6,247 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
Reactions induced by Be in a four-body continuum-discretized coupled-channels framework
We investigate the elastic scattering of Be on Pb at beam
energies above (50 MeV) and below (40 MeV) the Coulomb barrier. The reaction is
described within a four-body framework using the Continuum-Discretized
Coupled-Channels (CDCC) method. The Be projectile states are generated
using the analytical Transformed Harmonic Oscillator (THO) basis in
hyperspherical coordinates. Our calculations confirm the importance of
continuum effects at low energies.Comment: 2 pages, 1 figure. Proceedings of the International Scientific
Meeting on Nuclear Physics, RABIDA15, La R\'abida (Spain), June 1-5, 201
Analytical transformed harmonic oscillator basis for three-body nuclei of astrophysical interest: Application to 6He
Recently, a square-integrable discrete basis, obtained performing a simple
analytical local scale transformation to the harmonic oscillator basis, has
been proposed and successfully applied to study the properties of two-body
systems. Here, the method is generalized to study three-body systems. To test
the goodness of the formalism and establish its applicability and limitations,
the capture reaction rate for the nucleosynthesis of the Borromean nucleus 6He
(4He + n + n) is addressed. Results are compared with previous publications and
with calculations based on actual three-body continuum wave functions, which
can be generated for this simple case. The obtained results encourage the
application to other Borromean nuclei of astrophysical interest such as 9Be and
12C, for which actual three-body continuum calculations are very involved.Comment: Accepted in Phys. Rev.
Linking structure and dynamics in reactions with Borromean nuclei: the LiLi case
One-neutron removal reactions induced by two-neutron Borromean
nuclei are studied within a Transfer-to-the-Continuum (TC) reaction framework,
which incorporates the three-body character of the incident nucleus. The
relative energy distribution of the residual unbound two-body subsystem, which
is assumed to retain information on the structure of the original three-body
projectile, is computed by evaluating the transition amplitude for different
neutron-core final states in the continuum. These transition amplitudes depend
on the overlaps between the original three-body ground-state wave function and
the two-body continuum states populated in the reaction, thus ensuring a
consistent description of the incident and final nuclei. By comparing different
Li three-body models, it is found that the LiLi
relative energy spectrum is very sensitive to the position of the and
states in Li and to the partial wave content of these
configurations within the Li ground-state wave function. The possible
presence of a low-lying resonance is discussed. The coupling of the
single particle configurations with the non-zero spin of the Li core,
which produces a spin-spin splitting of the states, is also studied. Among the
considered models, the best agreement with the available data is obtained with
a Li model that incorporates the actual spin of the core and contains
31\% of -wave content in the -Li subsystem, in accord
with our previous findings for the Li(p,d)Li transfer reaction,
and a near-threshold virtual state.Comment: 7 pages, 4 figures, submitted to PL
Description of the LiLi transfer reaction using structure overlaps from a full three-body model
Recent data on the differential angular distribution for the transfer
reaction Li(p,d)Li at MeV in inverse kinematics are
analysed within the DWBA reaction framework, using the overlap functions
calculated within a three-body model of Li. The weight of the different
Li configurations in the system's ground state is obtained from the
structure calculations unambiguously. The effect of the Li spin in the
calculated observables is also investigated. We find that, although all the
considered models succeed in reproducing the shape of the data, the magnitude
is very sensitive to the content of wave in the Li
ground-state wave function. Among the considered models, the best agreement
with the data is obtained when the Li ground state contains a 31\%
of wave in the -Li subsystem. Although this model takes into
account explicitly the splitting of the and resonances due to the
coupling of the wave to the spin of the core, a similar
degree of agreement can be achieved with a model in which the Li spin is
ignored, provided that it contains a similar p-wave content.Comment: 8 pages, 3 figures. Final versio
Transportation of hazardous materials via pipeline. A historical overview
The transportation of hazardous materials via pipelines is often considered a safer alternative to other transportation modalities such as railway, road and ship. However, pipelines often cross industrial and highly populated areas, so that their failure can pose a significant risk to the surrounding environment and the exposed population: the possible release of flammable and/or toxic materials in such areas can generate catastrophic events with very severe consequences. A number of accidents have actually occurred in the past years, and even when no deaths or injured are reported, significant damages to the surrounding environment often occur. This suggests that, given the extremely wide extension of the network worldwide, and the very high amounts of transported materials, a careful analysis is still required. In addition, the construction of pipelines also involves the contribution of expertise from a range of technical areas. As a consequence, the occurrence of accidents and the impact of their consequences, depend on the combination of a large number of parameters. In the present paper, an analysis of data relative to pipelines transporting hazardous materials has been carried out, and the influence of specific issues connected with their type and operation, has been assessed
Investigating the 10Li continuum through 9Li(d,p)10Li reactions
The continuum structure of the unbound system Li, inferred from the
LiLi transfer reaction, is reexamined. Experimental data for
this reaction, measured at two different energies, are analyzed with the same
reaction framework and structure models. It is shown that the seemingly
different features observed in the measured excitation energy spectra can be
understood as due to the different incident energy and angular range covered by
the two experiments. The present results support the persistence of the
parity inversion beyond the neutron dripline as well as the splitting of the
well-known low-lying -wave resonance. Furthermore, they provide indirect
evidence that most of the single-particle strength, including possible
resonances, lies at relatively high excitations energies.Comment: accepted for publication in Physics Letters
Two-nucleon emitters within a pseudostate method: The case of Be and Be
Background: Since the first experimental observation, two-nucleon
radioactivity has gained renewed attention over the past fifteen years. The
Be system is the lightest two-proton ground-state emitter, while Be
has been recently proposed to be the first two-neutron ground-state emitter
ever observed. A proper understanding of their properties and decay modes
requires a reasonable description of the three-body continuum.
Purpose: Study the ground-state properties of Be and Be within a
general three-body model and investigate their nucleon-nucleon correlations in
the continuum.
Method: The pseudostate (PS) method in hyperspherical coordinates, using the
analytical transformed harmonic oscillator (THO) basis for three-body systems,
is used to construct the Be and Be ground-state wave functions.
These resonances are approximated as a stable PS around the known two-nucleon
separation energy. Effective core- potentials, constrained by the available
experimental information on the binary subsystems Li and Be, are
employed in the calculations.
Results: The ground state of Be is found to present a strong dineutron
configuration, with the valence neutrons occupying mostly an state
relative to the core. The results are consistent with previous -matrix
calculations for the actual continuum. The case of Be shows a clear
symmetry with respect to its mirror partner, the two-neutron halo He: The
diproton configuration is dominant, and the valence protons occupy an
orbit.
Conclusions: The PS method is found to be a suitable tool in describing the
properties of unbound ground states. For both Be and
Be, the results are consistent with previous theoretical studies and
confirm the dominant dinucleon configuration. This favors the picture of a
correlated two-nucleon emission.Comment: 10 pages, 12 figures; accepted as PR
Radiative capture reaction for Ne formation within a full three-body model
Background: The breakout from the hot Carbon-Nitrogen-Oxigen (CNO) cycles can
trigger the rp-process in type I x-ray bursts. In this environment, a
competition between and the
two-proton capture reaction is
expected.
Purpose: Determine the three-body radiative capture reaction rate for
formation including sequential and direct, resonant and
non-resonant contributions on an equal footing.
Method: Two different discretization methods have been applied to generate
Ne states in a full three-body model: the analytical transformed
harmonic oscillator method and the hyperspherical adiabatic expansion method.
The binary --O interaction has been adjusted to reproduce the known
spectrum of the unbound F nucleus. The dominant contributions to
the reaction rate have been
calculated from the inverse photodissociation process.
Results: Three-body calculations provide a reliable description of Ne
states. The agreement with the available experimental data on Ne is
discussed. It is shown that the
reaction rates computed within the two methods agree in a broad range of
temperatures. The present calculations are compared with a previous theoretical
estimation of the reaction rate.
Conclusions: It is found that the full three-body model provides a reaction
rate several orders of magnitude larger than the only previous estimation. The
implications for the rp-process in type I x-ray bursts should be investigated.Comment: 10 pages, 10 figures. Corrected versio
Descriptive and spatial epidemiology of bovine cysticercosis in North-Eastern Spain (Catalonia).
From March 2005 to December 2007, 284 animals from 67 cattle farms (24 dairy and 43 beef) affected by bovine cysticercosis were detected in the region of Catalonia (North-Eastern Spain). Dairy farms were almost twice more likely to be affected than beef farms (OR=1.79, 95% CI=1.08-2.96, p<0.05), and infected premises have a statistically significant (p<0.05) larger number of animals when compared to uninfected farms in Catalonia. The geographical distribution of the infected farms was evaluated and two statistically significant clusters were identified. The most likely cluster was located in the western part of the study region, with 8 out of 10 farms infected. Epidemiological investigations revealed that the 8 farms belonged to the same company. The secondary cluster was located in Eastern Catalonia with 12 infected farms out of 167 cattle farms. No epidemiological links were found among the 12 infected premises. A questionnaire, based on the EFSA risk assessment, was used to assess the most likely route of introduction into each affected farm. Water supply for animals was the route with the highest score in 41.8% of the cases
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