Abstract-The Geant4 toolkit offers a rich variety of electromagnetic physics models; so far the evaluation of this Geant4 domain has been mostly focused on its physics functionality, while the features of its design and their impact on simulation accuracy, computational performance and facilities for verification and validation have not been the object of comparable attention yet, despite the critical role they play in many experimental applications. A new project is in progress to study the application of new design concepts and software techniques in Geant4 electromagnetic physics, and to evaluate how they can improve on the current simulation capabilities. The application of a policy-based class design is investigated as a means to achieve the objective of granular decomposition of processes; this design technique offers various advantages in terms of flexibility of configuration and computational performance. The current Geant4 physics models have been re-implemented according to the new design as a pilot project. The main features of the new design and first results of performance improvement and testing simplification are presented; they are relevant to many Geant4 applications, where computational speed and the containment of resources invested in simulation production and quality assurance play a critical role.
Radionuclides deposited internally in the mother will give rise to a radiation dose in the infant in two ways. The radionuclides may be transferred through milk and give rise to an internal dose in the infant, or the radionuclides may emit photons that are absorbed by the infant, giving rise to an external dose. In this paper, the external dose to the newborn infant caused by direct irradiation was estimated for monoenergetic photons. Voxel models (also called voxel phantoms) of the mother and infant were made in three geometries. These models, consisting of volume elements, or voxels, were designed so that the infant model was placed in the lap, at the breast and on the shoulder of the mother model. The Visual Monte Carlo (VMC) code was used to transport the photons through the voxel models. Source regions for the emitted photons, such as the whole body, the thyroid, the lung, the liver and the skeleton, were chosen. For the validation of the calculation procedure, VMC results were favourably compared with the results obtained by using other Monte Carlo programs and also with the previously published results for specific absorbed fractions. This paper provides estimates of the external dose per photon to the infant for photon energies between 0.05 and 2.5 MeV. The external dose per photon estimates were made for the three geometries and for the sources listed above. The results show that, for the geometry of the nursing infant model at the breast, the highest dose to the infant per photon comes from radionuclides deposited in the mother's liver. For the nursing infant model at the shoulder, the highest dose to the infant per photon comes from radionuclides deposited in the mother's thyroid, and for the nursing infant model in the lap, the highest dose to the infant per photon comes from radionuclides deposited uniformly in the whole body. The dose per photon results were then used to estimate the dose an infant might receive over the lactation period (6 months) due to the incorporation of 1 Bq of a radionuclide by the mother. This information may be used to provide external dose estimates to the infant in the case of a known or suspected radionuclide incorporation by the mother due to, for example, a nuclear medicine procedure.
Anualmente, diversos radiofármacos são utilizados em mais de 50 procedimentos clínicos diferentes em todo o Brasil. Sendo assim, profissionais inseridos nas diversas práticas de Medicina Nuclear que envolvem atividades ligadas a radio-emissores de alta energia representam um grupo de maior exposição à radiação e justificam esforços permanentes na otimização de riscos radiológicos. A utilização de técnicas avançadas de monitoração representa um importante subsídio para a avaliação da exposição ocupacional em instalações e a consequente redução das doses individuais. Neste trabalho foi feita a implementação de um fantoma de mão e antebraço em código Geant4, para a avaliação da exposição ocupacional de extremidades de trabalhadores que realizam práticas de Medicina Nuclear. O modelo de simulação oferecido pelo Geant4 inclui um conjunto completo de recursos, com a reconstrução de trajetórias, geometrias e modelos físicos. Para este trabalho, os valores calculados em simulação são comparados com as taxas medidas por dosímetros termoluminescentes (TLDs) em fantoma físico REMAB®. A partir da análise dos dados obtidos através da simulação e experimentação, dentre os 14 pontos estudados, observouse uma discrepância de até 8,2% dos valores de kerma encontrados. O fantoma geométrico implementado em código de Monte Carlo Geant4 foi devidamente validado e poderá ser usado, posteriormente, para a avaliação de doses em extremidades.
Para o caso de uma estimativa do risco decorrente da exposição de um indivíduo que tenha sido externamente exposto à radiação ionizante, principalmente no que se refere aos efeitos determinísticos e estocásticos à saúde humana, a avaliação de dose efetiva de radiação recebida é uma das informações mais expressivas para essa avaliação. Dessa maneira, devido ao labiríntico sistema utilizado em questão -o corpo humano -essa avaliação deve ser feita utilizando os simuladores físicos, mais conhecidos como fantomas (do inglês, phantoms). A ICRP em sua publicação 110 introduz os fantomas masculino e feminino de Voxel e na publicação 116, apresenta os coeficientes de conversão kerma no ar para dose absorvida em órgãos que se submetam a exposições externas à radiação em um feixe paralelo monoenergético a fótons. Dessa maneira, o presente trabalho pretende realizar uma modelagem da anatomia humana utilizando modelos de Voxels aplicados ao Código Monte Carlo e, através do software Visual Monte Carlo, que simula a irradiação do corpo humano. Fazendo, futuramente, uma avaliação de ambos os resultados com os limites de validade das expressões do TECDOC-1162 da IAEA para o caso de fonte puntiforme.
Occupational neutron fields usually have energies from the thermal range to some MeV and the characterization of the spectra is essential for estimation of the radioprotection quantities. Thus, the spectrum must be unfolded based on a limited number of measurements. This study implemented an algorithm based on the bee colonies behavior, named Artificial Bee Colony (ABC), where the intelligent behavior of the bees in search of food is reproduced to perform the unfolding of neutron spectra. The experimental measurements used Bonner spheres and 6LiI (Eu) detector, with irradiations using a thermal neutron flux and three reference fields: 241Am-Be, 252Cf and 252Cf (D2O). The ABC obtained good estimation of the expected spectrum even without previous information and its results were closer to expected spectra than those obtained by the SPUNIT algorithm.
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