70 research outputs found
Coulomb breakup effects on the optical potentials of weakly bound nuclei
The optical potential of halo and weakly bound nuclei has a long range part
due to the coupling to breakup that damps the elastic scattering angular
distributions. In order to describe correctly the breakup channel in the case
of scattering on a heavy target, core recoil effects have to be taken into
account. We show here that core recoil and nuclear breakup of the valence
nucleon can be consistently taken into account. A microscopic absorptive
potential is obtained within a semiclassical approach and its characteristics
can be understood in terms of the properties of the halo wave function and of
the reaction mechanism. Results for the case of medium to high energy reactions
are presented.Comment: 25 latex pages, 4 tables, 6 figures. Submitted to Nucl. Phys.
Elastic Scattering and Total Reaction Cross Section for the 6He + 27Al System
The elastic scattering of the radioactive halo nucleus 6He on 27Al target was
measured at four energies close to the Coulomb barrier using the RIBRAS
(Radioactive Ion Beams in Brazil) facility. The Sao Paulo Potential(SPP) was
used and its diffuseness and imaginary strength were adjusted to fit the
elastic scattering angular distributions. Reaction cross-sections were
extracted from the optical model fits. The reduced reaction cross-sections of
6He on 27Al are similar to those for stable, weakly bound projectiles as
{6,7}Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al.Comment: 7 pages, 1 table, 3 figure
Reaction mechanisms in the 6Li+59Co system
The reactions induced by the weakly bound 6Li projectile interacting with the
intermediate mass target 59Co were investigated. Light charged particles
singles and - coincidence measurements were performed at the near
barrier energies E_lab = 17.4, 21.5, 25.5 and 29.6 MeV. The main contributions
of the different competing mechanisms are discussed. A statistical model
analysis, Continuum-Discretized Coupled-Channels calculations and two-body
kinematics were used as tools to provide information to disentangle the main
components of these mechanisms. A significant contribution of the direct
breakup was observed through the difference between the experimental sequential
breakup cross section and the CDCC prediction for the non-capture breakup cross
section.Comment: 30 pages, 8 figure
Nothing Lasts Forever: Environmental Discourses on the Collapse of Past Societies
The study of the collapse of past societies raises many questions for the theory and practice of archaeology. Interest in collapse extends as well into the natural sciences and environmental and sustainability policy. Despite a range of approaches to collapse, the predominant paradigm is environmental collapse, which I argue obscures recognition of the dynamic role of social processes that lie at the heart of human communities. These environmental discourses, together with confusion over terminology and the concepts of collapse, have created widespread aporia about collapse and resulted in the creation of mixed messages about complex historical and social processes
Policy recommendations for addressing privacy challenges associated with cell-based research and interventions
Measurement of the cross section of the Li-8(d,alpha)He-6 reaction of possible relevance to big bang nucleosynthesis
We report measurements of the cross section of the Li-8(d, alpha) He-6 reaction in the energy range E-c.m. =2.3-3.5 MeV using a Li-8-radioactive beam on a CD2 foil. The astrophysical S factor and reaction rate were calculated from the measured cross section. The He-6 nuclei produced in the reaction were detected in solidstate detector telescopes. This reaction might have affected the primordial abundance of Li-6 in big bang nucleosynthesis, since He-6 beta decays to Li-6. However, several big bang nucleosynthesis network calculations were found to be insensitive to this reaction, suggesting that the Li-8(d, alpha) He-6 reaction does not affect Li-6 primordial production
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