Measurements of the Delta(1232) Transition Form Factor and the Ratio sigma_n\sigma_p From Inelastic Electron-Proton and Electron-Deuteron Scattering

Measurements of inclusive electron-scattering cross sections using hydrogen and deuterium targets in the region of the Delta(1232) resonance are reported. A global fit to these new data and previous data in the resonance region is also reported for the proton. Transition form factors have been extracted from the proton cross sections for this experiment over the four-momentum transfer squared range 1.64 < Q^2 < 6.75 (GeV/c)^2 and from previous data over the range 2.41 < Q^2 < 9.82 (GeV/c)^2. The results confirm previous reports that the Delta(1232) transition form factor decreases more rapidly with Q^2 than expected from perturbative QCD. The ratio of sigma _n \sigma_p in the \Delta(1232) resonance region has been extracted from the deuteron data for this experiment in the range 1.64 < Q^2 < 3.75 (GeV/c)^2 and for a previous experiment in the range 2.4 < Q^2 < 7.9 (GeV/c)^2. A study has been made of the model dependence of these results. This ratio sigma_n\sigma_p for \Delta(1232) production is slightly less than unity, while sigma_n\sigma_p for the nonresonant cross sections is approximately 0.5, which is consistent with deep inelastic scattering results.Comment: 10 figures. 42 pages, including figures. submitted to Physical Review

A general protocol for the reconstruction of 3D atom probe data

International audienceData collected with 3D atom probes have to be carefully analysed in order to give reliable composition data precisely positioned in the probed volume. Indeed, the large analysed surfaces of 3D atom probes require the development of reconstruction methods taking into account the tip geometry. When the analysis does not take place in the close vicinity of the tip axis, the analysis direction is no longer perpendicular to the evaporated surface. The influence of this effect on the local magnification and atom positioning must be taken into account. The proposed procedure will be validated by studying the effects of calculations on a long-range-ordered phase. \textcopyright 1995

Atom probe characterization of isotropic spinodal decompositions: spatial convolutions and related bias

International audienceThe present study aims at characterizing the amplitude of chromium concentration fluctuations which occur in the spinodally decomposed ferrite phase of a duplex stainless steel. Measured amplitudes are shown to be dependent on both the value of the analysis diameter and the sampling depth as compared with the characteristic lengths of concentration fluctuations. A theoretical model has been designed in order to quantify this dependence. It takes into account axial smoothing, associated with depth sampling, and radial convolution, related to the analysed area which have been studied as a function of different analysis conditions. Optimized analysis parameters are deduced and the corresponding attenuation factor, relative to amplitude measurement, is calculated. \textcopyright 1991

Atom probe characterization of isotropic spinodal decompositions: spatial convolutions and related bias

International audienceThe present study aims at characterizing the amplitude of chromium concentration fluctuations which occur in the spinodally decomposed ferrite phase of a duplex stainless steel. Measured amplitudes are shown to be dependent on both the value of the analysis diameter and the sampling depth as compared with the characteristic lengths of concentration fluctuations. A theoretical model has been designed in order to quantify this dependence. It takes into account axial smoothing, associated with depth sampling, and radial convolution, related to the analysed area which have been studied as a function of different analysis conditions. Optimized analysis parameters are deduced and the corresponding attenuation factor, relative to amplitude measurement, is calculated. \textcopyright 1991

A general protocol for the reconstruction of 3D atom probe data

International audienceData collected with 3D atom probes have to be carefully analysed in order to give reliable composition data precisely positioned in the probed volume. Indeed, the large analysed surfaces of 3D atom probes require the development of reconstruction methods taking into account the tip geometry. When the analysis does not take place in the close vicinity of the tip axis, the analysis direction is no longer perpendicular to the evaporated surface. The influence of this effect on the local magnification and atom positioning must be taken into account. The proposed procedure will be validated by studying the effects of calculations on a long-range-ordered phase. \textcopyright 1995

Analytic treatment of charge cloud overlaps: An improvement of the tomographic atom probe efficiency

International audienceAlthough reliable position and composition data are obtained with the Tomographic Atom Probe, the procedure of position calculation by charge centroiding fails when the detector receives two or more ions with close spaced positions and the same mass-to-charge ratio. As the charge clouds of the ions overlap, they form a unique charge pattern on the multianode detector. Only one atom is represented and its position is biased. In order to estimate real positions, we have developed a correction method. The spatial distribution of charges inside a cloud issued from one impact is modelled by a Gaussian law. The particular properties of the Gaussian enable the calculation of exact positions of the two impacts of the overlapped charge patterns and charges of corresponding clouds. The calculation may be generalized for more than two overlapped clouds. The method was tested on a plane-by-plane analysis of a fully ordered Cu3Au alloy performed on a (100) pole

Analytic treatment of charge cloud overlaps: An improvement of the tomographic atom probe efficiency

International audienceAlthough reliable position and composition data are obtained with the Tomographic Atom Probe, the procedure of position calculation by charge centroiding fails when the detector receives two or more ions with close spaced positions and the same mass-to-charge ratio. As the charge clouds of the ions overlap, they form a unique charge pattern on the multianode detector. Only one atom is represented and its position is biased. In order to estimate real positions, we have developed a correction method. The spatial distribution of charges inside a cloud issued from one impact is modelled by a Gaussian law. The particular properties of the Gaussian enable the calculation of exact positions of the two impacts of the overlapped charge patterns and charges of corresponding clouds. The calculation may be generalized for more than two overlapped clouds. The method was tested on a plane-by-plane analysis of a fully ordered Cu3Au alloy performed on a (100) pole