Fusion cross section measurements of astrophysical interest for light heavy ions systems within the STELLA project

This contribution is focused on the STELLA project (STELlar LAboratory), which aims at the measurement of fusion cross sections between light heavy ions like 12C+12C, 12C+16O or 16O+16O at deep subbarrier energies. The gamma-particle coincidence technique is used in order to reduce background contributions that become dominant for measurements in the nanobarn regime. The experimental setup composed of an ultra high vacuum reaction chamber, a set of 3 silicon strip detectors, up to 36 LaBr3(Ce) scintillators from the UK FATIMA collaboration, and a fast rotating target system will be described. The 12C+12C fusion reaction has been studied from Elab = 11 to 5.6 MeV using STELLA at the Andromède facility in Orsay, France. Preliminary commissioning results are presented in this article

Contextualização no ensino de estatística: uma proposta para os anos finais do ensino fundamental

Acompanha: Sequência de ensino contemplando a estatística nos anos finais do ensino fundamental segundo pressupostos da contextualizaçãoThe present study aimed to examine the contributions that a sequence of teaching based on assumptions of contextualization can bring to the teaching of statistics in the final years of basic school. The literature review concerning the teaching of statistics relies on Cazorla (2002), Lopes (2003, 2008, 2010a, 2010b), Silva (2007), Andrade (2008), Cazorla, Kataoka and Silva (2010), Jacobini et al. (2010), Campos, Wodewotzki and Jacobini (2011), among others. As for context, the literature review supported by Brazil (1998b, 1999), Tufano (2001), Pais (2002, 2010), Ramos (2004), (2005), Sadovsky (2007), Luccas (2011), among others. With the intention of achieving the proposed goal, was developed in the year 2011 a applied research, interpretive analysis and qualitative, descriptive in a batch of students of 7° year of basic school to a State public College of the city of Ponta Grossa, Paraná. The review of literature pertaining to the search features based on Gil (1991, 2006), Chizzotti (2003, 2008), Silva and Menezes (2005), Moreira and Caleffe (2008), Alves-Mazzotti (2011), Sarmento (2011), Teixeira (2011), among others. First was conducted an analysis of previous performance of the students on the basic content of statistics, based on a diagnostic instrument called pre-test. Then it was applied a sequence of teaching directed to basic statistical content, through the use of data collected in their own class, i.e. through contextualization. It emerged during the implementation of education, a greater interest and motivation of students to classes, as well as greater involvement of learners with the contents. The results of the analysis of the performance of the students after teaching sequence showed that this contributed to a significant gain on the acquisition of basic statistical content by students of the final years basic school. It is considered that the activities undertaken with learners, contributed to the development of the skills of reasoning, thinking, and statistical literacy of those forming the necessary basis for that in the future these students can reach the level of statistical literacy that contemporary society requires. As the final product of this work was to elaborate a courseware to support teacher education sequence containing a contextualized on basic statistical content aimed at the basic school, which is attached to this dissertation.O presente trabalho teve como objetivo analisar as contribuições que uma sequência de ensino pautada nos pressupostos da contextualização poderá trazer para o ensino e aprendizagem de Estatística nos anos finais do Ensino Fundamental. A revisão de literatura referente ao ensino de Estatística apoia-se em Cazorla (2002), Lopes (2003, 2008, 2010a, 2010b), Silva (2007), Andrade (2008), Cazorla, Kataoka e Silva (2010), Jacobini et al. (2010), Campos, Wodewotzki e Jacobini (2011), dentre outros. Quanto a contextualização, a revisão de literatura apoia-se em Brasil (1998b, 1999), Tufano (2001), Pais (2002, 2010), Ramos (2004), Mello (2005), Sadovsky (2007), Luccas (2011), além de outros. Com a intenção de alcançar o objetivo proposto, foi desenvolvida no ano de 2011 uma pesquisa aplicada, qualitativa com análise interpretativa e, descritiva em uma turma de alunos do 7° ano do Ensino Fundamental de um colégio público estadual do município de Ponta Grossa, Paraná. A revisão de literatura referente às características da pesquisa fundamenta-se em Gil (1991, 2006), Chizzotti (2003, 2008), Silva e Menezes (2005), Moreira e Caleffe (2008), Alves-Mazzotti (2011), Sarmento (2011), Teixeira (2011), dentre outros. Primeiramente foi realizada uma análise do desempenho prévio dos alunos em relação a conteúdos básicos de Estatística, tendo como base um instrumento diagnóstico chamado pré – teste. Depois foi aplicada uma sequência de ensino direcionada a conteúdos básicos de Estatística, por meio da utilização de dados coletados na própria turma, ou seja, por meio da contextualização. Verificou-se durante a aplicação da sequência de ensino, um maior interesse e motivação dos alunos para as aulas, além de um maior envolvimento dos educandos com os conteúdos estudados. Os resultados da análise do desempenho dos alunos após a aplicação da sequência de ensino mostraram que essa contribuiu para que houvesse um ganho significativo quanto à aquisição de conteúdos básicos de Estatística por parte de educandos dos anos finais do Ensino Fundamental. Considera-se que as atividades realizadas com os educandos, contribuíram para o desenvolvimento das competências de raciocínio, pensamento e, letramento estatísticos desses, formando a base necessária para que futuramente esses alunos possam atingir o nível de letramento estatístico que a sociedade contemporânea exige. Como produto final deste trabalho foi elaborado um material didático de apoio ao professor contendo uma sequência de ensino contextualizada sobre conteúdos básicos de Estatística voltada ao Ensino Fundamental, o qual se encontra anexado a esta dissertação

Fusion Cross Sections of Astrophysics Interest Within the STELLA Project

International audienceLow energy fusion between light heavy-ions is a key feature of the evolution of massive stars. In systems of astrophysical interest, the process may be strongly affected by molecular configurations of the compound nucleus, leading to resonant S factors. In particular, the 12C+12C fusion reaction has been the object of numerous experimental investigations. The STELLA project has been developed to extend these investigations to lower energies towards the Gamow window

Fusion hindrance for the positive QQ-value system 12C+30Si^{12}\mathrm{C}+^{30}\mathrm{Si}

International audienceBackground: The fusion reaction C12+Si30 is a link between heavier cases studied in recent years, and the light heavy-ion systems, e.g., C12+C12, O16+O16 that have a prominent role in the dynamics of stellar evolution. C12+Si30 fusion itself is not a relevant process for astrophysics, but it is important to establish its behavior below the barrier, where couplings to low-lying collective modes and the hindrance phenomenon may determine the cross sections. The excitation function is presently completely unknown below the barrier for the C12+Si30 reaction, thus no reliable extrapolation into the astrophysical regime for the C+C and O+O cases can be performed. Purpose: Our aim was to carry out a complete measurement of the fusion excitation function of C12+Si30 from well below to above the Coulomb barrier, so as to clear up the consequence of couplings to low-lying states of Si30, and whether the hindrance effect appears in this relatively light system which has a positive Q value for fusion. This would have consequences for the extrapolated behavior to even lighter systems. Methods: The inverse kinematics was used by sending Si30 beams delivered from the XTU Tandem accelerator of INFN-Laboratori Nazionali di Legnaro onto thin C12 (50μg/cm2) targets enriched to 99.9% in mass 12. The fusion evaporation residues (ER) were detected at very forward angles, following beam separation by means of an electrostatic deflector. Angular distributions of ER were measured at Ebeam=45, 59, and 80 MeV, and they were angle integrated to derive total fusion cross sections. Results: The fusion excitation function of C12+Si30 was measured with high statistical accuracy, covering more than five orders of magnitude down to a lowest cross section ≃3μb. The logarithmic slope and the S factor have been extracted and we have convincing phenomenological evidence of the hindrance effect. These results have been compared with the calculations performed within the model that considers a damping of the coupling strength well inside the Coulomb barrier. Conclusions: The experimental data are consistent with the coupled-channels calculations. A better fit is obtained by using the Yukawa-plus-exponential potential and a damping of the coupling strengths inside the barrier. The degree of hindrance is much smaller than the one in heavier systems. Also a phenomenological estimate reproduces quite closely the hindrance threshold for C12+Si30, so that an extrapolation to the C+C and O+O cases can be reliably performed