480 research outputs found
Identifying structures in the continuum: Application to Be
The population and decay of two-nucleon resonances offer exciting new
opportunities to explore dripline phenomena. The understanding of these systems
requires a solid description of the three-body (core+N+N) continuum. The
identification of a state with resonant character from the background of
non-resonant continuum states in the same energy range poses a theoretical
challenge. It is the purpose of this work to establish a robust theoretical
framework to identify and characterize three-body resonances in a discrete
basis. A resonance operator is proposed, which describes the sensitivity to
changes in the potential. Resonances are then identified from the lowest
eigenstates of the resonance operator. The operator is diagonalized in a basis
of Hamiltonian pseudostates, built within the hyperspherical harmonics
formalism using the analytical THO basis. The energy and width of the resonance
are determined from its time dependence. The method is applied to 16Be in a
14Be+n+n model. An effective core+n potential, fitted to the available
information on the subsystem 15Be, is employed. The 0+ ground state resonance
of 16Be presents a strong dineutron configuration, which favors the picture of
a correlated two-neutron emission. Fitting the three body interaction to the
experimental two-neutron separation energy |S2n|=1.35(10) MeV, the computed
width is Gamma(0+)=0.16 MeV. From the same Hamiltonian, a 2+ resonance is also
predicted with E_r(2+)=2.42 MeV and Gamma(2+)=0.40 MeV. The dineutron
configuration and the computed 0+ width are consistent with previous R-matrix
calculations for the true three-body continuum. The extracted values of the
resonance energy and width converge with the size of the pseudostate basis and
are robust under changes in the basis parameters. This supports the reliability
of the method in describing the properties of unbound core+N+N systems in a
discrete basis.Comment: 11 pages, 14 figures. Accepted as PR
Determining distributions of weakly bound nuclei from breakup cross sections using Continuum Discretized Coupled Channels calculations. Application to Be
A novel method to extract the strength of a weakly bound nucleus from
experimental Coulomb dissociation data is proposed. The method makes use of
continuum discretized coupled channels (CDCC) calculations, in which both
nuclear and Coulomb forces are taken into account to all orders. This is a
crucial advantage with respect to the standard procedure based on the
Equivalent Photon Method (EPM) which does not properly take into account
nuclear distortion, higher order coupling effects, or Coulomb-nuclear
interference terms. The procedure is applied to the Be nucleus using two
sets of available experimental data at different energies, for which seemingly
incompatible have been reported using the EPM. We show that the present
procedure gives consistent strengths, thus solving the aforementioned
long-standing discrepancy between the two measurements.Comment: Submitted for publicatio
Neural Network Local Navigation of Mobile Robots in a Moving Obstacles Environment
IF AC Intelligent Components and Instruments for Control Applications, Budapest, Hungary, 1994This paper presents a local navigation method based on generalized predictive control. A modified cost function to avoid moving and static obstacles is presented. An Extended Kaiman Filter is proposed to predict the motions of the obstacles. A Neural Network implementation of this method is analysed. Simulation results are shown.Ministerio de Ciencia y Tecnología TAP93-0408Ministerio de Ciencia y Tecnología TAP93-058
Determining astrophysical three-body radiative capture reaction rates from inclusive Coulomb break-up measurements
A relationship between the Coulomb inclusive break-up probability and the radiative capture reaction rate for weakly bound three-body systems is established. This direct link provides a robust procedure to estimate the reaction rate for nuclei of astrophysical interest by measuring inclusive break-up processes at different energies and angles. This might be an advantageous alternative to the determination of reaction rates from the measurement of B(E1) distributions through exclusive Coulomb break-up experiments. In addition, it provides a reference to assess the validity of different theoretical approaches that have been used to calculate reaction rates. The procedure is applied to Li11 (Li9+n+n) and He6 (He4+n+n) three-body systems for which some data exist.This work has been partially supported by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (FEDER) under Projects No. FIS2011-28738-c02-01, No. FIS2013-41994-P, No. FPA2013-47327-
C2-1-R, No. FIS2014-53448-c2-1-P, and FIS2014-51941-P and by Junta de Andalucía under Group No. FQM-160 and Project No. P11-FQM-7632. J. Casal acknowledges support from the Ministerio de Educacion, Cultura y Deporte, FPU Research Grant No. AP2010-3124. M. Rodríguez-Gallardo acknowledges postdoctoral support from the Universidad de Sevilla under the V Plan Propio de Investigacion, Contract No. USE-11206-M.Peer Reviewe
Transfer induced by core excitation within an extended distorted-wave Born approximation method
Background: Dynamic core-excitation effects have been found to be of importance in breakup reactions and may be of relevance when obtaining spectroscopic information from transfer reactions. Purpose: In this paper we extend the distorted-wave Born approximation (DWBA) formalism in order to allow for noncentral components in the core-core term appearing in the transition operator, which allows for dynamic core-excitation effects. Then we study these effects by applying the formalism to different (d,p) reactions. Methods: The expression of the nonlocal kernels required for the evaluation of the DWBA amplitudes has been extended so as to include noncentral parts in the core-core interaction. The DWBA scattering amplitude is then obtained by solving the corresponding inhomogeneous equation, with the new computed kernels, and the usual outgoing boundary conditions. A new DWBA code has been developed for this purpose. Results: For Be10(d,p)Be11, core-excitation effects are found to be almost negligible (<3%). The importance of this effect has been found to depend to a large extent on the excitation energy of the core. This has been confirmed in the Ne30(d,p)Ne31 case, for which the excitation energy of the first 2+ state is 0.8 MeV, and the effect of core excitation increases to ≈10%. Conclusions: We find dynamic core-excitation effects in transfer reactions to have small contributions to cross sections, in general. However, they should not be neglected, since they may modify the spectroscopic information obtained from these reactions and may become of importance in reactions with nuclei with a core with high deformation and low excitation energy.Junta de Andalucía FQM160 P07-FQM-02894Ministerio de Economía y Competitividad (España) FPA-2013-47327-C02-01-RPrograma Consolider-Ingenio 2010 (España) CSD2007-00042 FPA2009- 0765
Quantum mechanical description of Stern-Gerlach experiments
The motion of neutral particles with magnetic moments in an inhomogeneous
magnetic field is described in a quantum mechanical framework. The validity of
the semi-classical approximations which are generally used to describe these
phenomena is discussed. Approximate expressions for the evolution operator are
derived and compared to the exact calculations. Focusing and spin-flip
phenomena are predicted. The reliability of Stern-Gerlach experiments to
measure spin projections is assessed in this framework.Comment: 12 pages, 7 eps figures included, revtex, submitted to PR
Breakup mechanisms in the He 6 + Zn 64 reaction at near-barrier energies
New experimental results for the elastic scattering of He6 on Zn64 at incident energies of 15.0 and 18.0 MeV and He4 at 17.5 MeV along with results already published at 10.0 and 13.6 MeV, are presented. Elastic and α experimental cross sections are compared with coupled-reaction-channel, continuum-discretized coupled-channel, and DWBA inclusive-breakup models. The large yield of α particles observed at all measured energies can be explained by considering a nonelastic breakup mechanism.Spanish Ministerio de Economía y Competitividad and FEDER funds (FIS2014-53448-C2-1-P, FIS2017-88410P, FPA2016-77689-C2-1-R)European Union’s Horizon 2020 65400
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