Exotic beams

Beams of radioactive nuclei are produced by two techniques based on the acceleration of radioactive nuclei produced in thick targets using proton induced spallation, or similar reactions, and the fragmentation of intermediate of 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. Although the intensities of such secondary beams are still low, several types of experiments have been performed, and are described in this paper. The first series of experiments concern the cross-section measurements of the astrophysical reaction 13N (p,γ)14O at very low energy, which have been made, either directly, from an accelerated 13N beam, or through the Coulomb break-up of an intermediate energy 14O beam, which gives access to the inverse reaction 14O(γ,p)13N.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, and particularly in 11Li. This last study involved inclusive experiments in which 9Li and other nuclei from 11Li fragmentation were detected, and also an exclusive experiment in which the angular distribution of neutrons was measured in coincidence with 9Li fragments from 11Li break-up. (author)