Asymmetry parameter for nonmesonic hypernuclear decay

We give general expressions for the vector asymmetry in the angular distribution of protons in the nonmesonic weak decay of polarized hypernuclei. From these we derive an explicit expression for the calculation of the asymmetry parameter, aΛ, which is applicable to the specific cases of ⁵ΛHe and ¹²ΛC described within the extreme shell model. In contrast to the approximate formula widely used in the literature, it includes the effects of three-body kinematics in the final states of the decay and correctly treats the contribution of transitions originating from single-proton states beyond the s-shell. This expression is then used for the corresponding numerical computation of aΛ within several one-meson-exchange models. Besides the strictly local approximation usually adopted for the transition potential, we also consider the addition of the first-order nonlocality terms. We find values for aΛ ranging from -0.62 to -0.24, in qualitative agreement with other theoretical estimates but in contradiction with some recent experimental determinations.Facultad de Ciencias Exacta

Relativistic RPA for Isobaric Analogue and Gamow-Teller Resonances in Closed Shell Nuclei

We perform a self-consistent relativistic RPA calculation for the isobaric analogue and Gamow-Teller resonances based on relativistic mean field theory results for the ground states of 48Ca, 90Zr and 208Pb. We use the parameter set NL1 for the σ, ω and ρ mesons, and experimental values for the pion and nucleon. An extra parameter, related to the intensity of the contact term in the pion-exchange interaction, is crucial to reproduce the latter resonances.Facultad de Ciencias Exacta

Nonmesonic weak decay spectra of 4/ʌ He

To comprehend the recent Brookhaven National Laboratory experiment E788 on He Λ 4, we have outlined a simple theoretical framework, based on the independent-particle shell model, for the one-nucleon-induced nonmesonic weak decay spectra. Basically, the shapes of all the spectra are 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 (Λ π ≈ 0.7 GeV, Λ K ≈ 0.9 GeV ), is able to account simultaneously for the available experimental data related to Γ p and Γ n for H Λ 4, He Λ 4, and He Λ 5.Facultad de Ciencias ExactasFacultad de Ciencias Astronómicas y Geofísica

Pesquisas e avanços tecnológicos no manejo sustentável de açaizais nativos no estuário amazônico.

Apresentar o histórico da pesquisa para a melhoria do sistema tradicional de manejo de açaizais nativos do estuário amazônico e os avanços tecnológicos alcançados com o incentivo à utilização das boas práticas de manejo para a sustentabilidade socioambiental da atividade e a perenidade da produção de frutos da espécie na regiã

Transition amplitudes for the nonmesonic hypernuclear decay

We give general expressions for the two-body decomposition of the transition amplitudes for the nonmesonic decay of Lambda-hypernuclei within a finite-nucleus shell-model approach

Asymmetry parameter for nonmesonic hypernuclear decay

We derive general explicit expressions for a shell-model calculation of the intrinsic asymmetry parameter, $a_\Lambda$, in nonmesonic weak hypernuclear decay. They include the effects of three-body kinematics in the final states of the decay and correctly treat the contribution of transitions originating from single-proton states beyond the s-shell. The expressions are particularized to the cases of $^5_\Lambda$He and $^{12}_\Lambda$C and used for the calculation of $a_\Lambda$ in several one-meson-exchange models. Besides the strictly local approximation usually adopted for the transition potential, we also consider the addition of the first-order nonlocality terms. We find values for $a_\Lambda$ ranging from -0.62 to -0.24, in qualitative agreement with other theoretical estimates but in contradiction with some recent experimental determinations

A MODEL OF THE DEUTERON BASED ON A BREIT TYPE EQUATION

A relativistic treatment of the deuteron and its observables based on a two-body Dirac (Breit) equation, with phenomenological interactions, associated to one-boson exchanges with cutoff masses, is presented. The 16-component wave function for the deuteron (J(pi) = 1+) solution contains four independent radial functions which obey a system of four coupled differential equations of first order. This radial system is numerically integrated, from infinity to the origin, by fixing the value of the deuteron binding energy and using appropriate boundary conditions at infinity. Specific examples of mixtures containing scalar, pseudoscalar and vector like terms are discussed in some detail and several observables of the deuteron are calculated. Our treatment differs from more conventional ones in that nonrelativistic reductions of the order c-2 are not used

Inventário florestal do Núcleo de Apoio e Transferência de Tecnologia da unidade da Embrapa Amazônia Oriental: relatório de atividades.

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