Gamma and electron spectroscopy of transfermium isotopes at Dubna: Results and plans

International audienceDetailed spectroscopic information of excited nuclear states in deformed transfermium nuclei is scarce. Most of the information available today has been obtained from investigations of fine-structurer alpha-decay. Although alpha decay gives access to hindrance factors and lifetimes which are strongly correlated to shell/subshell closures and the presence of isomers, only the combined use of gamma and conversion electron spectroscopy allows the precise determination of excitation energy, spin and parity of nuclear levels. In the years 2004-2009 using the GABRIELA set-up [Hauschild et al, Nucl. Instrum. Methods A560, 388 (2006)] at the focal plane of VASSILISSA separator [Malyshevet al, Nucl. Instrum. Methods A440, 86(2000); A516, 529(2004)] experiments with the aim of gamma and electron spectroscopy of the isotopes from Fm to Lr, formed by complete fusion reactions with accelerated heavy ions were performed. In the following, the preliminary results of decay studies using alpha-gamma and alpha-beta coincidences at the focal plane of the VASSILISSA recoil separator are presented. Accumulated experience allowed us to perform ion optical calculations and to design the new experimental set-up, which will collect the base and best parameters of the existing separators and complex detector systems used at the focal planes of these installations. In the near future it is planned to study neutron-rich isotopes of the Rf-Sg in the 'hot' fusion reactions with (22)Ne incident projectiles and (242)Pu, (243)Am and (248)Cm target