Exotic beams

Beams of radioactive nuclei are produced by two different techniques based on the acceleration of radioactive nuclei produced in thick targets using proton induced spallation, and on the fragmentation of intermediate or high energy heavy ion beams. The first method implies the use of an isotope separator for selecting the nuclei of interest, and in the second method a magnetic selection is performed with a recoil spectrometer, and associated to a beam purification step using a degrader placed in an intermediate focal plane of the spectrometer. The first series of experiments concern the cross-section measurements of the astrophysical reaction 13N(p,γ)14O at very low energy. The second series of experiments concern the determination of the strong interaction radius for exotic nuclei from total reaction cross-section measurements, and the study of neutron halos in very neutron rich light isotopes. (R.P.) 58 refs., 26 figs