The exact location of the stability regions of superheavy nuclei is not known, it varies and depends upon the nuclear structure models and on the interactions used to perform the calculations.
The area around the element with Z=114 protons and N=184 neutrons has been predicted theoretically as a possible stability region. This has triggered the investigation for the formation of compound nuclei of charge Z~114.
The LENA group has led several studies of superheavy nuclei, following mainly two approaches with indirect methods : the measurements of fission times of very heavy nuclei (Z>120) and the spectroscopy of Transfermium nuclei (Z>100). It is possible via these methods to study the possible island of stability (between 114 and 126 protons, and towards 184 neutrons) and its extension, without having to synthesize these nuclei, for which the production cross sections are very low (experiments for the production would require months of measurements).
See the page of the experiments on superheavy nuclei, performed between 2000 and 2008 with the FULIS device, rotating target developed for the studies of the superheavy formation.
The group participated to the experimental campaigns at GANIL, using the method of the time fission measurements. Several experiments showed the relative stability of nuclei around 120-124 protons. The FINOL (FIssion des NOyaux Lourds, Fission of Superheavy nuclei) experiment showed, for the first time, the formation of a compound nucleus Z=120.
Several experiments were carried out in Jyväskylä (Finland) and at GANIL to perform the spectroscopy of one particle states of odd isotope of 255No (Z=102) and of mendelevium, 251Md et 249Md (Z=101). For the first time, a spectroscopic measurement of gamma and correlated electrons was carried out in 2012 with the SAGE detector, revealing new states. Interesting results have been obtained by the study of quasi-particle states in 252No, 250Fm, and 256Rf, which appear as K isomers. These experiments provide information on the structure of these very heavy nuclei, but the configurations of the states involve nuclear orbitals which also play a role in the stability of superheavy nuclei around the stability island.
Contacts: (fission times) A. Drouart, (transfermium) Ch. Theisen