Foram medidas distribuições angulares completas do espalhamento elástico do sistema \'ANTPOT. 12 C\' + \'ANTPOT. 24 MG\' nas energias \'E IND. CM\' = 10.67 e 11.33 MeV e entre \'E IND. CM\' = 12.0 e 16.0 MeV, usando feixe de \'ANTPOT. 12 C\' produzido no acelerador Pelletron. Esta faixa de energia se localiza parcialmente abaixo e em torno da barreira coulombiana, estando a barreira em 12.53 MeV. Surpreendentemente todas as distribuições angulares apresentam fortes oscilações mesmo aquelas em energias abaixo da barreira coulombiana. As distribuições angulares foram ajustadas com cálculos de modelo óptico, sendo possível determinar o potencial mais raso, sem ambigüidades contínuas. As principais características deste potencial são: potencial extremamente transparente inclusive no interior nuclear e forte dependência com a energia nas profundidades real e imaginária \'V IND. 0\' e \'W IND. 0\'. Em cinco energias também foram analisadas distribuições angulares do espalhamento inelástico e ajustadas por cálculos de canais acoplados. Os potenciais ópticos usados para diferentes canais apresentam a anomalia do limiar e cálculos de relação de dispersão conectando as integrais de volume dos potenciais ópticos reproduzem bem esta anomalia. / Complete angular distributions of the elastic scattering \'ANTPOT. 12 C\' + \'ANTPOT. 24 MG\' were measured at \'E IND. CM\' = 10.67 and 11.33 MeV and from \'E IND. CM\' = 12.0 to 16.0 MeV, using a \'ANTPOT. 12 C\' beam produced at Pelletron Accelerator. This range of energy is close to the Coulomb barrier of the system, which is 12.53 MeV. Surprisingly all the angular distributions show strong oscillations even at energies bellow the Coulomb barrier. The angular distributions were fitted by optical model calculations and we determined the shallowest real potential, without continuos ambiguity. The main features of this potential are: very transparent even at the nuclear interior and strong dependence with energy of the real and imaginary depths \'V IND. 0\' and \'W IND. 0\'. At five energies the inelastic scattering data were also analysed and well fitted by coupled-channels calculations. The optical potentials of all channels present the threshold anomaly and are well reproduced by dispersion relation calculations applied to the volume integrals of the optical potentials.

<p>A facility for studies of elastic neutron scattering in the 50–130 MeV range has been developed. In addition to elastic neutron scattering, it has been used for (n,p) and (n,d) reaction experiments. The performance of the device has been illustrated in measurements of the (n,p) and (n,n) cross sections on ¹H and ¹²C.</p><p>Elastic neutron scattering from ¹²C and ²⁰⁸Pb has been studied at 96 MeV in the 10–70 degree interval. The achieved energy resolution, 3.7 MeV, is about one order of magnitude better than for any previous experiment above 65 MeV incident energy. The present experiment represents the highest neutron energy where the ground state has been resolved from the first excited state in neutron scattering. A novel method for normalization of the absolute scale of the cross section has been used. The estimated normalization uncertainty, 3 %, is unprecedented for a neutron-induced differential cross section measurement on a nuclear target.</p><p>The results are compared with modern optical model predictions, based on phenomenology or microscopic nuclear theory. The data on ²⁰⁸Pb are in general in good agreement with the theory models.</p><p>All theory models fail to describe the ¹²C data in the 30–50 degree interval, where the models predict a saddle structure not displayed by the present experimental data. Various reasons for this discrepancy have been investigated. For the other parts of the angular range studied, the agreement is good.</p><p>These measurements have to a large degree been motivated by needs in various application areas, i.e., nuclear waste incineration by fast neutrons and biomedical effects caused by neutrons. The implications of the present results on these applications are discussed.</p>

A facility for studies of elastic neutron scattering in the 50–130 MeV range has been developed. In addition to elastic neutron scattering, it has been used for (n,p) and (n,d) reaction experiments. The performance of the device has been illustrated in measurements of the (n,p) and (n,n) cross sections on 1H and 12C. Elastic neutron scattering from 12C and 208Pb has been studied at 96 MeV in the 10–70 degree interval. The achieved energy resolution, 3.7 MeV, is about one order of magnitude better than for any previous experiment above 65 MeV incident energy. The present experiment represents the highest neutron energy where the ground state has been resolved from the first excited state in neutron scattering. A novel method for normalization of the absolute scale of the cross section has been used. The estimated normalization uncertainty, 3 %, is unprecedented for a neutron-induced differential cross section measurement on a nuclear target. The results are compared with modern optical model predictions, based on phenomenology or microscopic nuclear theory. The data on 208Pb are in general in good agreement with the theory models. All theory models fail to describe the 12C data in the 30–50 degree interval, where the models predict a saddle structure not displayed by the present experimental data. Various reasons for this discrepancy have been investigated. For the other parts of the angular range studied, the agreement is good. These measurements have to a large degree been motivated by needs in various application areas, i.e., nuclear waste incineration by fast neutrons and biomedical effects caused by neutrons. The implications of the present results on these applications are discussed.

No description available.

Orientador: Marcio Jose Menon / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-12T16:24:49Z (GMT). No. of bitstreams: 1 Avila_ReginaFonseca_D.pdf: 3530629 bytes, checksum: 01dc8228fc148fa58b57ef51867e8ee9 (MD5) Previous issue date: 2009 / Resumo: Apresentamos um estudo amplo e abrangente do espalhamento elástico de há drons em altas energias através de três abordagens distintas: analítica, empírica e fenomenológica. A primeira 'e caracterizada pelos princípios de analiticidade e cruzamento, limites polinomiais para a amplitude de espalhamento e relações de dispersão. Em especial, para classes de funções de interesse físico, introduzimos novas relações de dispersão derivativas, que são equivalentes às relações de dispersão integrais. Na segunda abordagem, decorrente do princípio de Unitaridade, tratamos a Representação Eiconal. Nesse contexto, a partir de uma parametrização empírica para a amplitude de espalhamento e um método analítico-numérico, determinamos a eiconal no espaço de momento transferido, de forma independente de modelo. Em especial, obtemos evidência estatística de que a parte imaginária da eiconal apresenta um zero (troca de sinal); as implicações desse zero no contexto fenomenológico são discutidas em certo detalhe. Na abordagem fenomenológica, através de um modelo baseado no formalismo de Regge, estudamos as contribuições do Odderon (amplitude ímpar) e Pomeron (amplitude par) no regime de altas energias. Em especial, descrevemos novos procedimentos que podem levar à detecção do Odderon nos experimentos a serem realizados com aceleradores de partículas, o "Relativistic Heavy Íon Collider"(RHIC) e "Large Hadron Collider"(LHC). / Abstract: We investigate high-energy elastic hadron scattering by means of three different approaches: analytical, empirical, and phenomenological. The first one is characterized by the fundamental principles of analyticity and crossing symmetry, polynomial limits for the scattering amplitude and dispersion relations. In special, for classes of functions of physical interest, we introduce novel derivative dispersion relations wich are equivalent to integral dispersion relations. In the second approach, based on unitarity principle, we treat the eikonal representation. In this context, by means of an empirical parametrization for the scattering amplitude and an analytical-numerical method, we extract the eikonal in the momentum transfer space, in a model independent way. In special, we obtain statistical evidence that the imaginary part of eikonal presents a zero (change of sign) in the momentum transfer space; the implication of this zero in the phenomenological context is discussed in certain detail. In the third approach, through a model based on the Regge formalism, we investigate the contributions of the Odderon (odd amplitude) and the Pomeron (even amplitude) in the high energy region. In special, we describe new procedures that can lead to the detection of the Odderon in the experiments to be performed in particle accelerators, Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC). / Doutorado / Fisica-Matematica / Doutor em Matemática Aplicada

Foram medidas distribuições angulares completas do espalhamento elástico do sistema \'ANTPOT. 12 C\' + \'ANTPOT. 24 MG\' nas energias \'E IND. CM\' = 10.67 e 11.33 MeV e entre \'E IND. CM\' = 12.0 e 16.0 MeV, usando feixe de \'ANTPOT. 12 C\' produzido no acelerador Pelletron. Esta faixa de energia se localiza parcialmente abaixo e em torno da barreira coulombiana, estando a barreira em 12.53 MeV. Surpreendentemente todas as distribuições angulares apresentam fortes oscilações mesmo aquelas em energias abaixo da barreira coulombiana. As distribuições angulares foram ajustadas com cálculos de modelo óptico, sendo possível determinar o potencial mais raso, sem ambigüidades contínuas. As principais características deste potencial são: potencial extremamente transparente inclusive no interior nuclear e forte dependência com a energia nas profundidades real e imaginária \'V IND. 0\' e \'W IND. 0\'. Em cinco energias também foram analisadas distribuições angulares do espalhamento inelástico e ajustadas por cálculos de canais acoplados. Os potenciais ópticos usados para diferentes canais apresentam a anomalia do limiar e cálculos de relação de dispersão conectando as integrais de volume dos potenciais ópticos reproduzem bem esta anomalia. / Complete angular distributions of the elastic scattering \'ANTPOT. 12 C\' + \'ANTPOT. 24 MG\' were measured at \'E IND. CM\' = 10.67 and 11.33 MeV and from \'E IND. CM\' = 12.0 to 16.0 MeV, using a \'ANTPOT. 12 C\' beam produced at Pelletron Accelerator. This range of energy is close to the Coulomb barrier of the system, which is 12.53 MeV. Surprisingly all the angular distributions show strong oscillations even at energies bellow the Coulomb barrier. The angular distributions were fitted by optical model calculations and we determined the shallowest real potential, without continuos ambiguity. The main features of this potential are: very transparent even at the nuclear interior and strong dependence with energy of the real and imaginary depths \'V IND. 0\' and \'W IND. 0\'. At five energies the inelastic scattering data were also analysed and well fitted by coupled-channels calculations. The optical potentials of all channels present the threshold anomaly and are well reproduced by dispersion relation calculations applied to the volume integrals of the optical potentials.

Arbitrary high order numerical methods for time-harmonic acoustic scattering problems originally defined on unbounded domains are constructed. This is done by coupling recently developed high order local absorbing boundary conditions (ABCs) with finite difference methods for the Helmholtz equation. These ABCs are based on exact representations of the outgoing waves by means of farfield expansions. The finite difference methods, which are constructed from a deferred-correction (DC) technique, approximate the Helmholtz equation and the ABCs to any desired order. As a result, high order numerical methods with an overall order of convergence equal to the order of the DC schemes are obtained. A detailed construction of these DC finite difference schemes is presented. Details and results from an extension to heterogeneous media are also included. Additionally, a rigorous proof of the consistency of the DC schemes with the Helmholtz equation and the ABCs in polar coordinates is also given. The results of several numerical experiments corroborate the high order convergence of the proposed method. A novel local high order ABC for elastic waves based on farfield expansions is constructed and preliminary results applying it to elastic scattering problems are presented.

Cryogenic electron microscopy (cryo-EM) is an evolving field allowing molecular visu- alizations with picometer resolutions. Images are acquired by shooting electrons through molecular samples and detecting the scattered electrons. From such data, 3D shapes of the molecules can be inversely reconstructed. Currently, describing and simulating the cryo-EM image formation is based either on naive transmittance models or complicated wave-function formalisms. In this thesis, we explore the possibility of simulating cryo-EM image formation via Monte Carlo electron tracing. We combine a delta-tracking algorithm with an elec- tron elastic differential cross-section function and Rutherford formulae to derive two Monte Carlo estimators. The derived models are implemented in a high-performance C++/CUDA environment and compared with other common models. Our particle-based simulated images show considerable similarity to the wave-based state-of-the-art multi- slice model. We also evaluate our models on class averages of real measurements. Both of our proposed models have significantly higher normalized cross-correlation scores with the measured class averages when compared to the most commonly used transmittance model. The thesis proves the viability of a particle-based Monte Carlo simulation of elec- tron microscope...

No description available.

No description available.