706 research outputs found
As festas clássicas de Siracussa
(Primeiro Parágrafo do Artigo)O problema que se nos apresenta, todas as vezes em que o Instituto do Drama Antigo anuncia, representações no teatro grego de Siracusa, na SicĂlia, Ă© o do homem novo colocado diante da velha tragĂ©dia, das suas reações, das suas atrações e repulsas, das transformações do espĂrito humano, de tudo quanto o espectador moderno possa extrair da tragĂ©dia antiga
Trojan Horse as an indirect technique in nuclear astrophysics. Resonance reactions
The Trojan Horse method is a powerful indirect technique that provides
information to determine astrophysical factors for binary rearrangement
processes at astrophysically relevant energies by measuring
the cross section for the Trojan Horse reaction in
quasi-free kinematics. We present the theory of the Trojan Horse method for
resonant binary subreactions based on the half-off-energy-shell R matrix
approach which takes into account the off-energy-shell effects and initial and
final state interactions.Comment: 6 pages and 1 figur
Influence of the Electronic Chaotic Motion on the Fusion Dynamics at Astrophysical Energies
We perform semi-classical molecular dynamics simulations of screening by
bound electrons in low energy nuclear reactions. In our simulations quantum
effects corresponding to the Pauli and Heisenberg principle are enforced by
constraints. In addition to the well known adiabatic and sudden limits, we
propose a new "dissipative limit" which is expected to be important not only at
high energies but in the extremely low energy region. The dissipative limit is
associated with the chaotic behavior of the electronic motion. It affects also
the magnitude of the enhancement factor. We discuss also numerical experiments
using polarized targets. The derived enhancement factors in our simulation are
in agreement with those extracted within the -matrix approach.Comment: 17 pages, 9 figure
Silicon detectors for the n-TOF neutron beams monitoring
During 2014 the second experimental area EAR2 was completed at the n-TOF
neutron beam facility at CERN. As the neutrons are produced via spallation, by
means of a high-intensity 20 GeV pulsed proton beam impinging on a thick
target, the resulting neutron beam covers an enormous energy range, from
thermal to several GeV. In this paper we describe two beam diagnostic devices,
designed and built at INFN-LNS, both exploiting silicon detectors coupled with
neutron converter foils containing 6Li. The first one is based on four silicon
pads and allows to monitor the neutron beam flux as a function of the neutron
energy. The second one, based on position sensitive silicon detectors, is
intended for the reconstruction of the beam profile, again as a function of the
neutron energy. Several electronic setups have been explored in order to
overcome the issues related to the gamma flash, namely a huge pulse present at
the start of each neutron bunch which may blind the detectors for some time.
The two devices have been characterized with radioactive sources at INFN-LNS
and then tested at n-TOF. The wide energy and intensity range they proved
capable of sustaining, made them quite attractive and suitable to be used in
both EAR1 and EAR2 n-TOF experimental areas, where they became immediately
operational.Comment: submitted to Review of Scientific Instrument
Solving the large discrepancy between inclusive and exclusive measurements of the reaction cross section at astrophysical energies
A solution of the large discrepancy existing between inclusive and exclusive
measurements of the reaction
cross section at MeV is evaluated. This problem has profound
astrophysical relevance for this reaction is of great interest in Big-Bang and
r-process nucleosynthesis. By means of a novel technique, a comprehensive study
of all existing cross section
data is carried out, setting up a consistent picture in which all the inclusive
measurements provide the reliable value of the cross section. New unambiguous
signatures of the strong branch pattern non-uniformities, near the threshold of
higher excited levels, are presented and their possible
origin, in terms of the cluster structure of the involved excited states of
and nuclei, is discussed.Comment: 5 pages, 4 figures, 1 tabl
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