Jorge Eduardo Fernandez | Università di Bologna (original) (raw)

Books by Jorge Eduardo Fernandez

European Conference on Energy Dispersive X-Ray Spectrometry (EDXRS-98) Book of Abstracts, Jun 1998

Special Issues by Jorge Eduardo Fernandez

Radiation Physics and Chemistry, 2019

Radiation Physics and Chemistry, 2009

5th Topical Meeting on Industrial Radiation and Radioisotope Measurement Applications (IRRMA-V), Jan 2004

Book Chapters by Jorge Eduardo Fernandez

ABSTRACT It is well known that the polarisation state of the source radiation influences the beha... more ABSTRACT It is well known that the polarisation state of the source radiation influences the behaviour of the photons in their interaction with the matter. The most important phenomena in the energy range of x-rays, photoelectric effect, coherent (or Rayleigh) scattering and incoherent (or Compton) scattering, are differently influenced by such a polarisation state. Photoelectric effect does not feel the effect of the polarisation and has an isotropic cross-section. Rayleigh and Compton scattering instead, are strongly influenced by both, the polarisation state and the scattering geometry. In particular, when a linearly polarised beam, whose electric field is parallel to the scattering plane, scatters at 90 degrees, both Rayleigh and Compton scattering tend to vanish for a single scattering. In fact, this paradigmatic behaviour allows us to eliminate the ‘noise’ due to scattering and to collect only the signal produced by the photoelectric effect. These phenomena are more complex in the presence of the multiple scattering: for the same geometry, the total scattering is no longer zero even if it remains considerably reduced. In order to study this phenomenon, the following configuration is proposed. (figure) Using the Monte Carlo code MCSHAPE [1], 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 it follows the evolution of their polarisation state after the interaction with the atoms. The polarisation state of the photons is described, in the code, thanks to 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 241-Am) 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 is tested also with polychromatic excitation. An experimental apparatus is being developed in order to investigate in detail the rotational dependence of this configuration. [1] J.E. Fernandez, V.G. Molinari, M. Bastiano and V. Scot. Diffusion of photons with arbitrary state of polarisation: the Monte Carlo code MCSHAPE. Nuclear Instruments and Methods B 213 (2004) 105-107 (see also http://shape.ing.unibo.it)

In Advanced Monte Carlo Computer Programs for Radiation Transport (OECD Documents 6695011), 1995

X-Ray Spectrometry, 2005

In x-ray fluorescence spectroscopy, a photon beam is focused on the sample to stimulate the emiss... more In x-ray fluorescence spectroscopy, a photon beam is focused on the sample to stimulate the emission of characteristic radiation. Even if a qualitative interpretation of the measurements is simple, a quantitative analysis is not straightforward because the primary photons are produced deep in the target and the properties of the radiation that reaches the detector are modified significantly by the interactions undergone before leaving the specimen. Understanding how the emission spectra are influenced by interactions with matter is a central problem in fluorescence analysis. In this work, by using the 3D transport equation, we found that not only the composition of the specimen but also the geometry of the system plays an important role in determining the properties of the radiation field, denoting by geometry the shape of the target, the direction of the incoming beam and the observation angle.

X-Ray and Neutron Capillary Optics II, Muradin A. Kumakhov; Richard B. Hoover Eds., Dec 6, 2006

ABSTRACT The vector equation is the best model known for describing the diffusion of incoherent p... more ABSTRACT The vector equation is the best model known for describing the diffusion of incoherent photon beams. In this article, a brief overview of the Boltzmann transport equation (scalar and vector) will be given. Then, it will be described the state-of-the-art of the transport codes we developed at Bologna based on this model. Finally, the application of the codes will be illustrated with some examples.

In book: Microscopical X-Ray Fluorescence Analysis, 2000

Proceedings of the European Conference on Energy Dispersive X-Ray Spectrometry 1998 (EDXRS-98)

In this paper the 3D photon transport equation is considered to give a detailed description of t... more In this paper the 3D photon transport equation is considered to give a detailed description of the fluorescence photon emission from a homogeneous slab. As an example we study, with a complete 3D spatial description in plane geometry, the distribution both in physical and momentum space of the primary photons, induced by a radiation beam crossing the slab. Then we will see how the 3D geometry influences the shape of the continuous spectra due to a second Compton collision which modifies the distribution of the primaries due to photoelectric effect. The possibility of isolating the effect of a particular interaction is one of the strength points of the multiple-scattering scheme in the framework of transport techniques, which allows a better understanding of the photon diffusion. In order to evaluate the effects of the boundary conditions, we will use the integral transport equation instead of the integro-differential one, which has the advantage of treating the flow of the photons from the outer space as an external source. The results will be compared with those obtained in the case of a half-infinite medium uniformly irradiated with a plane infinite slant source of monochromatic photons previously solved in 1D.

European Conference on Energy Dispersive X-Ray Spectrometry (EDXRS-98) Book of Abstracts, Jun 1998

Radiation Physics and Chemistry, 2019

Radiation Physics and Chemistry, 2009

5th Topical Meeting on Industrial Radiation and Radioisotope Measurement Applications (IRRMA-V), Jan 2004

ABSTRACT It is well known that the polarisation state of the source radiation influences the beha... more ABSTRACT It is well known that the polarisation state of the source radiation influences the behaviour of the photons in their interaction with the matter. The most important phenomena in the energy range of x-rays, photoelectric effect, coherent (or Rayleigh) scattering and incoherent (or Compton) scattering, are differently influenced by such a polarisation state. Photoelectric effect does not feel the effect of the polarisation and has an isotropic cross-section. Rayleigh and Compton scattering instead, are strongly influenced by both, the polarisation state and the scattering geometry. In particular, when a linearly polarised beam, whose electric field is parallel to the scattering plane, scatters at 90 degrees, both Rayleigh and Compton scattering tend to vanish for a single scattering. In fact, this paradigmatic behaviour allows us to eliminate the ‘noise’ due to scattering and to collect only the signal produced by the photoelectric effect. These phenomena are more complex in the presence of the multiple scattering: for the same geometry, the total scattering is no longer zero even if it remains considerably reduced. In order to study this phenomenon, the following configuration is proposed. (figure) Using the Monte Carlo code MCSHAPE [1], 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 it follows the evolution of their polarisation state after the interaction with the atoms. The polarisation state of the photons is described, in the code, thanks to 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 241-Am) 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 is tested also with polychromatic excitation. An experimental apparatus is being developed in order to investigate in detail the rotational dependence of this configuration. [1] J.E. Fernandez, V.G. Molinari, M. Bastiano and V. Scot. Diffusion of photons with arbitrary state of polarisation: the Monte Carlo code MCSHAPE. Nuclear Instruments and Methods B 213 (2004) 105-107 (see also http://shape.ing.unibo.it)

In Advanced Monte Carlo Computer Programs for Radiation Transport (OECD Documents 6695011), 1995

X-Ray Spectrometry, 2005

In x-ray fluorescence spectroscopy, a photon beam is focused on the sample to stimulate the emiss... more In x-ray fluorescence spectroscopy, a photon beam is focused on the sample to stimulate the emission of characteristic radiation. Even if a qualitative interpretation of the measurements is simple, a quantitative analysis is not straightforward because the primary photons are produced deep in the target and the properties of the radiation that reaches the detector are modified significantly by the interactions undergone before leaving the specimen. Understanding how the emission spectra are influenced by interactions with matter is a central problem in fluorescence analysis. In this work, by using the 3D transport equation, we found that not only the composition of the specimen but also the geometry of the system plays an important role in determining the properties of the radiation field, denoting by geometry the shape of the target, the direction of the incoming beam and the observation angle.

X-Ray and Neutron Capillary Optics II, Muradin A. Kumakhov; Richard B. Hoover Eds., Dec 6, 2006

ABSTRACT The vector equation is the best model known for describing the diffusion of incoherent p... more ABSTRACT The vector equation is the best model known for describing the diffusion of incoherent photon beams. In this article, a brief overview of the Boltzmann transport equation (scalar and vector) will be given. Then, it will be described the state-of-the-art of the transport codes we developed at Bologna based on this model. Finally, the application of the codes will be illustrated with some examples.

In book: Microscopical X-Ray Fluorescence Analysis, 2000

Proceedings of the European Conference on Energy Dispersive X-Ray Spectrometry 1998 (EDXRS-98)

In this paper the 3D photon transport equation is considered to give a detailed description of t... more In this paper the 3D photon transport equation is considered to give a detailed description of the fluorescence photon emission from a homogeneous slab. As an example we study, with a complete 3D spatial description in plane geometry, the distribution both in physical and momentum space of the primary photons, induced by a radiation beam crossing the slab. Then we will see how the 3D geometry influences the shape of the continuous spectra due to a second Compton collision which modifies the distribution of the primaries due to photoelectric effect. The possibility of isolating the effect of a particular interaction is one of the strength points of the multiple-scattering scheme in the framework of transport techniques, which allows a better understanding of the photon diffusion. In order to evaluate the effects of the boundary conditions, we will use the integral transport equation instead of the integro-differential one, which has the advantage of treating the flow of the photons from the outer space as an external source. The results will be compared with those obtained in the case of a half-infinite medium uniformly irradiated with a plane infinite slant source of monochromatic photons previously solved in 1D.

Advances in X-Ray Analysis, 1992

Advances in X-Ray Analysis, 1992

Advances in X-Ray Analysis, 1992

Advances in Nuclear Science and Technology Vol. 22

X-ray photons - as many other particles - interact with matter producing secondary radiation that... more X-ray photons - as many other particles - interact with matter producing secondary radiation that carries useful information about the atoms comprising the target. The availability of intense sources of highly monochromatic X-rays and the great improvement in detector technology intensified research in X-ray spectrometry in the last twenty years. New techniques allowed the attenuation coefficients and the physics of the atom to be better known: Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Near Edge Structure (XANES), and Inelastic X-ray Scattering Spectroscopy (IXSS). Old techniques, like X-ray Fluorescence (XRF), gained in precision thus extending the horizon of applicability to new elements and energy ranges, and consequently Energy Dispersive X-ray Fluorescence (EDXRF) and Synchrotron Radiation X-ray Fluorescence (SRXRF) were evolved. Particle induced X-ray emission spectroscopy also benefited from this improvement. The field of application of X-ray spectrometry has grown from atomic, to nuclear, to plasma physics, to astrophysics. In this work the authors summarize the knowledge recently gained about how the intensity due to multiple scattering perturbs the first-order terms of the three processes of main interest in X-ray spectrometry between 1 keV and 100 keV: the photoelectric, the Rayleigh and the Compton effects. They show that the contribution of a few orders of scattering, calculated in the frame of transport theory, allows the construction of a theoretical X-ray spectrum that matches well experimental data from targets of homogeneous composition and infinite thickness. 99 refs., 15 figs.

Advances in X-Ray Analysis, 1990

Advances in X-Ray Analysis, 1990

Advances in X-Ray Analysis

X-Ray Spectrometry, 2007

... 0 di⊳x⊲ dx dx REFERENCES 1. Gardner RP, Ely RL Jr. Radioisotope Measurement Applications In E... more ... 0 di⊳x⊲ dx dx REFERENCES 1. Gardner RP, Ely RL Jr. Radioisotope Measurement Applications In Engineering. Reinhold Publishing Corporation: New York, 1967. 2. Duke PR, Hanson JA.Compton scatter densitometry with polychromatic sources. Med. Phys. 1984; 11: 624. ...

Radiation Physics and Chemistry, 2001

Radiation Physics and Chemistry, 2001

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1992

Radiation Physics and Chemistry, 2009

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1993

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1989

Journal of Physics B: Atomic, Molecular and Optical Physics, 2003

Applied Radiation and Isotopes, 1995

Applied Radiation and Isotopes, 2012

Journal of Physics B: Atomic, Molecular and Optical Physics, 2003

The Compton effect is a potential ionization mechanism of atoms. It produces vacancies in inner s... more The Compton effect is a potential ionization mechanism of atoms. It produces vacancies in inner shells that are filled with the same mechanism of atomic relaxation as the one following photo-absorption. This contribution to X-ray fluorescence emission is frequently neglected because the total Compton cross-section is apparently much lower than the photoelectric one at useful X-ray energies. However, a more careful analysis suggests that is necessary to consider single shell cross sections (instead of total cross sections) as a function of energy. In this article these Compton cross sections are computed for the shells K, L1-L3 and M1-M5 in the framework of the impulse approximation. By comparing the Compton and the photoelectric cross-section for each shell it is then possible to determine the extent of the Compton correction to the intensity of the corresponding characteristic lines. It is shown that for the K shell the correction becomes relevant for excitation energies which are too high to be considered in X-ray spectrometry. In contrast, for L and M shells the Compton contribution is relevant for medium-Z elements and medium energies. To illustrate the different grades of relevance of the correction, for each ionized shell, the energies for which the Compton contribution reaches the extent levels of 1, 5, 10, 20, 50 and 100% of the photoelectric one are determined for all the elements with Z = 11–92. For practical applications it is provided a simple formula and fitting coefficients to compute average correction levels for the shells considered.

X-Ray Spectrometry, 2015

Secondary electrons produced by Compton scattering and photoelectric effect contribute to the pho... more 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.