. However, all of them are not completely reliable when the measure is not performed in perfect experimental condition. As matter of fact, researcher use to fit the center of rotation by a post measure visual inspection of the projections. This approach is not practical at high-throughput tomography system where hundreds of samples a day can be easily measured, moreover, the visual approach does not always give the best centering. In this paper we report a new centering technique that is more robust when the quality of the acquired data is poor due to low contrast or noisy acquisition.
Estimate of sorption of liquid materials inside porous stones and wood is an important parameter in industrial material testing and cultural heritage conservation. In the latter case, a suitable polymer can be used for both consolidation and conservation, it being applied either in the final form or as its parent monomer, which is subsequently allowed to polymerize in situ by the classical method or by frontal polymerization. In this paper a recently developed methodology based of X-ray tomography is presented. This technique has been applied to different types of wood and stone. The gradient of penetration has also been studied. Some of the results obtained are reported and discussed.
An image intensifier based computed tomography scanner and a tube source of x-rays are used to obtain the images of small objects, plastics, wood and soft materials in order to know the interior properties of the material. A new method is developed to estimate the degree of monochromacy, total solid angle, efficiency and geometrical effects of the measuring system and the way to produce monoenergetic radiation. The flux emitted by the x-ray tube is filtered using the appropriate filters at the chosen optimum energy and reasonable monochromacy is achieved and the images are acceptably distinct. Much attention has been focused on the imaging of small objects of weakly attenuating materials at optimum value. At optimum value it is possible to calculate the three-dimensional representation of inner and outer surfaces of the object. The image contrast between soft materials could be significantly enhanced by optimal selection of the energy of the x-rays by Monte Carlo methods. The imaging system is compact, reasonably economic, has a good contrast resolution, simple operation and routine availability and explores the use of optimizing tomography for various applications.
Transmission tomography is a powerful tool in several fields of investigation, ranging from medicine to industrial quality control. It is based on the radiation that doesn't interact with the sample and that reaches the detector. However, this kind of technique cannot always be used or the information from it is poor. In some of these cases other kinds of tomography can be applied such as scattering (Compton or Rayleigh) tomography or fluorescence tomography. The use of the latter techniques requires a different reconstruction technique of that used in transmission tomography. Some adaptation of the backprojection algorithm is often used, but in this case a complete scan of the sample is required with a fixed geometry. Another type of reconstruction algorithms are the iterative ones, but they present a high computational cost and so only small, low spatial resolution matrix, can be treated. In the past another kind of scanning techniques has been proposed. It is based on two linear translations (x-y) against translation and rotation required by the backprojection algorithm. The x-y scanning presents a big advantage compared with the backprojection scanning, i.e. the reconstruction does not need to be performed on the whole sample; it can also be performed on a part of the sample, the region of interest (ROI). However this scanning technique is affected by a big drawback: the influence of x-ray self-absorption by the matrix is stronger than the backprojection scanning producing a lower quality of the reconstruction. In this paper a recently developed correction technique is described.
A very simple and inexpensive CT-scanner has been designed and constructed, which is able to carry out contemporaneously transmission, Compton, Rayleigh and fluorescence radiation tomography. Four detectors are located around the object to be scanned: a NaI one at 180 degrees with respect to the incident radiation for transmission tomography; a second NaI at 90 degrees for Compton tomography; a third NaI at 5-10 degrees for Rayleigh tomography, and a Si-PIN or CdZnTe at 90 degrees for fluorescent radiation tomography. Special algorithms were employed, which include auto-absorption correction terms for Compton, Rayleigh and fluorescence tomography.
A critical point of several reconstruction and analysis algorithms in x-ray experiments is a fast simulation of the interaction of radiation with matter. This kind of simulation is usually based on Monte Carlo techniques, which follows each particle individual trajectory. Since the maximum number of interactions is a user-definable integer, Monte Carlo simulations allow to obtain an arbitrary precision. However, in several experiments the flux of photons that reach the detector after the interaction in the volume of interest (VOI) is very low, therefore the simulation time may be very large. Simple experiments of x- ray tomography may require several days to obtain reasonable statistics with the faster Monte Carlo codes. Particularly, in x-y scanning tomography both the detector and the x-ray tube are highly collimated. In such cases, conventional Monte Carlo techniques are inadequate. As a possible alternative, we propose an analytical spectrum generator, which evaluates the detected signal through the differential cross section for the single interaction with corrections for absorption of the beam (before the interaction point) and of the scattered photon (after the interaction point). It will be shown that the analytical projector proposed in this paper is several order faster than Monte Carlo based simulators.
Conventional algorithms for tomographic reconstruction require a discrete set of projections equally spaced over the full angular range of 180 degrees for a parallel beam or 180 degrees plus fan angle for a fan beam. A crucial point is the availability of a complete set of data. However, in some cases this requirement cannot be fulfilled. This happens, for example, in case of large objects, such as a pipeline or a wall, or when part of the projections was lost. In order to perform a reconstruction of the image from the partial set of projections, the data must be pre- processed. Several algorithms have been reported in literature, but the majority of them require a-priori knowledge of the shape and composition of the sample or they present a high computational cost. Recently a new algorithm has been proposed. It allows to recover the lacking projections without any a-priori assumption and with a relatively low computational cost. It is based on a morphing technique, which affords in general terms the problem of curve matching and has been specialized to the case of tomographic reconstruction. It has been applied to medical (transmission) tomography. In the present work such algorithm is applied to microtomographic measurements of different types (transmission, Compton and fluorescence tomography), which have been performed on industrial samples.
Compton scattering is a potential tool for the determination of bone mineral content or tissue density for dose planning purposes, and requires knowledge of the energy distribution of the X-rays through biological materials of medical interest in the X-ray and (gamma) -ray region. The energy distribution is utilized in a number of ways in diagnostic radiology, for example, in determining primary photon spectra, electron densities in separate volumes, and in tomography and imaging. The choice of the X-ray energy is more related to X-ray absorption, where as that of the scattering angle is more related to geometry. The evaluation of all the contributions are mandatory in Compton profile measurements and is important in X-ray imaging systems in order to achieve good results. In view of this, Compton profile cross-sections for few biological materials are estimated at nineteen K(alpha) X-ray energies and 60 keV (Am-241) photons. Energy broadening, geometrical broadening from 1 to 180 degree(s), FWHM of J(Pz) and FWHM of Compton energy broadening has been evaluated at various incident photon energies. These values are estimated around the centroid of the Compton profile with an energy interval of 0.1 keV and 1.0 keV for 60 keV photons. The interaction cross sections for the above materials are estimated using fractions-by-weight of the constituent elements. Input data for these tables are purely theoretical.
Elastic and inelastic scattering cross-sections for low, medium and high Z atoms are measured in vacuum using an x- ray tube with a secondary targets as an excitation source. Monoenergetic K(alpha) radiation emitted from the secondary target is used to excite the sample. Monoenergetic radiation emitted from the secondary target is used to excite the sample. Monoenergetic radiation is also produced using two secondary targets coupled to an x-ray tube and the radiation from the second target of the system is used to excite the sample. Elastic and inelastic scattering of K(alpha) X-ray line energies of the secondary target by the sample are recorded with Hp Ge and Si(Li) detectors. Using this system the degree of monochromaticity of the secondary emission and the geometrical effects of the measuring system is estimated. The efficiency is large because the secondary target acts as a converter. Experimental results based on this system will be presented and compared with theoretical estimates. The importance of the dat and the potential use of the system for few applications in the field of medicine and archaeometry will also be presented.
Images of small plastic and food materials are obtained using a tomographic device based on image intensifier at optimum energy. The flux emitted by the x-ray tube is filtered using appropriate filters at the chosen optimum energy and reasonable monochromacy is achieved and the images are acceptably distinct.
Various apparatus for x and (gamma) -ray computed tomography (CT) have been constructed by us during the last 20 years, with the aim of producing simple and low-cost systems for nondestructive testing. The first one was constructed in 1980 and used an Am241 radioactive source emitting 59.6 keV (gamma) -rays and a single NaI(Tl)-x ray detector. Successively, the radioactive source was substituted during the years by x-ray tubes, and the single detector by multi- detection system such as arrays of detectors and image intensifiers. The last CT-scanner employs a 160 kV x-ray tube and a 6' X 6' image intensifier coupled through a lens to a cooled CCD-camera. At the same time, also (gamma) CT-scanners were constructed for large size and/or high-density samples. These are based on Ir192 or Cs137 radioactive sources coupled to a single NaI(Tl)(gamma) -ray detector. The characteristics and properties of the CT-scanners based on the use of x-ray tubes, emitting x-rays in the energy range 20 - 100 keV, and on (gamma) emitting radioisotopes (Ir192 and Cs137) have been studied and will be described in this paper. Various types of objects have been studied: test objects and common objects such as tree trunks, wood fragments, nuts, ceramic samples, insulators and, etc. Samples have been imaged, after using iodine compounds as tracers.
Dedicated X-ray tubes and thermoelectrically cooled detectors have revolutionized in the last years the field of energy dispersive X-ray fluorescence (EDXRF) analysis. The small size of both X-ray tubes and detectors allowed the construction of portable systems, with characteristics similar to those of laboratory systems. The portability of the new EDXRF systems opened also all the new analytical fields where the 'sample' cannot be transported to the Laboratory (analysis of works of art in museum, analysis of minerals, of soil, and etc.).
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