Estudo da contribuição do espalhamento nuclear não elástico de prótons na dose depositada em alvos com composição homogênea

Due the differences between interaction physics process with matter for protons and photons, the proton beam tomography (pCT) has some vantages to comparison with conventional tomography. Also it is confirmed that usually pCT has better dose distribution and highest contrast resolution. The pCT allow not only view the internal structure of an object without destroying it, but also directly measure of volume density of electrons. Also it is confirmed that usually pCT has better dose distribution and highest contrast resolution. At the same time, there are many scientific and technical aspects to a detailed study: the capacity and limitations of the pCT methods are not well clarified. Through computations, based on Monte Carlo Method was carried out a detailed study of the contribution of non-elastic nuclear spreading, and together was compared with an analytical model for the deflection angle and the lateral deflection of protons in the target volume. The programs used were SRIM 2006 code and MCNPX v.2.50 code

Estudo teórico da contribuição a dose de partículas secundárias geradas por prótons de energias entre 100-200 MeV num phantom de músculo estriado

In the treatment plans in conventional Proton therapy are considered only the elastic interactions of protons with electrons and/or nuclei, it means, mainly ionization and coulomb excitation processes. As the energy needed to reach the deep tumors should be of several hundred of MeVs, certainly the nuclear inelastic channels are open. Only some previous studies of the contribution of these processes in the full dose have been made towards targets composed of water. In this study will be presented the results of the simulation of the processes of interaction of beams of protons in the range of 100-200 MeV of energy with a cylindrical phantom composed by striated muscle (ICRU), emphasizing in the contribution to total dose due to the deposition of energy by secondary particles alpha (α), deuterium (2H), tritium (3H), neutron (n) and hélio3 (3He), originated by nuclear inelastic processes. The simulations were performed by using the method of Monte Carlo, via the computer code MCNPX v2.50 (Monte Carlo N-Particle eXtended). The results will be shown demonstrated through the graphics of the deposited dose with or without nuclear interaction, the percentual of dose deposited by secondary particles, the radial dispersion of neutrons, as well as the multiplicity of secondary particles

Análise de algoritmos computacionais utilizados em sistemas de planejamento de braquiterapia de alta taxa de dose: estudo comparativo com o Código MCNP-5C

In radiotherapy, computational systems are used for radiation dose determination in the treatment’s volume and radiometric parameters quality analysis of equipment and field irradiated. Due to the increasing technological advancement, several research has been performed in brachytherapy for different computational algorithms development which may be incorporated to treatment planning systems, providing greater accuracy and confidence in the dose calculation. Informatics and information technology fields undergo constant updating and refinement, allowing the use Monte Carlo Method to simulate brachytherapy source dose distribution. The methodology formalization employed to dosimetric analysis is based mainly in the American Association of Physicists in Medicine (AAPM) studies, by Task Group nº 43 (TG-43) and protocols aimed at dosimetry of these radiation sources types. This work aims to analyze the feasibility of using the MCNP-5C (Monte Carlo N-Particle) code to obtain radiometric parameters of brachytherapy sources and so to study the radiation dose variation in the treatment planning. Simulations were performed for the radiation dose variation in the source plan and determined the dosimetric parameters required by TG-43 formalism for the characterization of the two high dose rate iridium-192 sources. The calculated values were compared with the presents in the literature, which were obtained with different Monte Carlo simulations codes. The results showed excellent consistency with the compared codes, enhancing MCNP-5C code the capacity and viability in the sources dosimetry employed in HDR brachytherapy. The method employed may suggest a possible incorporation of this code in the treatment planning systems provided by manufactures together with the equipment, since besides reducing acquisition cost, it can also make the used computational routines more comprehensive, facilitating the brachytherapy ...

Estudo teórico da contribuição do espalhamento nuclear não elástico na trajetória de prótons de energias entre 50 e 250 MeV em materiais de interesse em radiologia: aplicação em tomografia com prótons

The goal of this work is to study the process of interaction of protons with matter through Monte Carlo simulation. For this purpose, it was employed the SRIM program (Stopping and Range of Ions in Matter ) and MCNPX (Monte Carlo N-Particle eXtended) v2.50. This work is going to support the development of a tomography system with protons. It was studied the interaction of proton with the follow materials: Polimethyl Mehacralate (PMMA), MS20 Tissue Substitute and water. This work employed energies in range of 50 MeV and 250 MeV, that is the range of clinical interest. The energy loss of proton after cross a material layer, the decreasing of its intensity, the angular and lateral de ection of incident beam, including and excluding nuclear interactions. This work is related with Medical Physics and Material Physics, like interaction of radiation with matter, particle transport phenomena, and the experimental methods in Nuclear Physics like simulation and computational by Monte Carlo method

Estudo teórico da contribuição a dose de partículas secundárias geradas por prótons de energias entre 100-200 MeV num phantom de osso compacto

The contribution of the total dose due to deposition of secondary energy particles caused by nuclear inelastic processes (n, 2H, 3H, 3He and  ) in proton therapy is an opened problem and in discussion. In the calculations of plans implemented for routine treatment, the paid dose is calculated whereas that the proton loses energy by ionization and or coulomb excitement. The contribution of inelastic processes associated with nuclear reactions is not considered, mainly due to the difficulty of processing targets consisting of various materials. In this sense, there are only estimates for pure materials or simple composition (water, for example).This work presents the results of simulations by the Monte Carlo method employing the code MCNPX v2.50 (Monte Carlo N-Particle eXtended) of the contribution to the total dose of secondary particles. The study was implemented in a cylindrical phantom composed by compact bone, for monochromatic beams of protons between 100 and 200 MeV with pencil beam form

Viabilidade do Código MCNPX para o Estudo da Técnica de Fluorescência de Raios-X por Reflexão Total

The X-ray fluorescence analysis (XRF) is an important technique for the qualitative and quantitative determination of chemical components in a sample. It is based on measurement of the intensity of the emitted characteristic radiation by the elements of the sample, after being properly excited. One of the modalities of this technique is the total reflection x-ray fluorescence (TXRF). In TXRF, the angle of refraction of the incident beam tends to zero and the refracted beam is tangent to the sample-support interface. Thus, there is a minimum angle of incidence that there is no refracted beam and all the incident radiation undergoes total reflection. As it is implemented in very small samples, in a film format, self-absorption effects should not very relevant. In this study, we evaluated the feasibility of using code MCNPX (Monte Carlo N - Particle eXtended), to simulate a measure implemented by the TXRF technique. In this way, it was verified the quality of response of a system by TXRF spectroscopy using synchrotron radiation as excitation beam for a simple setup, by retrieving the characteristic energies and the concentrations of the elements in the sample. The steps of data processing, after obtaining the excitation spectra, were the same as in a real experiment and included the obtaining of the sensitivity curve for the simulated system. The agreement between the theoretical and simulated values of Ka characteristic energies for different elements was lower than 1 % .The obtained concentration of the elements of the sample had high relatively errors ( between 6 and 60 % ) due mainly to lack of knowing about some realistic physical parameters of the sample , such as density . In this way, this result does not preclude the use of MCNPX code for this type of application

Desenvolvimento, validação, avaliação da incerteza de medição e análise de custos de método baseado em espectroscopia no infravermelho e análise multivariada para previsão de parâmetros de qualidade de amostras de E85

Pós-graduação em Química - IQ

New physics from warped compact extra dimensions: from model building to colliders signals

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A non-homogeneous poisson model with spatial anisotropy applied to ozone data from Mexico City

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Inverted critical adsorption of polyelectrolytes in confinement

What are the fundamental laws for the adsorption of charged polymers onto oppositely charged surfaces, for convex, planar, and concave geometries? This question is at the heart of surface coating applications, various complex formation phenomena, as well as in the context of cellular and viral biophysics. It has been a long-standing challenge in theoretical polymer physics; for realistic systems the quantitative understanding is however often achievable only by computer simulations. In this study, we present the findings of such extensive Monte-Carlo in silico experiments for polymer-surface adsorption in confined domains. We study the inverted critical adsorption of finite-length polyelectrolytes in three fundamental geometries: planar slit, cylindrical pore, and spherical cavity. The scaling relations extracted from simulations for the critical surface charge density sigma(c)-defining the adsorption-desorption transition-are in excellent agreement with our analytical calculations based on the ground-state analysis of the Edwards equation. In particular, we confirm the magnitude and scaling of sigma(c) for the concave interfaces versus the Debye screening length 1/kappa and the extent of confinement a for these three interfaces for small kappa a values. For large kappa a the critical adsorption condition approaches the known planar limit. The transition between the two regimes takes place when the radius of surface curvature or half of the slit thickness a is of the order of 1/kappa. We also rationalize how sigma(c)(kappa) dependence gets modified for semi-flexible versus flexible chains under external confinement. We examine the implications of the chain length for critical adsorption-the effect often hard to tackle theoretically-putting an emphasis on polymers inside attractive spherical cavities. The applications of our findings to some biological systems are discussed, for instance the adsorption of nucleic acids onto the inner surfaces of cylindrical and spherical viral capsids.

Future e(+)e(-) colliders' sensitivity to Hb(b)over-bar coupling and CP violation

A complete analysis of the sensitivity to new Hbb̄ couplings from the process e+e- → bb̄vv̄ at the next generation of linear colliders was performed. These new couplings were predicted by many extensions of the Standard Model. The results are comparable to the study performed previously where a global fit analysis for L=500 fb-1 and √s=500 GeV resulted in a relative accuracy of 2.2% in the gHbb Yukawa coupling.

Computer simulation of configurational properties of partially ionized polyelectrolytes

Monte Carlo simulation methods were used in order to study the conformational properties of partially ionized polyelectrolyte chains with Debye-Hückel screening in 1:1 electrolyte solution at room temperature. Configurational properties such as the distributions of probability for the square end to end distances, for the square radii of gyration and for the angles between polyion bonds were investigated as a function of the chain ionization and the salt concentration. © 1993.

Temperature dependence of conformational properties of short polyelectrolytes from simulations at a single temperature

We use a series expansion method introduced recently by Rickman and Phillpot (Phys. Rev. Lett. 1991, 66, 349) to study the temperature dependent conformational properties of short ionized polyelectrolyte chains in ionic solutions by conducting simulations at a single temperature. The charged beads located at the sites of a cubic lattice interact through screened Coulombic interactions. It is shown that this method provides results that correlate with other Monte Carlo simulations, performed over a range of temperatures, where conformational transitions induced by thermal and screening effects occur. It is also shown that the method can be used successfully when the potential is weakly dependent on temperature. © 1994 American Chemical Society.

The FGM bivariate lifetime copula model: a bayesian approach

In this paper, we propose a bivariate distribution for the bivariate survival times based on Farlie-Gumbel-Morgenstern copula to model the dependence on a bivariate survival data. The proposed model allows for the presence of censored data and covariates. For inferential purpose a Bayesian approach via Markov Chain Monte Carlo (MCMC) is considered. Further, some discussions on the model selection criteria are given. In order to examine outlying and influential observations, we present a Bayesian case deletion influence diagnostics based on the Kullback-Leibler divergence. The newly developed procedures are illustrated via a simulation study and a real dataset.

Estrutura genômica de uma população de suínos base Landrace

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)