Nuclear Structure far from Stability at LNL: From high intensity stable to radioactive nuclear beams

摘要

Future perspectives in nuclear structure rely on radioactive nuclear beams as well as on high intensity beams of stable ions. Deep-inelastic and multi-nucleon transfer reactions with stable beams of heavy elements can be used to populate yrast and non yrast states of neutron rich nuclei. Particularly powerful is here the combination of large acceptance spectrometers with highly segmented gamma-detector arrays. Such devices, eventually complemented by large coverage particle detectors, can provide the necessary channel selectivity to identify very rare signals. An example is the CLARA gamma-ray detector array coupled with the PRISMA spectrometer at the Legnaro National Laboratories (LNL). The physics aims achievable complement studies performed with current radioactive beam (RIB) facilities. With such set-up we have recently investigated the stability of the N=50 shell closure when moving towards more exotic systems. Here the comparison of the experimental data with shell model calculations seems to indicate a persistence of the N=50 shell gap down to Z=31. Future perspectives at LNL are based on an increase in intensity as well as on the availability of heavy ion species. Beams like 1 16 Xe or 208 Pb, provided by the new PIAVE injector, can be used to drive the multinucleon flux toward the most exotic regions. Moreover a new ISOL facility (SPES) dedicated to the production and acceleration of radioactive neutron rich species is now under development at LNL. Among the new instrumentation, the concept of gamma-ray tracking has been recently introduced in nuclear spectroscopy. A new gamma-ray detector array (AGATA) based on such technique is now under study in a wide european collaboration. The first sub-cluster of AGNFA is foreseen to be installed at the PRISMA spectrometer.