Close-coupling calculations of positronium formation in positron-helium scattering

Positronium (Ps) formation in positron-helium scattering has been investigated in different partial waves at medium energies including the Ore gap region using the close-coupling approximation with realistic wavefunctions for the following states: He(1s1s), He(1s2s), He(1s2p), He(1s3s), He(1s3p), Ps(ls), Ps(2s), Ps(2p). Calculations are reported of rearrangement cross sections to Ps(ls), Ps(2s) and Ps(2p) states for incident positron energies up to 200 eV. The present partial cross sections are in good agreement with experimental results and a variational calculation in the Ore gap region.

Kinetics of Ag-rich precipitates formation in Cu-Al-Ag alloys

The kinetics of Ag-rich precipitates formation in the Cu-2 wt.% Al alloy with additions of 2, 4, 6, 8, 10 and 12 wt.% Ag was studied using microhardness changes with temperature and time, differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that an increase in the Ag content decreases the activation energy for Ag-rich precipitates formation, and that it is possible to estimate the values of the diffusion and nucleation activation energies for the Ag precipitates. (C) 2004 Elsevier B.V. All rights reserved.

THE EFFECT OF POSITRONIUM FORMATION IN POSITRON ALKALI-ATOM SCATTERING

We study e+-Na, e+-K, and e+-Rb scattering using the close coupling approach in the static and coupled static expansion schemes. We calculate partial wave elastic scattering phase shifts and total elastic and Ps formation cross sections up to an incident positron energy of 100 eV. The effect of the positronium formation channel on the elastic channel is found to be strong in all cases up to an incident positron energy of 10 eV. We also make an estimate of the total cross section which exhibits a minimum as a function of energy at low energies.

Differential cross sections for target excitation and positronium formation in positron-helium scattering

Positronium formation and target excitation in positron-helium scattering have been investigated using the close-coupling approximation with realistic wave functions for the positronium and helium atoms. The following eight states have been used in the close-coupling scheme: He(1s1s), He(1s2(1)s), He(1s2(1)p), He(1s3(1)s), He(1s3(1)p), Ps(1s), Ps(2s), and Ps(2p), where Ps stands for the positronium atom. Calculations are reported of differential cross sections for elastic scatering,, inelastic target excitation to He(1s2(1)s) and He(1s2(1)p) slates, and rearrangement transition to Ps(1s), Ps(2s), and Ps(2p) states for incident positron energies between 40 and 200 eV. The coincidence parameters for the transition to the He(1s2(1)p) state of helium are also reported and briefly discussed. [S1050-2947(98)05101-4].

Molecular Dynamics simulations of track formation at different ensembles

A series of Molecular Dynamics simulations of thermal spikes has been run in zircon. For two different ensembles: microcanonical one and a combination of microcanonical one acting on the simulation core with Langevin one on the side walls of simulation. Depending on the used ensemble, different track-formation threshold energies were found. When the combined ensemble is carried out, the total energy of the simulations varies with the temperature which can influence how annealing fission-track models should deal with the lattice recovery. A fission-track annealing model is tested with the simulation results. © 2012 Elsevier Ltd. All rights reserved.

Molecular properties of the PCO radical: heat of formation and the isomerization pathways

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)