FRIBS - Intermediate Energies Tagged Radioactive Ion Beams
The study of nuclei far from the valley of stability represents an important opportunity to improve the present knowledge on nuclear systems. These research activities are strictly connected with the availability of such exotic nuclei, the Radioactive Ion Beams (RIB), produced mainly through two methods: the Isotope Separation On Line (ISOL) and the Projectile recoil Fragmentation (In-Flight). This latter technique relies on the forward focusing of products in peripheral nuclear reactions and on the selection, in flight, by electromagnetic devices, of the different produced species. At present only few facilities produce RIBs at intermediate energy, motivating the development of the FRIBs (In Flight Radioactive Ions Beams) project at the Laboratori Nazionali del Sud (LNS) in Catania (fig. 1). The possibility of using the produced RIBs as secondary beams in nuclear physics experiments by applying the tagging technique, i.e. the identification, event-by-event, in charge, mass and energy of each ion of the RIBs cocktail selected by the fragment separator, before it interacts with the secondary target, has been demonstrated.
A first example of application of beams delivered by FRIBs is the DIPROTON Experiment where two-proton decay from 18Ne excited states has been studied by complete kinematical reconstruction of the decay products. The 18Ne nucleus has been produced as a radioactive beam by 20Ne projectile fragmentation at 45 AMeV on a 9Be target, and then excited via Coulomb excitation on a Pb target. The obtained results (see Activity report pag 115) unambiguously show that the 6.15 MeV 18Ne state two-proton decay proceeds through 2He emission (31%) and democratic or virtual sequential decay (69%).
G. Raciti, E. Rapisarda, M. De Napoli, F. Amorini [INFN-LNS], L. Calabretta [INFN-LNS], G. Cardella, G. Cosentino [INFN-LNS], C. Sfienti
Activity report pag 115