42 research outputs found
Two-step nuclear reactions: The Surrogate Method, the Trojan Horse Method and their common foundations
In this Letter I argue that the Surrogate Method, used to extract the fast
neutron capture cross section on actinide target nuclei, which has important
practical application for the next generation of breeder reactors, and the
Trojan Horse Method employed to extract reactions of importance to nuclear
astrophysics, have a common foundation, the Inclusive Non-Elastic Breakup
(INEB)Theory. Whereas the Surrogate Method relies on the premise that the
extracted neutron cross section in a (d,p) reaction is predominantly a compound
nucleus one, the Trojan Horse Method, assumes a predominantly direct process
for the secondary reaction induced by the surrogate fragment. In general, both
methods contain both direct and compound contributions, and I show how theses
seemingly distinct methods are in fact the same but at different energies and
different kinematic regions. The unifying theory is the rather well developed
INEB theory.Comment: 3 pages. Accepted for publication in the European Physical Journal A
(2017
Dipole-dipole dispersion interactions between neutrons
We investigate the long-range interactions between two neutrons utilizing
recent data on the neutron static and dynamic electric and magnetic dipole
polarizabilities. The resulting long-range potentials are used to make
quantitative comparisons between the collisions of a neutron with a neutron and
a neutron with a proton. We also assess the importance of the first pion
production threshold and first excited state of the nucleon, the
-resonance ( = + 3/2, I = 3/2). We found both dynamical
effects to be quite relevant for distances r between ~ 50 fm up to ~ fm
in the nn system, the neutron-wall system and in the wall-neutron-wall system,
reaching the expected asymptotic limit beyond that. Relevance of our findings
to the confinement of ultra cold neutrons inside bottles is discussed.Comment: 11 pages, 12 figures, Version to be published in the European
Physical Journal A (2017
Coulomb and nuclear effects in breakup and reaction cross sections
We use a three-body Continuum Discretized Coupled Channel (CDCC) model to
investigate Coulomb and nuclear effects in breakup and reaction cross sections.
The breakup of the projectile is simulated by a finite number of square
integrable wave functions. First we show that the scattering matrices can be
split in a nuclear term, and in a Coulomb term. This decomposition is based on
the Lippmann-Schwinger equation, and requires the scattering wave functions. We
present two different methods to separate both effects. Then, we apply this
separation to breakup and reaction cross sections of 7Li + 208Pb. For breakup,
we investigate various aspects, such as the role of the alpha + t continuum,
the angular-momentum distribution, and the balance between Coulomb and nuclear
effects. We show that there is a large ambiguity in defining the 'Coulomb' and
'nuclear' breakup cross sections, since both techniques, although providing the
same total breakup cross sections, strongly differ for the individual
components. We suggest a third method which could be efficiently used to
address convergence problems at large angular momentum. For reaction cross
sections, interference effects are smaller, and the nuclear contribution is
dominant above the Coulomb barrier. We also draw attention on different
definitions of the reaction cross section which exist in the literature, and
which may induce small, but significant, differences in the numerical values.Comment: 12 pages, 11 figure
Statistical Theory of Breakup Reactions
We propose alternatives to coupled-channels calculations with loosely-bound
exotic nuclei (CDCC), based on the the random matrix (RMT) and the optical
background (OPM) models for the statistical theory of nuclear reactions. The
coupled channels equations are divided into two sets. The first set, described
by the CDCC, and the other set treated with RMT. The resulting theory is a
Statistical CDCC (CDCC), able in principle to take into account many pseudo
channels.Comment: 15 pages, 4 figures. Contribution to: "4th International Workshop on
Compound-Nuclear Reactions and Related Topics (CNR*13)", October 7-11, 2013,
Maresias, Brazi
ENERGIA NUCLEAR
In this article we will address some important considerations on the use of nuclear energy. We will answers of general interest to the public, such as: What is nuclear energy? Why do reactors use uranium as fuel? How can we assess the safety in nuclear plants when there are seismic events? What is the role of the International Atomic Energy Agency?Abordamos neste artigo algumas considerações importantessobre o uso da energia nuclear. Respondemos questões de interesse para o público como: o que é energia nuclear; que usar urânio como combustÃvel nos reatores; como avaliar a segurança da usinas no caso de abalos sÃsmicos; e qual função da Agência Internacional de Energia Atômica
Weak nonmesonic decay spectra of hypernuclei
We compute one- and two-nucleon kinetic-energy spectra and opening-angle
distributions for the nonmesonic weak decay of several hypernuclei, and compare
our results with some recent data. The decaymics is described by transition
potentials of the one-meson-exchange type, and the nuclear structure aspects by
two versions of the independent-particle shell model (IPSM). In version IPSM-a,
the hole states are treated as stationary, while in version IPSM-b the deep
hole states are considered to be quasi-stationary and are described by
Breit-Wigner distributions.Comment: 3 pages 2 figures. To be published in Nucl. Phys. A; Contribution to
the NN2009 International Conference, Beijing, China, August 200
Semi-classical scattering in two dimensions
The semi-classical limit of quantum-mechanical scattering in two dimensions
(2D) is developed. We derive the Wentzel-Kramers-Brillouin and Eikonal results
for 2D scattering. No backward or forward glory scattering is present in 2D.
Other phenomena, such as rainbow or orbiting do show up.Comment: 6 page