DISCUSSION DU MÉCANISME DES RÉACTIONS DE TRANSFERT TRÈS INÉLASTIQUE

Sous ce terme sont englobées les réactions qui mettent en jeu des échanges importants de matière et d'énergie, sans aboutir à la fusion complète des partenaires. Lorsque le projectile utilisé est relativement léger (A < 40), on observe des réactions de transfert très inélastique dont les distributions angulaires dans le système du centre de masse correspondent à un produit léger émis préférentiellement vers l'avant, et pour des projectiles plus lourds, des réactions dites de quasi-fission dont les distributions angulaires présentent un maximum proche de l'angle d'effleurement. Les modèles théoriques utilisés pour rendre compte de ces réactions supposent l'intervention de forces de frottement (viscosité) entre les noyaux. Ces forces sont responsables des grandes pertes d'énergie cinétique observées. Le transfert de matière est traité comme un processus de diffusion en utilisant les équations de transfert issues de la mécanique statistique

Mesure de l'énergie des ions lourds par la méthode des protons projetés

Un dispositif destiné à la mesure de l'énergie des faisceaux d'ions lourds de 3 à 6 MeV/ uma a été construit. Le principe de la méthode est de mesurer l'énergie des protons projetés à zéro degré par collision élastique des ions incidents avec les noyaux d'hydrogène d'une cible de formvar. L'incertitude calculée sur l'énergie ainsi mesurée pour les ions lourds est de + 0,45 %. Des mesures faites sur des faisceaux de 19F et 40Ca d'énergie bien connue, accélérés par un Tandem MP, ont montré un écart maximum de 0,3 % entre les énergies réelles et mesurées. Le dispositif permet de contrôler ou calibrer des méthodes plus lourdes de détermination de l'énergie des ions lourds : déviation magnétique, temps de vol. Il se prête particulièrement bien à la mesure des pertes d'énergie d'ions lourds dans des ralentisseurs solides

Stopping of energetic sulfur and bromine ions in dense hydrogen plasma

The concepts of communicative space, media sphere and public sphere are sometimes used like synonyms one of the other. However, according to us, they are three different concepts: public sphere and media sphere are two distinct spaces symbolic systems which, both, are anchored in communicative spac

HEAVY ION SECONDARY BEAMS

The possibility of producing secondary beams of radioactive nuclei is an interesting application of medium and high energy heavy ion beams. After a first attempt at CERN (1) , two experiments have been performed at GANIL, using 44 MeV/u 40Ar (2) and 65 MeV/u 180 projectiles. This paper recalls the results of the Ar experiment, and presents new data obtained with the 180 beam

G0^0 Electronics and Data Acquisition (Forward-Angle Measurements)

The G$^0$ parity-violation experiment at Jefferson Lab (Newport News, VA) is designed to determine the contribution of strange/anti-strange quark pairs to the intrinsic properties of the proton. In the forward-angle part of the experiment, the asymmetry in the cross section was measured for $\vec{e}p$ elastic scattering by counting the recoil protons corresponding to the two beam-helicity states. Due to the high accuracy required on the asymmetry, the G$^0$ experiment was based on a custom experimental setup with its own associated electronics and data acquisition (DAQ) system. Highly specialized time-encoding electronics provided time-of-flight spectra for each detector for each helicity state. More conventional electronics was used for monitoring (mainly FastBus). The time-encoding electronics and the DAQ system have been designed to handle events at a mean rate of 2 MHz per detector with low deadtime and to minimize helicity-correlated systematic errors. In this paper, we outline the general architecture and the main features of the electronics and the DAQ system dedicated to G$^0$ forward-angle measurements.Comment: 35 pages. 17 figures. This article is to be submitted to NIM section A. It has been written with Latex using \documentclass{elsart}. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment In Press (2007

Phenomenology of the Deuteron Electromagnetic Form Factors

A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the 4-momentum transfer range 0-7 fm^-1. This procedure is made possible with the advent of recent polarization measurements. The parameterizations allow a phenomenological characterization of the deuteron electromagnetic structure. They can be used to remove ambiguities in the form factors extraction from future polarization data.Comment: 18 pages (LaTeX), 2 figures Feb. 25: minor changes of content and in Table

INVESTIGATION OF THE TRANSMISSION AND STOPPING OF LIGHT IONS PASSING THROUGH A PLASMA TARGET

Transmission and energy losses of 2 MeV/u Carbon and Sulphur beams passing through a plasma target, have been extensively investigated. A hydrogen plasma ignited by an electrical discharge was coupled to the Orsay Tandem beam accelerator. Fluctuations in beam transmission have been observed and attributed to a magnetic focusing effect generated during the plasma evolution. Energy loss measurements were performed on the basis of time of flight techniques and indicate an enhanced stopping power of the plasma relative to its cold matter equivalent

A precise measurement of the deuteron elastic structure function A(Q^2)

The A(Q^2) structure function in elastic electron-deuteron scattering was measured at six momentum transfers Q^2 between 0.66 and 1.80 (GeV/c)^2 in Hall C at Jefferson Laboratory. The scattered electrons and recoil deuterons were detected in coincidence, at a fixed deuteron angle of 60.5 degrees. These new precise measurements resolve discrepancies between older sets of data. They put significant constraints on existing models of the deuteron electromagnetic structure, and on the strength of isoscalar meson exchange currents.Comment: 3 LaTeX pages plus 2 PS figure

Measurement of Tensor Polarization in Elastic Electron-Deuteron Scattering at Large Momentum Transfer

Tensor polarization observables (t20, t21 and t22) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)^2. The experiment was performed at the Jefferson Laboratory in Hall C using the electron HMS Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q^2 the deuteron charge form factors G_C and G_Q. They are in good agreement with relativistic calculations and disagree with pQCD predictions.Comment: 5 pages, 4 figures, for associated informations, see http://isnwww.in2p3.fr/hadrons/t20/t20_ang.html clarification about several topics, one figure has been had, extraction of form factors use AQ interpolation in our Q2 range onl