6,218 research outputs found

    Identifying structures in the continuum: Application to 16^{16}Be

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    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 9^9Be in a four-body continuum-discretized coupled-channels framework

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    We investigate the elastic scattering of 9^9Be on 208^{208}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 9^9Be 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

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    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.

    Description of the 11^{11}Li(p,d)10(p,d){^{10}}Li transfer reaction using structure overlaps from a full three-body model

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    Recent data on the differential angular distribution for the transfer reaction 11^{11}Li(p,d)10^{10}Li at E/A=5.7E/A=5.7 MeV in inverse kinematics are analysed within the DWBA reaction framework, using the overlap functions calculated within a three-body model of 11^{11}Li. The weight of the different 10^{10}Li configurations in the system's ground state is obtained from the structure calculations unambiguously. The effect of the 9^{9}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 p1/2p_{1/2} wave in the 11^{11}Li ground-state wave function. Among the considered models, the best agreement with the data is obtained when the 11^{11}Li ground state contains a \sim31\% of p1/2p_{1/2} wave in the nn-9^9Li subsystem. Although this model takes into account explicitly the splitting of the 1+1^+ and 2+2^+ resonances due to the coupling of the p1/2p_{1/2} wave to the 3/23/2^- spin of the core, a similar degree of agreement can be achieved with a model in which the 9^{9}Li spin is ignored, provided that it contains a similar p-wave content.Comment: 8 pages, 3 figures. Final versio

    Linking structure and dynamics in (p,pn)(p,pn) reactions with Borromean nuclei: the 11^{11}Li(p,pn)10(p,pn){^{10}}Li case

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    One-neutron removal (p,pn)(p,pn) 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 11^{11}Li three-body models, it is found that the 11^{11}Li(p,pn)10(p,pn){^{10}}Li relative energy spectrum is very sensitive to the position of the p1/2p_{1/2} and s1/2s_{1/2} states in 10^{10}Li and to the partial wave content of these configurations within the 11^{11}Li ground-state wave function. The possible presence of a low-lying d5/2d_{5/2} resonance is discussed. The coupling of the single particle configurations with the non-zero spin of the 9^{9}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 11^{11}Li model that incorporates the actual spin of the core and contains \sim31\% of p1/2p_{1/2}-wave content in the nn-9^9Li subsystem, in accord with our previous findings for the 11^{11}Li(p,d)10^{10}Li transfer reaction, and a near-threshold virtual state.Comment: 7 pages, 4 figures, submitted to PL

    Transportation of hazardous materials via pipeline. A historical overview

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    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

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    The continuum structure of the unbound system 10^{10}Li, inferred from the 9^{9}Li(d,p)10(d,p)^{10}Li 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 N=7N=7 parity inversion beyond the neutron dripline as well as the splitting of the well-known low-lying pp-wave resonance. Furthermore, they provide indirect evidence that most of the =2\ell=2 single-particle strength, including possible d5/2d_{5/2} resonances, lies at relatively high excitations energies.Comment: accepted for publication in Physics Letters

    Two-nucleon emitters within a pseudostate method: The case of 6^6Be and 16^{16}Be

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    Background: Since the first experimental observation, two-nucleon radioactivity has gained renewed attention over the past fifteen years. The 6^6Be system is the lightest two-proton ground-state emitter, while 16^{16}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 6^6Be and 16^{16}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 6^6Be and 16^{16}Be ground-state wave functions. These resonances are approximated as a stable PS around the known two-nucleon separation energy. Effective core-NN potentials, constrained by the available experimental information on the binary subsystems 5^5Li and 15^{15}Be, are employed in the calculations. Results: The ground state of 16^{16}Be is found to present a strong dineutron configuration, with the valence neutrons occupying mostly an l=2l=2 state relative to the core. The results are consistent with previous RR-matrix calculations for the actual continuum. The case of 6^6Be shows a clear symmetry with respect to its mirror partner, the two-neutron halo 6^6He: The diproton configuration is dominant, and the valence protons occupy an l=1l=1 orbit. Conclusions: The PS method is found to be a suitable tool in describing the properties of unbound core+N+N\text{core}+N+N ground states. For both 16^{16}Be and 6^6Be, 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 17^{17}Ne formation within a full three-body model

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    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 15O(,)19Ne^{15}\text{O}(\alpha,\gamma){^{19}\text{Ne}} and the two-proton capture reaction 15O(2p,)17Ne^{15}\text{O}(2p,\gamma){^{17}\text{Ne}} is expected. Purpose: Determine the three-body radiative capture reaction rate for 17Ne{^{17}\text{Ne}} formation including sequential and direct, resonant and non-resonant contributions on an equal footing. Method: Two different discretization methods have been applied to generate 17^{17}Ne states in a full three-body model: the analytical transformed harmonic oscillator method and the hyperspherical adiabatic expansion method. The binary pp--15^{15}O interaction has been adjusted to reproduce the known spectrum of the unbound 16^{16}F nucleus. The dominant E1E1 contributions to the 15O(2p,)17Ne^{15}\text{O}(2p,\gamma){^{17}\text{Ne}} reaction rate have been calculated from the inverse photodissociation process. Results: Three-body calculations provide a reliable description of 17^{17}Ne states. The agreement with the available experimental data on 17^{17}Ne is discussed. It is shown that the 15O(2p,)17Ne^{15}\text{O}(2p,\gamma){^{17}\text{Ne}} 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).

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    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