1,721,223 research outputs found
EDXRF procedure for quantitative analysis matching theoretically generated reference spectra to measured spectra
No full textThe diversity of processes that contribute to an x‐ray fluorescence spectrum make it difficult to obtain an accurate estimate of the line intensities needed to determine the sample composition in XRF analysis. The radiative contributions forming the spectrum are produced by the interactions that x‐ray photons undergo with the atoms of the sample. Many multiple scattering terms contribute to the continuous portions of spectrum that overlap the lines of interest. The lines themselves are formed by the overlap of many narrow (discrete) contributions and some continuous ones: one ‘primary intensity’ plus several enhancement terms. The lines can also interfere with other neighbouring lines produced in the sample. The resulting spectrum, sufficiently complicated at this stage, is still modified in a complex way by the influence of the detector response and successive digitalization by the multi‐channel analyser. The difficulties that such spectral complexity introduces in the process of extracting the ‘primary fluorescence intensity’ from the experimental spectrum can be overcome by using a theoretical spectrum of reference that, in this paper, was calculated using the code SHAPE. Such a theoretical spectrum has the property that all the single contributions are well known, and therefore can be used to estimate correctly the fraction of ‘primary fluorescence intensity’ under any experimental line of interest in the real spectrum enclosed between two given energy channels. Since the theoretical spectrum can be computed only for a known composition, the calculated fraction can be initially obtained by feeding SHAPE with an arbitrary composition. The fraction estimated with the theoretical spectrum is used to correct the corresponding peak area in the experimental measured spectrum, which in turn is used to obtain a new calculated composition. This result is used to feed a new spectrum computation, defining an iterative method that converges to the unknown composition. The theoretical details of this iterative method are described and some experimental examples of EDXRF analysis using this technique are given. The advantages of the method for treating some paradigmatic cases of analysis are also illustrated. Copyright © 1995 John Wiley & Sons, Ltd
Vector Monte Carlo for Simulation of Polarized Photons
No full textBased on a recent analytical solution of vector transport equations in plane geometry including polarization effects, a vector scheme for a Monte Carlo code was worked out. The new code, called MC-SHAPE, was developed both to emphasize the miscalculation in using the scalar approach with average polarization kernels and to extend results obtained with the analytical solution of the transport equation to higher orders of interaction. The code includes the Doppler broadening giving the momentum distribution due to electron pre-collision motion. To improve the comparison with analytical results, the code takes some feature from this model, which considers the scattering of a monochromatic and monodirectional collimated beam of x-rays on a semi-infinite and homogeneous target. Results of the evolution of the four components of the Stokes vector describing the back-scattered beam, are presented which allow the analysis of the complete polarization characteristics of the multiple scattering of Rayleigh and Compton effects. The good agreement found with both deterministic calculations and experimental data indicates the validity of the new code. ©1998 John Wiley & Sons, Ltd
A variance weighted regularization reconstruction of measured data in Compton scattering tomography
No full textApparecchiatura per la produzione endogena di radioisotopi, particolarmente per diagnostica tomografica ad emissione di positroni
No full textApparecchiatura per la produzione endogena di radioisotopi, particolarmente per diagnostica tomografica ad emissione di positoni, caratterizzata dal fatto di comprendere:
- una camera da vuoto, la cui superficie interna è trattata per resistere all'implantazione ionica,
- una coppia di elettrodi posti all'interno di detta camera da vuoto,
- un banco capacitivo,
- mezzi di connessione di detto banco capacitivo a detta coppia di elettrodi per la generazione tra questi di una scarica elettrica, che provoca la formazione di plasma e crea le condizioni per lo sviluppo di reazioni nucleari che generano radioisotopi,
- un'induttanza complessiva del circuito elettrico equivalente di detta apparecchiatura non superiore a 50nH,
- mezzi comunicanti con detta camera da vuoto per la creazione di un vuoto non superiore a 10-6 torr,
- mezzi comunicanti con detta camera da vuoto per l'immissione in essa, dopo la creazione del vuoto, di almeno un gas di reazione ad una pressione in grado di garantire la formazione di plasma durante la fase di scarica ed il raggiungimento di condizioni di confinamento di detto plasma dell'ordine di 1015 keV. sec/cm3, e
- mezzi comunicanti con detta camera da vuoto per l'estrazione di gas
Photon Scattering by Compounds: an assessment of the validity of the independent Atomic Model Approximation
No full textThe validity of the independent atomic model (IAM) for x-ray scattering, which assumes that each atom in the sample scatters independently of the others, was examined for materials and irradiation geometries where interatomic and intermolecular cooperative effects are expected to provide a non-negligible contribution. Samples of water, fat, polymers and powder were investigated by means of a simple powder diffractometer in the interval of momentum transfer 0.017 ≤ χ ≤ 0.67 {χ = E[sin(θ/2)]/12.4, E being the incident photon energy and θ the scattering angle}. Accurate evaluation of self-absorption, air scattering and other contamination was carried out by means of a Monte Carlo code. Simulation of the incident photon spectra permitted an assessment of non-monochromaticity effect. This allowed the accurate evaluation of the scattering intensities in terms of fundamental impact parameters. All the materials investigated showed marked discrepancies from the corresponding IAM theoretical results, even for intervals of momentum transfer in which this model is usually claimed to be valid. However, this work shows that the errors introduced by corrections are relatively low, making it possible to validate the use of simple diffractometry to evaluate the scattering factors in real samples without having to resort to sophisticated irradiation facilities
A Regularizatiom Method for Unfolding the Measured Data of Different X-Ray Spectrometers in Compton Scattering Tomography
No full textA Monte Carlo Code for Photon Transport for Plasam-Derived X-Ray Evaluation
No full textAbstract del volume: The problem of particle transport in extended systems is addressed in this book. It has important implications from both the conceptual and applied points of view. A community of researchers from different disciplines and fields is actively engaged in studying this problem, often using similar methodologies. The main subjects covered in this book are relevant to nonlinear diffusion in plasmas and to transport dynamics in accelerators and free electron lasers
New EDXRS exploitation of compton scattering properties
No full textThe exploitation of the information that can be obtained from the energy analysis of Compton‐scattered photons is discussed. It is shown that the use of the high‐energy wing part of this energy distribution adds a further tool for EDXRS analysis other than the evaluation of the total fluence area of the Compton (or incoherent) distribution and the total fluence area of the Rayleigh (or coherent) peak. Special attention is paid to those situations for which easy and unambiguous coherent peak evaluation is prevented. Copyright © 1995 John Wiley & Sons, Ltd
Multispectral Examination of Paintings: A Principal Component Image Analysis Approach
No full textNot availabl
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