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.Tue, 19 Jan 2021 19:28:44 GMT2021-01-19T19:28:44Z10291Scattering in two targets with the vector code MCSHAPEhttp://hdl.handle.net/11585/19159Titolo: Scattering in two targets with the vector code MCSHAPE
Abstract: Using the Monte Carlo code MCSHAPE, some simulations have been made by varying the angle between the scattering plane with the incident beam (defined by the incident beam and the beam 1) and the scattering plane of the collision with the second target (defined by beam 1 and the outgoing beam). The code MCSHAPE, in fact, can simulate the behaviour of arbitrarily polarised photons and can follow the evolution of their polarisation state after the interaction with the atoms. The polarisation state of the photons is described using the Stokes parameters I, Q, U and V, having the dimension of an intensity and containing all the physical information about the polarisation state. Simulated experiments with a monochromatic unpolarised source of 59,54 keV (main gamma line of 241Am) and with an x-ray tube source have been considered. In the first case, the results of the simulations show that, after the 90° scattering in the first target, a part of the scattered beam (beam 1) is polarised (the degree of polarisation is a function of energy, and as it is shown, for some energies, 90% of the beam is polarised), but it is not fully polarised as for the single scattering (this is an effect of the multiple scattering in the target).The intensity collected by the detector, after the scattering with the second target, depends on the rotation between the first and the second pieces of the tube. The scattering is drastically reduced for a rotation angle around 90°, even if, due to multiple scattering, it is not zero. This behaviour was tested also with polychromatic excitation.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11585/191592005-01-01T00:00:00ZVisualization of scattering angular distributions with the SAP codehttp://hdl.handle.net/11585/86659Titolo: Visualization of scattering angular distributions with the SAP code
Abstract: SAP (Scattering Angular distribution Plot) is a graphical tool developed at the University of Bologna to compute and plot Rayleigh and Compton differential cross-sections (atomic and electronic), form-factors (FFs) and incoherent scattering functions (SFs) for single elements, compounds and mixture of compounds, for monochromatic excitation in the range of 1–1000 keV. The computation of FFs and SFs may be performed in two ways: (a) by interpolating Hubbell’s data from EPDL97 library and (b) by using semi-empirical formulas as described in the text. Two kinds of normalization permit to compare the plots of different magnitudes, by imposing a similar scale. The characteristics of the code SAP are illustrated with one example.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/11585/866592010-01-01T00:00:00ZElectron contribution to photon transport in coupled photon-electron problems: inner-shell impact ionization correction to XRFhttp://hdl.handle.net/11585/185908Titolo: Electron contribution to photon transport in coupled photon-electron problems: inner-shell impact ionization correction to XRF
Abstract: The Monte Carlo code PENELOPE (coupled electron-photon Monte Carlo) has been used to compute the effect of the secondary electrons on the X-ray fluorescence characteristic lines. The mechanism that produces this contribution is the inner-shell impact ionization. The ad hoc code KERNEL (which calls the PENELOPE library) has been used to simulate a forced first collision at the origin of coordinates. The electron correction (produced by the secondary electrons and their multiple scattering) has been studied in terms of angle, space and energy. The energy dependence has been quantified in the interval 1-150keV, for all the emission lines (K, L and M) of the elements with atomic numbers Z=11-92. For each characteristic line, the energy dependence is described by simple parametric expressions corresponding to the five energy regions delimited by the K, L1, L2 and L3 absorption edges. It has been introduced a new photon kernel comprising the correction due to inner-shell impact ionization. The new kernel is suitable to be adopted in photon transport codes (either deterministic or Monte Carlo) with a minimal effort. Finally, the new kernel has been studied for different elements and lines to trace a general behavior.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11585/1859082013-01-01T00:00:00ZThe Monte Carlo code MCSHAPE: Main features and recent developmentshttp://hdl.handle.net/11585/486971Titolo: The Monte Carlo code MCSHAPE: Main features and recent developments
Abstract: MCSHAPE is a general purpose Monte Carlo code developed at the University of Bologna to simulate the diffusion of X- and gamma-ray photons with the special feature of describing the full evolution of the photon polarization state along the interactions with the target. The prevailing photon-matter interactions in the energy range 1–1000 keV, Compton and Rayleigh scattering and photoelectric effect, are considered. All the parameters that characterize the photon transport can be suitably defined: (i) the source intensity, (ii) its full polarization state as a function of energy, (iii) the number of collisions, and (iv) the energy interval and resolution of the simulation. It is possible to visualize the results for selected groups of interactions. MCSHAPE simulates the propagation in heterogeneous media of polarized photons (from synchrotron sources) or of partially polarized sources (from X-ray tubes). In this paper, the main features of MCSHAPE are illustrated with some examples and a comparison with experimental data.
The Monte Carlo code MCSHAPE: main features and recent developments. Available from: https://www.researchgate.net/publication/273261334_The_Monte_Carlo_code_MCSHAPE_main_features_and_recent_developments.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11585/4869712015-01-01T00:00:00ZEvaluation 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/11585/5188512015-01-01T00:00:00ZA modeling tool for detector resolution and incomplete charge collectionhttp://hdl.handle.net/11585/486768Titolo: A modeling tool for detector resolution and incomplete charge collection
Abstract: The detector response function of X-ray and gamma-ray detectors is obtained from the convolution of the energy deposition spectrum with the detector resolution function. The energy deposition spectrum can be computed by using deterministic or Monte Carlo codes, while the energy resolution depends specifically on the detection mechanism, which is characteristic of the single detector. In a first approximation, the energy resolution can be modeled using a normalized Gaussian distribution having its full width at half maximum expressed in terms of specific semiempirical formulas for solid-state detectors, scintillators, and gas proportional counters. However, this approach is not sufficient with some solid-state detectors. It is frequent to find that the peaks show a deviation from the Gaussian shape: a long flat shelf structure from the peak centroid to the lower energies and an asymmetry that can be described with an exponential decay on the left side of the peak. These two effects have been introduced in the new tool RESOLUTION by adapting empirical models found in literature. RESOLUTION can be tailored to the specific detector by analyzing measured monochromatic peaks by means of the following strategies: (1) in a first approximation, a Gaussian shape is assumed in order to determine the full width at half maximum parameters, (2) if it is noted a flat background on the left side of the peak, then a shelf function is added, and (3) if a departure of the Gaussian is observed, then an exponential tail function is added. RESOLUTION gives a very precise description of the line shape.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11585/4867682015-01-01T00:00:00ZReconstruction of the X-ray tube spectrum from a scattering measurementhttp://hdl.handle.net/11585/118204Titolo: Reconstruction of the X-ray tube spectrum from a scattering measurement
Abstract: An inverse technique has been designed to unfold the x-ray tube spectrum from the measurement of the photons scattered by a target interposed in the path of the beam.
A special strategy is necessary to circumvent the ill-conditioning of the forward transport algebraic problem.The proposed method is based on th ecalculation of both, the forward and adjoint analytical solutions of the Boltzmann transport equation.
After testing the method with numerical simulations, a simple prototype built at the Operational Unit of Health Physics of the University of Bologna was used to test the method experimentally.
The reconstructed spectrum was validated by comparison with a straightforward measurement of the X-ray beam. The influence of the detector was corrected in both cases using standard unfolding techniques.
The method is capable to accurately characterize the intensity distribution of an X-ray tube spectrum, even at low energies where other methods fail.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11585/1182042012-01-01T00:00:00ZImprovement 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/11585/4869742015-01-01T00:00:00ZScattering computation on two targets using the vector code MCSHAPEhttp://hdl.handle.net/11585/1453Titolo: Scattering computation on two targets using the vector code MCSHAPE
Abstract: Using the Monte Carlo code MCSHAPE, some simulations have been made by varying the angle between the scattering plane with the incident beam (defined by the incident beam and the beam 1) and the scattering plane of the collision with the second target (defined by beam 1 and the outgoing beam). The code MCSHAPE, in fact, can simulate the behaviour of arbitrarily polarised photons and can follow the evolution of their polarisation state after the interaction with the atoms. The polarisation state of the photons is described using the Stokes parameters I, Q, U and V, having the dimension of an intensity and containing all the physical information about the polarisation state. Simulated experiments with a monochromatic unpolarised source of 59,54 keV (main gamma line of 241Am) and with an x-ray tube source have been considered. In the first case, the results of the simulations show that, after the 90° scattering in the first target, a part of the scattered beam (beam 1) is polarised (the degree of polarisation is a function of energy, and as it is shown, for some energies, 90% of the beam is polarised), but it is not fully polarised as for the single scattering (this is an effect of the multiple scattering in the target).The intensity collected by the detector, after the scattering with the second target, depends on the rotation between the first and the second pieces of the tube. The scattering is drastically reduced for a rotation angle around 90°, even if, due to multiple scattering, it is not zero.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11585/14532004-01-01T00:00:00ZDeterministic and Monte Carlo codes for multiple scattering
photon transporthttp://hdl.handle.net/11585/110425Titolo: Deterministic and Monte Carlo codes for multiple scattering
photon transport
Abstract: Deterministic and Monte Carlo techniques compete to provide the best description of transport problems. This article presents three examples from our experience in photon transport, which illustrate the close complementarity of these two approaches.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11585/1104252012-01-01T00:00:00Z