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Innovative approaches for Monte Carlo simulations of orientational effects in crystals and their experimental verification
Full text linkInteraction of either charged or neutral particles with crystals is an area of
science under development. Coherent effects of ultra‐relativistic particles in
crystals allow manipulating particle trajectories thanks to the strong electrical
field generated between atomic planes and axes. Coherent effects for interaction
of particles with aligned structures always exploited opportunity furnished by
the most advanced calculators and calculation methods of the current period.
In this thesis two Monte Carlo codes were developed for the simulation of
coherent interactions between charged particles and crystals. The Monte Carlo
codes were tested for comparison with the experimental results of various
experiments on channeling and related topics. The first code, named
DYNECHARM++, is completely object‐oriented and deals with numerical
integration of the equation of motion to determine the trajectory of a particle in
straight and bent complex crystalline structures. The second code addresses the
implementation of coherent effects, such as planar channeling and volume
reflection to Geant4, which is a widespread used toolkit for the simulation of the
passage of particles through matter. Experiments on coherent interactions were
carried out at the H8 and H4 external lines of the SPS at CERN and at the MAMI of
the Johannes Gutenberg University of Mainz. At the H8 line experiments of
coherent interaction in "exotic" atomic structure and crystal configuration were
worked out. Within the UA9 experiment, a procedure for the on‐beam
characterization of the strips for the SPS crystal collimation experiment was
developed at the H8 line. At the H4 line and at MAMI the interaction of negative
particles with bent crystals was studie
Simulation of orientational effects in crystals with structural defects through DYNECHARM++
No full textThe presence of defects in a crystal modifies the displacement of the atoms and, thereby, the physical processes inside it, e.g., the orientational effects of ultra-relativistic particles. For channeled particles, the probability to undergo dechanneling, i.e., to leave the channeling state, may rise up because of the presence of linear dislocations, while the deflection efficiency for volume reflection is very much the same as for a perfect bent crystal. On the contrary, point defects do not affect the channeling efficiency unless very high volumetric concentration of defects is present. In order to simulate the influence of the defects on channeling and volume reflection, a routine has been specifically developed for the DYNECHARM++ toolkit
DYNECHARM++: a toolkit to simulate coherent interactions of high-energy charged particles in complex structures
No full textA toolkit for the simulation of coherent interactions between high-energy charged particles and complex crystal structures, called DYNECHARM++ has been developed. The code has been written in C++ language taking advantage of this object-oriented programing method. The code is capable to evaluating the elec- trical characteristics of complex atomic structures and to simulate and track the particle trajectory within them. Calculation method of electrical characteristics based on their expansion in Fourier series has been adopted. Two different approaches to simulate the interaction have been adopted, relying on the full inte- gration of particle trajectories under the continuum potential approximation and on the definition of cross-sections of coherent processes. Finally, the code has proved to reproduce experimental results and to simulate interaction of charged particles with complex structures
DYNECHARM++: a Software to Simulate the Motion of Charged Particles in Complex Atomic Structures
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ECHARM - A software for calculation of physical quantities of interest in coherent interaction of relativistic particles with crystals
No full textWe present an analytical model to calculate the
physical quantities of interest experienced by relativistic
particles in their motion aligned with periodic complex
atomic structure. Classical physics equations and the
expansion of periodic functions as a Fourier series have
been used for the calculation. This method allows to
calculate the contribution from all the planes and axes
inside the crystal, in contrast to other simulation codes for
which the motion is evaluated only on nearest neighbors
atomic strings. Based on the calculation technique we
have developed the “ECHARM” program, which allows
to calculate one- and two- dimensional averaged physical
quantities of interest. The calculation holds for the main
axes of any orthorhombic and tetragonal structures and
for any orientation in the cubic structure. To underline the
capability of the program, complex structures such as
zeolites have been worked out. Based on the “ECHARM”
code, simulation of the relativistic particle motion within
complex structures has been developed. With this code it
is possible to simulate the motion in bent crystal to study
planar and axial channeling volume reflection
Calculation of the potential for interaction of particles with complex atomic structures
No full textWe present a method for calculation of the potential and related physical quantities experienced by a particle traversing an aligned periodic complex atomic structure. Classical physics equations and the expansion of periodic functions as a Fourier series have been used for the calculation. Based on this method, we have developed the ECHARM program, which calculates one- and two-dimensional averaged physical quantities of interest along the main axes of any orthorhombic and tetragonal structure. For the case of cubic symmetry, the calculation holds for any orientation. Complex structures such as zeolites have been worked out to show the capability of the program. © 2010 The American Physical Society
Exploiting Channeling of Charged Particles for the Enhancement of the Ni64->Cu64 Reaction Yield
No full textObjectives The production techniques of radioisotopes for medical purposes is a valuable and important field in nuclear medicine. In particular, the expensive cost of the prime materials for the production via cyclotron obliges the search for new solutions to enhance the production rate with minor upgrades of the current instrumentations.Methods Oriented ordered structure can modify particle trajectories inside a medium leading to a sensible variation of the interaction rate with atomic nuclei [1]. Under particular orientation of the target with respect t the incident beam (the anti-channeling condition), the probability of inelastic interaction with nuclei can be enhanced up to two times with respect to the standard rate, leading to the increasing of the radioisotope production yield.Results The usage of a extensively tested Monte Carlo simulation tool allowed to demonstrate the possibility to exploit a crystalline Ni64 target in order to observe the predicted enhancement. The experimental conditions of the interaction of a 16.5 MeV/c proton beam with the target in the nozzle of an available commercial cyclotron were reproduced by means of the Geant4 tool-kit [2]. The map of the Cu64 production yield as a function of the alignment of the beam with the crystalline target was simulated and the needed parameters to run the experiment are summarized.Conclusions The exploitation of channeling of charged particles is a viable way to enhance the production yield of radioisotopes. The the expected gain was estimated and the experimental condition defined
Manufacturing and Characterization of Ultra Thin and Bent Silicon Crystals for Studies of Coherent Interactions with Negatively Charged Particle Beams
No full textEfficient steering of GeV-energy negatively charged particle beams was demonstrated to be possible with a new generation of thin bent silicon crystals. Suitable crystals were produced at the Sensor Semiconductor Laboratory of Ferrara starting from Silicon On Insulator wafers, adopting proper revisitation of silicon micromachining techniques such as Low Pressure Chemical Vapor Deposition, photolithography and anisotropic chemical etching. Mechanical holders, which allow to properly bend the crystal and to reduce unwanted torsions, were employed. Crystallographic directions and crystal holder design were optimized in order to excite quasi-mosaic effect along (1 1 1) planes. Prior to exposing the crystal to particle beams, a full set of characterizations were performed. Infrared interferometry was used to measure crystal thickness with high accuracy. White-light interferometry was employed to characterize surface deformational state and its torsion. High-resolution X-rays diffraction was used to precisely measure crystal bending angle along the beam. Manufactured crystals were installed and tested at the MAMI MAinz MIcrotron to steer sub-GeV electrons, and at SLAC to deflect an electron beam in the 1 to 10 GeV energy range
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