Study Of Neutron-Deficient Isotopes Of Fl In The Pu-239, Pu-240+Ca-48 Reactions

The results of the experiments aimed at the synthesis of Fl isotopes in the Pu-239 + Ca-48 and Pu-240 + Ca-48 reactions are presented. The experiment was performed using the Dubna gas-filled recoil separator at the U400 cyclotron. In the Pu-239+Ca-48 experiment one decay of spontaneously fissioning (284)Fl was detected at 245-MeV beam energy. In the Pu-240+Ca-48 experiment three decay chains of (285)Fl were detected at 245 MeV and four decays were assigned to (284)Fl at the higher Ca-48 beam energy of 250 MeV. The. alpha-decay energy of (285)Fl was measured for the first time and decay properties of its descendants (281)Cn, (277)Ds, (273)Hs, (269)Sg, and (265)Rf were determined more precisely. The cross section of the Pu-239( Ca-48,3n) (284)Fl reaction was observed to be about 20 times lower than those predicted by theoretical models and 50 times less than the value measured in the Pu-244+Ca-48 reaction. The cross sections of the Pu-240( Ca-48,4-3n) 284,(285)Fl at both Ca-48 energies are similar and exceed that observed in the reaction with lighter isotope Pu-239 by a factor of 10. The decay properties of the synthesized nuclei and their production cross sections indicate rapid decrease of stability of superheavy nuclei with departing from the neutron number N= 184 predicted to be the next magic number.