High precision position measurements at high counting rates with drift chambers and multi-hit electronics

11 pages, 7 figure

Virtual coupling potential for elastic scattering of 10,11^{10,11}Be on proton and carbon targets

International audienceThe 10;11Be(p,p) and (12C, 12C) reactions were analyzed to determine the in uence of the weak binding energies of exotic nuclei on their interaction potential. The elastic cross sections were measured at GANIL in inverse kinematics using radioactive 10;11Be beams produced at energies of 39:1 A and 38:4A MeV. The elastic proton scattering data were analyzed within the framework of the microscopic Jeukenne-Lejeune-Mahaux (JLM) nucleon-nucleus potential. The angular distributions are found to be best reproduced by reducing the real part of the microscopic optical potential, as a consequence of the coupling to the continuum. These effects modify deeply the elastic potential. Including the Virtual Coupling Potential (VCP), we show the ability of the general optical potentials to reproduce the data for scattering of unstable nuclei, using realistic densities. Finally, the concepts needed to develop a more general and microscopic approach of the VCP are discussed

Coupling effects in the elastic scattering of 6^{6}He on 12^{12}C

To study the effect of the weak binding energy on the interaction potential between a light exotic nucleus and a target, elastic scattering of 6He at 38.3 MeV/nucleon on a 12C target was measured at Grand Accélérateur National d'Ions Lourds (GANIL). The 6He beam was produced by fragmentation. The detection of the scattered particles was performed by the GANIL spectrometer. The energy resolution was good enough to separate elastic from inelastic scattering contributions. The measured elastic data have been analyzed within the optical model, with the real part of the optical potential calculated in the double-folding model using a realistic density-dependent nucleon-nucleon interaction and the imaginary part taken in the conventional Woods-Saxon (WS) form. A failure of the "bare" real folded potential to reproduce the measured angular distribution over the whole angular range suggests quite a strong coupling of the higher-order breakup channels to the elastic channel. To estimate the strength of the breakup effects, a complex surface potential with a repulsive real part (designed to simulate the polarization effects caused by the projectile breakup) was added to the real folded and imaginary WS potentials. A realistic estimate of the polarization potential caused by the breakup of the weakly bound 6He was made based on a parallel study of 6He+12C and 6Li+12C optical potentials at about the same energies

Charge-exchange reaction with light neutron-rich beams

The charge exchange reaction p(6He, 6Li) was studied in reverse kinematics with a secondary 6He beam at 41.6 MeV/nucleo

Étude de la diffusion élastique et de la réaction d’échange de charge (p,n) avec des faisceaux exotiques légers riches en neutrons

We have measured at GANIL, with the high resolution spectrometer SPEG, the elastic scattering of several neutron rich secondary beams (6He, 10Be and 11Be) on a polypropylene target and the charge exchange reaction p(6He, 6Li)n. These exotic beams were produced by nuclear fragmentation and re-focalized with the SISSI device (superconducting solenoids). The signature of a halo structure in these nuclei has been analysed. Special attention has been paid to several aspects of the associated calculations namely, the proton and neutron density distributions and the small binding energy for the last nucleons in these exotic nuclei. Break-up mechanisms are seen to play an important role in these nucleiNous avons mesuré au GANIL avec le spectromètre à haute résolution SPEG, la diffusion élastique de différents faisceaux secondaires riches en neutrons (6He, 10Be et 11Be) sur une cible de polypropylène, ainsi que la réaction d'échange de charge p(6He, 6Li)n. Ces faisceaux secondaires ont été produits par fragmentation nucléaire et relocalisé par le système de solénoïdes supraconducteurs SISSI. La signature d'une structure à halo dans ces noyaux est analysée dans ce travail. Une attention particulière a été apportée à certains aspects des calculs, en particulier en ce qui concerne les distributions de densité de protons et de neutrons et les faibles énergies de liaison pour les derniers nucléons de ces noyaux. Il a été mis en évidence l'importance des mécanismes de cassure pour ces noyaux exotiques

Reactions induced beyond the dripline at low energy by secondary beams

International audienceReactions induced on protons at low incident energy (3.5 MeV/n) were measured with a $^{8}$He beam accelerated by Spiral at Ganil. The particles were detected in the active target Maya, filled with $C_4$$H_10$ gas. The beam was stopped in the detector, so energies from incident beam energy down to detector threshold were covered. Proton elastic scattering, one neutron pick-up (p, d) and (p, t) reactions were observed. In the (p, d) reaction very high cross-sections of the order of 1barn were observed, that could be reproduced using a direct reaction formalism. This is the first time that this strong increase of transfer reaction cross-sections at very low energy predicted for loosely bound systems was observed. Spectroscopic factors are in agreement with a simple shell model configuration. No evidence for a low lying excited state in $^{7}$He was found