The heaviest elements provide a unique laboratory to study nuclear structure and nuclear dynamics under the influence of large Coulomb forces and large mass (A). Super Heavy Elements (SHE) are nuclei with vanishing liquid-drop fission barrier and are therefore entirely stabilized by quantum shell effects. Due to the large density of single-particle levels and strongly polarizing Coulomb field, theoretical predictions of magic numbers are extremely model dependent. Furthermore, shell closures for one nucleon species depend strongly on the number of the other species. The extra binding from shell effects is not localised like in lighter mass regions but rather spread over all the shell closures. Finally, semi-bubble proton and neutron density profiles lead to anomalies of the spin-orbit splitting, which may disappear or even be reversed for certain orbitals. For all these reasons, only a systematic study of the structure of heavy nuclei can help in the development of better interactions and provide discriminating tests of models.
In 2003, an IN2P3-JINR (CSNSM-IReS-FLNR) collaboration launched a project of electron and gamma-ray spectroscopic studies of heavy nuclei at the FLNR in Dubna. This project will benefit from the radioactive actinide targets uniquely available at Dubna and from the very intense stable beams provided by the U400 cyclotron.
The GABRIELA (Gamma Alpha Beta Recoil Investigations with the ELectromagnetic Analyser) set-up has been designed to detect the arrival of reaction products and their subsequent radioactive decays involving the emission of α- and β-particles, fission fragments, γ- and X-rays and conversion electrons. It was installed at the focal plane of the recoil separator VASSILISSA and is now at the focal plane of SHELS.