Mechanisms of direct reactions with halo nuclei

Halo nuclei are exotic nuclei which exhibit a strongly clusterised structure: they can be seen as one or two valence nucleons loosely bound to a core. Being observed at the ridge of the valley of stability, halo nuclei are studied mostly through reactions. In this contribution the reaction models most commonly used to analyse experimental data are reviewed and compared to one another. A reaction observable built on the ratio of two angular distributions is then presented. This ratio enables removing most of the sensitivity to the reaction mechanism, which emphasises the effects of nuclear structure on the reaction.Comment: Invited talk given by Pierre Capel at the "10th International Conference on Clustering Aspects of Nuclear Structure and Dynamics" (Cluster12), Debrecen, Hungary, 24-28 September 2012. To appear in the Cluster12 Proceedings in the Open Access Journal of Physics: Conference Series (JPCS). (5 pages, 3 figures

Coupling and higher-order effects in the 12C(d,p)13C and 13C(p,d)12C reactions

Coupled channels calculations are performed for the 12C(d,p)13C and 13C(p,d)12C reactions between 7 and 60 MeV to study the effect of inelastic couplings in transfer reactions. The effect of treating transfer beyond Born approximation is also addressed. The coupling to the 12C 2+ state is found to change the peak cross-section by up to 15 %. Effects beyond Born approximation lead to a significant renormalization of the cross-sections, between 5 and 10 % for deuteron energies above 10 MeV, and larger than 10 % for lower energies. We also performed calculations including the remnant term in the transfer operator, which has a small impact on the 12C(d,p)13C(g.s.) and 13C(p,d)12C(g.s.) reactions. Above 30 MeV deuteron energy, the effect of the remnant term is larger than 10 % for the 12C(d,p)13C(3.09 MeV) reaction and is found to increase with decreasing neutron separation energy for the 3.09 MeV state of 13C. This is of importance for transfer reactions with weakly bound nuclei.Comment: 7 pages, 7 figures, submitted to Phys. Rev.

Nonlinear dynamics of relativistic charged particle beams

The idea behind this work is to analyze the transversal dynamics of a relativistic charged particle beam. The beam is azimuthally symmetric, focused by a constant magnetic field and supposed to be initially cold. While mismatched, nonrelativistic, and homogeneous beams oscillate with an invariant cold density profile, it is shown that relativistic homogeneous beams progressively heat and lose an important amount of constituents during its magnetic confinement. This heating process starts with phase-space wave-breaking, a mechanism observed before in initially inhomogeneous beams. The results have been obtained with full self-consistent N-particle beam numerical simulations

Recent developments in the eikonal description of the breakup of exotic nuclei

The study of exotic nuclear structures, such as halo nuclei, is usually performed through nuclear reactions. An accurate reaction model coupled to a realistic description of the projectile is needed to correctly interpret experimental data. In this contribution, we briefly summarise the assumptions made within the modelling of reactions involving halo nuclei. We describe briefly the Continuum-Discretised Coupled Channel method (CDCC) and the Dynamical Eikonal Approximation (DEA) in particular and present a comparison between them for the breakup of 15C on Pb at 68AMeV. We show the problem faced by the models based on the eikonal approximation at low energy and detail a correction that enables their extension down to lower beam energies. A new reaction observable is also presented. It consists of the ratio between angular distributions for two different processes, such as elastic scattering and breakup. This ratio is completely independent of the reaction mechanism and hence is more sensitive to the projectile structure than usual reaction observables, which makes it a very powerful tool to study exotic structures far from stability.Comment: Contribution to the proceedings of the XXI International School on Nuclear Physics and Applications & the International Symposium on Exotic Nuclei, dedicated to the 60th Anniversary of the JINR (Dubna) (Varna, Bulgaria, 6-12 September 2015), 7 pages, 4 figure

Distribuição espacial da comunidade de insetos-praga em soja cultivada em sistema silviagrícola

A amostragem é uma etapa fundamental do manejo integrado de pragas, pois permiti avaliar quando as pragas atingem seus níveis de controle. Considerando que a integração de espécies vegetais pode influenciar na distribuição espacial dos insetos, objetivou-se avaliar se o método de caminhamento aleatório na cultura da soja em monocultivo pode ser utilizado em soja cultivada em sistemas silviagrícolas. Avaliou-se 12 parcelas de 2 ha cada contendo três ranks de três linhas de eucalipto (árvores com 2,5 anos) espaçados a cada 30m, sendo que nos espaços entre ranks foi cultivada a soja. As avaliações foram realizadas semanalmente, avaliando-se três pontos (1m da cultura) por parcela pelo método do pano de batida. As coordenadas dos pontos de amostragem foram: i: rente à face sul dos ranks; ii. entre os ranks (aproximadamente 15m dos ranks) e, iii. rente à face norte dos ranks. Durante o cultivo da soja, a projeção da sombra do eucalipto estava na face sul. Observou-se que entre os lepidópteros, a presença de Anticarsia gemmatalis, espécies de Plusinae e de Spodoptera spp. foi significativamente maior entre os rankse Heliothinae não diferiu significativamente entre os pontos de amostragem. No entanto, ao avaliar a porcentagem de desfolha, não houve diferença significativa entre os locais. Ao avaliar a população de percevejos, constatou-se que Euschistus heros preferiu significativamente plantas localizadas na face sul dos ranks. Entretanto, Dichelops spp. preferiu significativamente plantas localizadas na face norte dos ranks. Portanto, tornar-se importante em sistemas silviagrícolas, a priorização de amostragens rentes as laterais dos ranks devido à diferença na distribuição espacial de espécies de percevejos em função da projeção da sombra proporcionada pelo componente florestal e por não haver diferença espacial significativa na desfolha provocada pelos lepidópteros

Nuclear reaction studies of unstable nuclei using relativistic mean field formalisms in conjunction with Glauber model

We study nuclear reaction cross-sections for stable and unstable projectiles and targets within Glauber model, using densities obtained from various relativistic mean field formalisms. The calculated cross-sections are compared with the experimental data in some specific cases. We also evaluate the differential scattering cross-sections at several incident energies, and observe that the results found from various densities are similar at smaller scattering angles, whereas a systematic deviation is noticed at large angles. In general, these results agree fairly well with the experimental data.Comment: 9 pages, 7 figures, submitted to PR