IRIS Università degli Studi di Bolognahttps://cris.unibo.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Wed, 23 Jun 2021 00:28:47 GMT2021-06-23T00:28:47Z1061Spectrum unfolding in X-ray spectrometry using the maximum entropy methodhttp://hdl.handle.net/11585/227278Titolo: Spectrum unfolding in X-ray spectrometry using the maximum entropy method
Abstract: The solution of the unfolding problem is an ever-present issue in X-ray spectrometry. The maximum entropy technique solves this problem by taking advantage of some known a priori physical information and by ensuring an outcome with only positive values. This method is implemented in MAXED (MAXimum Entropy Deconvolution), a software code contained in the package UMG (Unfolding with MAXED and GRAVEL) developed at PTB and distributed by NEA Data Bank. This package contains also the code GRAVEL (used to estimate the precision of the solution). This article introduces the new code UMESTRAT (Unfolding Maximum Entropy STRATegy) which applies a semi-automatic strategy to solve the unfolding problem by using a suitable combination of MAXED and GRAVEL for applications in X-ray spectrometry. Some examples of the use of UMESTRAT are shown, demonstrating its capability to remove detector artifacts from the measured spectrum consistently with the model used for the detector response function (DRF).
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11585/2272782014-01-01T00:00:00ZEvaluation of bremsstrahlung contribution to photon transport in coupled photon-electron problemshttp://hdl.handle.net/11585/518851Titolo: Evaluation of bremsstrahlung contribution to photon transport in coupled photon-electron problems
Abstract: The most accurate description of the radiation field in x-ray spectrometry requires the modeling of coupled photon–electron transport. Compton scattering and the photoelectric effect actually produce electrons as secondary particles which contribute to the photon field through conversion mechanisms like bremsstrahlung (which produces a continuous photon energy spectrum) and inner-shell impact ionization (ISII) (which gives characteristic lines). The solution of the coupled problem is time consuming because the electrons interact continuously and therefore, the number of electron collisions to be considered is always very high. This complex problem is frequently simplified by neglecting the contributions of the secondary electrons. Recent works (Fernández et al., 2013 and Fernández et al., 2014) have shown the possibility to include a separately computed coupled photon–electron contribution like ISII in a photon calculation for improving such a crude approximation while preserving the speed of the pure photon transport model. By means of a similar approach and the Monte Carlo code PENELOPE (coupled photon–electron Monte Carlo), the bremsstrahlung contribution is characterized in this work. The angular distribution of the photons due to bremsstrahlung can be safely considered as isotropic, with the point of emission located at the same place of the photon collision. A new photon kernel describing the bremsstrahlung contribution is introduced: it can be included in photon transport codes (deterministic or Monte Carlo) with a minimal effort. A data library to describe the energy dependence of the bremsstrahlung emission has been generated for all elements Z=1–92 in the energy range 1–150 keV. The bremsstrahlung energy distribution for an arbitrary energy is obtained by interpolating in the database. A comparison between a PENELOPE direct simulation and the interpolated distribution using the data base shows an almost perfect agreement. The use of the data base increases the calculation speed by several magnitude orders.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11585/5188512015-01-01T00:00:00ZBremsstrahlung contribution to the X-ray spectrum in coupled photon-electron transporthttp://hdl.handle.net/11585/486976Titolo: Bremsstrahlung contribution to the X-ray spectrum in coupled photon-electron transport
Abstract: Secondary electrons produced by Compton scattering and photoelectric effect contribute to the photon field through conversion mechanisms like bremsstrahlung and inner-shell impact ionization (ISII). Because electrons interact continuously, the solution of the coupled transport problem is complex and time consuming. For this reason, photon transport codes frequently neglect the effects due to secondary electrons. Both of these contributions have been computed by means of the ad hoc code KERNEL that uses the Monte Carlo code PENELOPE specific for coupled transport. The correction on the intensity of the characteristic lines due to ISII was treated in a recent paper of our group. This paper adds the continuous contribution to the radiation field due to bremsstrahlung by secondary electrons. The bremsstrahlung emission is studied in terms of angle, space, and energy. The continuous contribution is stored in a data library for selected photon source energies in the interval 1–150 keV and for all the elements Z = 1–92. For intermediate source energies, the single element contribution is obtained by interpolating the data library. An example is presented on how to use the data library to include bremsstrahlung in the simulation of a synchrotron experiment.
Bremsstrahlung contribution to the X-ray spectrum in coupled photon-electron transport: Bremsstrahlung contribution to the X-ray spectrum. Available from: https://www.researchgate.net/publication/275673925_Bremsstrahlung_contribution_to_the_X-ray_spectrum_in_coupled_photon-electron_transport_Bremsstrahlung_contribution_to_the_X-ray_spectrum.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11585/4869762015-01-01T00:00:00ZImprovement of the detector resolution in X-ray spectrometry by using the maximum entropy methodhttp://hdl.handle.net/11585/486974Titolo: Improvement of the detector resolution in X-ray spectrometry by using the maximum entropy method
Abstract: In every X-ray spectroscopy measurement the influence of the detection system causes loss of information. Different mechanisms contribute to form the so-called detector response function (DRF): the detector efficiency, the escape of photons as a consequence of photoelectric or scattering interactions, the spectrum smearing due to the energy resolution, and, in solid states detectors (SSD), the charge collection artifacts. To recover the original spectrum, it is necessary to remove the detector influence by solving the so-called inverse problem. The maximum entropy unfolding technique solves this problem by imposing a set of constraints, taking advantage of the known a priori information and preserving the positive-defined character of the X-ray spectrum. This method has been included in the tool UMESTRAT (Unfolding Maximum Entropy STRATegy), which adopts a semi-automatic strategy to solve the unfolding problem based on a suitable combination of the codes MAXED and GRAVEL, developed at PTB. In the past UMESTRAT proved the capability to resolve characteristic peaks which were revealed as overlapped by a Si SSD, giving good qualitative results. In order to obtain quantitative results, UMESTRAT has been modified to include the additional constraint of the total number of photons of the spectrum, which can be easily determined by inverting the diagonal efficiency matrix. The features of the improved code are illustrated with some examples of unfolding from three commonly used SSD like Si, Ge, and CdTe. The quantitative unfolding can be considered as a software improvement of the detector resolution.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11585/4869742015-01-01T00:00:00ZAngular distributions of scattering intensities with the SAP codehttp://hdl.handle.net/11585/102031Titolo: Angular distributions of scattering intensities with the SAP code
Abstract: Compton and Rayleigh scattering peak intensities and their ratio are used in reflection and transmission experiments to obtain information about the density of the investigated specimen. The ratio is preferred because it allows the reduction of the errors due to attenuation and geometry. In all cases it is fundamental to predict their angular distributions in order to design the optimal experiment for a given material. The code SAP (Scattering Angular distribution Plot) is a graphical tool to compute and plot Rayleigh and Compton differential cross-sections (atomic and electronic), form factors and incoherent scattering functions. In this work, the code is improved by adding the computation of Rayleigh and Compton first-order peak fluxes and intensities, and the Rayleigh-to-Compton peak ratio, in both, reflection and transmission geometries, for single elements, compounds and mixture of compounds, for monochromatic excitation in the range of 1–1000 keV. The new characteristics of the code are illustrated with some examples.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11585/1020312011-01-01T00:00:00ZContribution of inner shell Compton ionization to the X-ray fluorescence line intensityhttp://hdl.handle.net/11585/562443Titolo: Contribution of inner shell Compton ionization to the X-ray fluorescence line intensity
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/11585/5624432016-01-01T00:00:00Z