SPES (Selective Production of Exotic Species) is be a next generation ISOL-type accelerator facility aimed to develop a Radioactive Ion Beam (RIB) accelerator system dedicated to basic research in nuclear physics and nuclear astrophysics as well as to interdisciplinary applications, ranging from the production of radionuclide of medical interest to the generation of neutrons for material studies, nuclear technologies and medicine. SPES, together with the operation of existing machines, is the future of the Legnaro National Laboratory.

The unstable nuclei produced in a RIB facility are not commonly present on Earth, they are being produced in the advanced stages of stellar evolution. The most critical characteristic of these unstable nuclei is their ratio N/Z of neutrons to protons. In other words they can be more neutron rich or neutron deficient than the corresponding stable isotope.

If we figure all the nuclear species in a two-dimen¬sio¬nal graph in which one axis represents the number of neu¬¬trons and the other re¬pre¬sents the number of protons, each point plotted on the graph will represent a nucli¬de of a real or hypothetical che¬mi¬cal element. This sys¬tem of ordering nuclides is called the "Segrè diagram" in honour to Emilio Segrè and can offer a greater in¬sight into the charac¬te-ris¬tics of each of the isotopes of any element. All the sta¬ble isotopes we can find on earth fall in this plot, in the so called "valley of beta sta¬bi¬lity".

The most severe constraint on our ability to advance the understanding of nuclear physics over the past several decades has been the fact that in any nuclear reaction both the beam and target species were stable. This imposes limiting restrictions on the regions of the nuclear chart which can be accessed as well as on the type of information which can be obtained and most of our present knowledge of nuclear properties has been in fact gained by studying nuclei near the so called “valley of beta stability” or on the neutron- deficient side. Very asymmetric combinations of protons and neutrons are however expected to reveal new aspects of nuclear structure and the extremes in these quantities, which define the limits of nuclear existence, will be opened up for study with radioactive beam accelerators. (More…)