XXXIII BRAZILIAN WORKSHOP ON NUCLEAR PHYSICS
1351(2011); http://dx.doi.org/10.1063/1.3608930View Description Hide Description
A finite many‐body system of interacting identical bosons in an effectively one‐dimensional, ring‐shaped external potential array with periodic boundary conditions is treated in terms of numerical shell‐model‐like matrix diagonalization within a truncated subspace. Ground state energies and one‐body density matrices are studied as a function of the external potential parameters. Features associated to the phase transition to the Mott insulator regime in the thermodynamic limit are identified in the finite systems. Inertial parameters obtained in a cranking calculation are discussed in terms of the onset superfluidity in the system.
1351(2011); http://dx.doi.org/10.1063/1.3608931View Description Hide Description
This contribution contains six sections, namely:
1. from QCD to chiral perturbation theory ‐ QCD is widely accepted as the theory of strong interactions, but direct applications to low‐energy hadronic processes are difficult. In this regime, the light quarks u and d prevail, and one can employ a rigorously equivalent effective theory, known a chiral perturbation theory, based on hadronic degrees of freedom.
2. strong vacuum and the pion ‐ Chiral symmetry is not exact in the real world. Nevertheless, the absence of of parity multiplets and the smallness of the pion mass suggest that it is a good approximate symmetry, realized in the Nambu‐Goldstone mode. Its ground state, the vacuum, is filled with a condensate, made of quark‐antiquark pairs. In sections 1–3, instances are presented of observables strongly influenced by the QCD vacuum.
3. nuclear forces ‐ In the last few years, chiral perturbation theory has produced a very reliable picture of both two‐ and three‐nucleon forces. In particular, the important isospin independent central potential is well understood and known to be dominated by the scalar form factor of the nucleon, a function that describes the disturbance it produces over the vacuum.
4. nucleon scalar form factor ‐ The spatial integration of the nucleon scalar form factor gives rise to the nucleon σ‐term. The value of this quantity can be extracted from experiment and the empirical value accepted presently is A simple model, based on the idea that the pion cloud of the nucleon is constructed at the expenses of the surrounding condensate, produces a in the range 43–49 MeV, with no free parameters.
5. scalar radius of the pion ‐ The value of this radius can be extracted from pion‐pion scattering data and the most reliable estimate is The extension of the model described in section 4 to the pion gives rise to a picture in which it is embedded into the condensate. As one moves towards its center, the condensate is gradually replaced by a mesonic cloud. When this process is completed, a phase transition occurs, at a distance A version of the model, including scalar resonances, yields
6. conclusion ‐ The QCD vacuum is an active component of low‐energy hadronic processes, essential to a consistent description of Nuclear Physics.
1351(2011); http://dx.doi.org/10.1063/1.3608932View Description Hide Description
The four‐body continuum‐discretized coupled‐channels approach using a continuum‐bins scheme of discretization for three‐body projectiles, that has been recently developed, is presented. The formalism is discussed and applied to reactions induced by the Borromean nucleus on different targets ( and ), with special emphasis on the role of the Coulomb couplings.
1351(2011); http://dx.doi.org/10.1063/1.3608933View Description Hide Description
Both the Fermi breakup (FBM) and the Statistical Multifragmentation (SMM) models provide prescriptions for calculating mass and charge distributions and multiplicities of the fragments emitted in the breakup of an excited nuclear system. Although they are usually formulated in different terms and applied in very different regions of mass and excitation energy, they are essentially one and the same model. We make this close relationship explicit and compare results of calculations using the FBM in use today and the one proposed here. We then show how the FBM/SMM is related to the usual compound nucleus evaporation model and how the two might be unified and extended to provide a comprehensive description of statistical nuclear decay.
1351(2011); http://dx.doi.org/10.1063/1.3608934View Description Hide Description
Even with the important advances of the last decade, charmed meson decays are still poorly understood theoretically. It is not clear, for instance, why the kappa scalar resonance is responsible for 70% of the fit in decay, as observed by the E791 (2002). Usual models for do not treat properly the weak vertex. Moreover, they also consider the final state interactions in the quasi two‐body approximation, where one of the pions acts as a spectator of the Kπ interaction. As an input to treating D decay, the scattering amplitude was calculated by means of a ChPT lagrangian and the kappa was found as a dynamically generated pole. This work aims to quantify the relevance of 3‐body final state interaction for the whole decay. With this purpose in mind, we calculate three classes of diagrams in the perturbative series and discuss their relative importance.
1351(2011); http://dx.doi.org/10.1063/1.3608935View Description Hide Description
In a previous work , we have calculated the one‐proton emission rate of nuclei near the proton drip line, by using an analytical barrier parametrization. The calculation is based on the WKB‐approximation and half‐lives are obtained in good agreement with the existing experimental data for one‐proton emitters. Motivated by these results, in present work, we have eliminated the artificial barrier parametrization previously used, constructing a realistic barrier composed by the superposition of a nuclear Wood‐Saxon potential form plus the coulomb and centrifugal barrier. The purpose here is to see if the simple WKB‐calculation is still able to reproduce recent observed experimental results for two‐proton emission from This decay mode has been observed by Miernik et al. , reporting the proton energy distribution and half‐life energy dependence for simultaneous 2p‐emission. For theoretical determination of the half‐life and these energy distributions we evoked a statistical assumption of a pioneering Goldansky’s work  for discussing simultaneous two‐proton emission. We have shown that our calculation reproduce in quite good agreement the energy distribution and is also able to offer good half‐life result with an appropriated composition of involved values of the angular momentum decay.
1351(2011); http://dx.doi.org/10.1063/1.3608936View Description Hide Description
Having its origin in a successful mapping technique, the Fock‐Tani formalism, has produced a corrected model ( model), which retains the basic aspects of the predictions with the inclusion of bound‐state corrections. In high energy collisions many new mesons have been discovered in particular the enigmatic and The model is applied for mesons decay. The amplitude and its respective decay rates are evaluated.
1351(2011); http://dx.doi.org/10.1063/1.3608937View Description Hide Description
A stochastic variational method is applied to calculate the binding energies and root‐mean‐square radii of 2, 3 and 4 α particles using an S‐wave Ali‐Bodmer potential. The results agree with other calculations. We discuss the application of the present method to study the universality in weakly‐bound three and four‐body systems in the context of ultracold atomic traps.
1351(2011); http://dx.doi.org/10.1063/1.3608938View Description Hide Description
The structure is investigated in the nuclei and The ground state bands of the and systems were calculated with a local cluster‐core potential, where only the radial parameter is variable. The calculated spectra give a good general description of the experimental and levels. The reduced α‐widths, B(E2) transition rates and rms intercluster separations are determined for the ground state bands of the two nuclei. The calculations reproduce correctly the order of magnitude of the experimental B(E2) values of without the use of effective charges and indicate that the first members of the ground state band of present a stronger α‐cluster character. Predictions concerning a negative parity band of the system are also shown.
1351(2011); http://dx.doi.org/10.1063/1.3608939View Description Hide Description
In the present work we determine the equation of state of delta‐resonance‐rich stellar matter and discuss the effects of the baryon‐meson coupling constants on the delta population in the stellar medium. We extended the non‐linear Walecka (NLW) model to accommodate in the context of the relativistic mean field approximation the Rarita‐Schwinger field for the spin 3/2 resonances.
1351(2011); http://dx.doi.org/10.1063/1.3608940View Description Hide Description
The two‐proton decay of resonances is investigated in a statistical calculation framework, both for ground and first excited states. The phenomenological approach previously used to determine the parameters of the ground state was applied here to evaluate the energy peak and width of the excited resonant states. We also calculate the branching ratios of different resonant states decay through the simultaneous and sequential emissions.
1351(2011); http://dx.doi.org/10.1063/1.3608941View Description Hide Description
In the present work we evaluate the process using the BCS, PBCS, QRPA and PQRPA models as nuclear models. We show the behavior of the muon capture rates as a function of the t‐parameter, strength of the pp‐channel in the residual δ‐interaction. The obtained results for the muon capture rates show that the projection procedure is important for medium mass nuclei as
1351(2011); http://dx.doi.org/10.1063/1.3608942View Description Hide Description
Valuable information on exotic nuclei far from stability has been obtained at the Legnaro National Laboratory with the high efficiency gamma‐ray spectrometer CLARA, coupled to the magnetic spectrometer PRISMA, or the AGATA Demonstrator. Near a new region of deformation is observed due to changes in the shell structure of neutron‐rich Cr and Fe isotopes. Recent experimental and theoretical results will be shown and discussed as well as the expected experimental conditions at the planned future facilities for radioactive ion beams and for high‐intensity stable beams.
1351(2011); http://dx.doi.org/10.1063/1.3608943View Description Hide Description
The first accelerating structures of the São Paulo microtron accelerator presently deliver a continuous‐wave 1.9 MeV electron beam, which can be used in atomic physics studies. An energy‐analyzed beam line with focalization magnets, irradiation chamber, movable target system and Faraday cup was built. Here, we will describe the preliminary results of two experiments. In the first one, upper limits on K‐shell ionization cross sections of Pd and Au atoms by electron impact were obtained. To this end, thin targets of these elements were irradiated with the beam impinging at 45° while the emitted Kα x‐rays were recorded with an HPGe x‐ray detector positioned at 90° with respect to the beam direction. The other experiment was the measurement of the bremsstrahlung energy spectra produced by the aforementioned targets in the same geometrical configuration but using an HPGe γ‐ray detector instead. The latter experiment enabled the determination of the electron‐beam energy as 1.909(5) MeV.
1351(2011); http://dx.doi.org/10.1063/1.3608944View Description Hide Description
We present the results of the transfer reaction, measured at the RIBRAS facility. It was performed in inverse kinematics using a thick polyethylene target. The complete excitation function was measured between which includes the Gamow peak energy region. The excitation function was reproduced with the R‐matrix theory.
1351(2011); http://dx.doi.org/10.1063/1.3608945View Description Hide Description
The reaction was used to investigate alpha resonant states in up to 15 MeV of excitation. The reaction was measured at a bombarding energy of 25.5 MeV employing the São Paulo Pelletron‐Enge‐Spectrograph facility and the nuclear emulsion detection technique. An energy resolution of 50 keV was obtained. Several narrow alpha resonant states not previously measured were detected, in particular the one at the threshold populated by an transfer, revealing a component for the cluster state candidate at this threshold. Experimental angular distributions are presented in comparison with DWBA predictions.
1351(2011); http://dx.doi.org/10.1063/1.3608946View Description Hide Description
In this work we present preliminary results of the continuum discretized coupled channel (CDCC) calculation for the system at energies near the Coulomb barrier. In the three‐body cluster model of the proton halo projectile the São Paulo potential was used as a bare potential. We study the relative relevance of the Coulomb and nuclear breakups and its interference. The importance of each multipolarity of the interaction potential expansion is studied in detail. The polarization potentials are also generated and its energy dependence is studied. The effect of the continuum‐continuum couplings for this light system is analyzed. The results for this system are compared with the previous ones for the system, as the charge of the target is smaller.
1351(2011); http://dx.doi.org/10.1063/1.3608947View Description Hide Description
In this work, the half life of the β decay of was measured by following the activity of 32 samples of 50 μg each after they were irradiated in the IEA‐R1 reactor of IPEN‐CNEN/SP. The results were then fitted using a non‐paralizable dead time correction to the regular exponential decay and the individual half‐life values obtained were then analyzed using different statistical methods (Weighted Average, Normalized Residuals and Rajeval Technique), resulting in a value of 3.733(4) min. The obtained result is somewhat smaller than tabulated one but the difference does not surpass two standard deviations.