Experiments are described and first results are presented on the synthesis
of superheavy nuclei in Ca-48-induced reactions. The experiments were carri
ed out at the FLNR Dubna heavy ion cyclotron U400 using the electrostatic s
eparator VASSILISSA and the Dubna Gas-Filled Recoil Separator (DGFRS) in th
e framework of a large collaboration with GSI (Darmstadt), LLNL (Livermore)
, RIKEN (Wako-shi, Saitama) and the Comenius University (Bratislava).
In the period from March 1998 till August 2000 five experiments were carrie
d out: U-238(Ca-48, 3n)(283)112, Pu-244(Ca-48, 3n)(289)114, Pu-242(Ca-48, 3
n)(287)114, Pu-244(Ca-48, 4n)(288)114 and Cm-248(Ca-48, 4n)(292)116. The to
tal beam dose amounted to approximate to 4.5 . 10(19) (3.5 mg Ca-48).
The observed significant increase in the half-lives of the superheavy isoto
pes, situated in the vicinity of the predicted closed shells 2=114, N=184,
confirm the conclusion of theoretical models about the decisive influence o
f the nuclear structure on the stability of superheavy elements.