Nonmesonic weak decay spectra of He-4(Lambda)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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 decay dynamics 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 bole states are treated as stationary, while in version IPSM-b the deep-hole ones are considered to be quasi-stationary and are described by Breit-Wigner distributions.

Kinetic energy sum spectra in nonmesonic weak decay of hypernuclei

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nonmesonic weak decay of Λ-hypernuclei within independent-particle shell-model

After a short introduction to the nonmesonic weak decay (NMWD) ΛN→nN of Λ-hypernuclei we discuss the long-standing puzzle on the ratio Γn/Γp, and some recent experimental evidences that signalized towards its final solution. Two versions of the Independent-Particle-Shell-Model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account, and (b) IPSM-b, where the highly excited hole states are considered to be quasi-stationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. We evaluate the coincidence spectra in Λ 4He, Λ 5He, Λ 12C, Λ 16O, and Λ 28Si, as a function of the sum of kinetic energies EnN=En+EN for N=n, p. The recent Brookhaven National Laboratory experiment E788 on Λ 4He, is interpreted within the IPSM. We found that the shapes of all the spectra are basically tailored by the kinematics of the corresponding phase space, depending very weakly on the dynamics, which is gauged here by the one-meson-exchange- potential. In spite of the straightforwardness of the approach a good agreement with data is achieved. This might be an indication that the final-state- interactions and the two-nucleon induced processes are not very important in the decay of this hypernucleus. We have also found that the π+K exchange potential with soft vertex-form-factor cutoffs (Λπ≈0. 7GeV, ΛK≈0.9GeV), is able to account simultaneously for the available experimental data related to Γp and Γn for Λ 4H, and Λ 5He. © 2010 American Institute of Physics.

One-nucleon-induced nonmesonic hypernuclear decay in laboratory coordinates

We present a formalism for the computation of one-nucleon-induced nonmesonic weak hypernuclear decay rates in laboratory coordinates, within an independent-particle shell model framework, with a view to its generalization to the case of two-nucleon-induced transitions. © 2013 AIP Publishing LLC.

Crescimento in vitro e aclimatização de Cattleya loddigesii Lindley (Orchidaceae) com carvão ativado sob dois espectros luminosos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Scaling in few-body nuclear physics

The nuclear matter calculations with realistic nucleon-nucleon potentials present a general scaling between the nucleon-nucleus binding energy, the corresponding saturation density, and the triton binding energy. The Thomas-Efimov three-body effect implies in correlations among low-energy few-body and many-body observables. It is also well known that, by varying the short-range repulsion, keeping the two-nucleon information (deuteron and scattering) fixed, the four-nucleon and three-nucleon binding energies lie on a very narrow band known as a Tjon line. By looking for a universal scaling function connecting the proper scales of the few-body system with those of the many-body system, we suggest that the general nucleus-nucleon scaling mechanism is a manifestation of a universal few-body effect.

NUCLEAR DENSITIES AND THE STATISTICS OF NUCLEONIC CONSTITUENTS

In the quark model of the nucleon, the Fermi statistics of the elementary constituents can influence significantly the properties of multinucleon bound systems. In the Skyrme model, on the other hand, the basic quanta are bosons, so that qualitatively different statistics effects can be expected a priori. In order to illustrate this point, we construct schematic one-dimensional quark and soliton models which yield fermionic nucleons with identical baryon densities. We then compare the baryon densities of a two-nucleon bound state in both models. Whereas in the quark model the Pauli principle for quarks leads to a depletion of the density in the central region of the nucleus, the soliton model predicts a slight increase of the density in that region, due to the bosonic statistics of the meson-field quanta.

Tjon Lines and Scaling Limit in Four-Body Systems

The fixed-slope correlation between tetramer and trimer binding energies, observed by Tjon in the context of nuclear physics, is mainly a manifestation of the dominance of the two-nucleon force in the nuclear potential, which makes the four-body scale on the order of the three-body one. In a more general four-boson case, the correlation between tetramer and trimer binding energies has a non-fixed slope, which expresses the dependence on the new scale. The associated scaling function generates a family of Tjon lines. This conclusion relies on a recent study with weakly-bound four identical bosons, within a renormalized zero-range Faddeev-Yakubovsky formalism. © 2012 Springer-Verlag.

Avaliação do laser de baixa intensidade na regeneração de cartilagem articular do joelho de coelhos submetidos à trocleoplastia

Pós-graduação em Cirurgia Veterinária - FCAV

Comparison of Nonmesonic Hypernuclear Decay Rates Computed in Laboratory and Center-of-Mass Coordinates

In this work we compute the one-nucleon-induced nonmesonic hypernuclear decay rates of He-5(Lambda), C-12(Lambda) and C-13(Lambda) using a formalism based on the independent particle shell model in terms of laboratory coordinates. To ascertain the correctness and precision of the method, these results are compared with those obtained using a formalism in terms of center-of-mass coordinates, which has been previously reported in the literature. The formalism in terms of laboratory coordinates will be useful in the shell-model approach to two-nucleon-induced transitions.

Classification of intact açai (Euterpe oleracea Mart.) and jucara (Euterpe edulis Mart) fruits based on dry matter content by means of near infrared spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigation of the two-photon absorption cross-section in perylene tetracarboxylic derivatives: Nonlinear spectra and molecular structure

We investigated the 2PA absorption spectrum of a family of perylene tetracarboxylic derivatives ( PTCDs): bis( benzimidazo) perylene ( AzoPTCD), bis( benzimidazo) thioperylene ( Monothio BZP), n-pentylimidobenzimidazoperylene ( PazoPTCD), and bis( n-butylimido) perylene ( BuPTCD). These compounds present extremely high two-photon absorption, which makes them attractive for applications in photonics devices. The two-photon absorption cross-section spectra of perylene derivatives obtained via Z-scan technique were fitted by means of a sum-over-states ( SOS) model, which described with accuracy the different regions of the 2PA cross-section spectra. Frontier molecular orbital calculations show that all molecules present similar features, indicating that nonlinear optical properties in PTCDs are mainly determined by the central portion of the molecule, with minimal effect from the lateral side groups. In general, our results pointed out that the differences in the 2PA cross-sections among the compounds are mainly due to the nonlinearity resonance enhancement.

Nonmesonic weak decay dynamics from proton spectra of Lambda-hypernuclei

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)