Study of neutron-deficient isotopes of Fl in the 239Pu, 240Pu + 48Ca reactions

[摘要] The results of the experiments aimed at the synthesis of Fl isotopes in the239Pu +48Ca and240Pu +48Ca reactions are presented. The experiment was performed using the Dubna gas-filled recoil separator at the U400 cyclotron. In the239Pu+48Ca experiment one decay of spontaneously fissioning284Fl was detected at 245-MeV beam energy. In the240Pu+48Ca experiment three decay chains of285Fl were detected at 245 MeV and four decays were assigned to284Fl at the higher48Ca beam energy of 250 MeV. The α-decay energy of285Fl was measured for the first time and decay properties of its descendants281Cn,277Ds,273Hs,269Sg, and265Rf were determined more precisely. The cross section of the239Pu(48Ca,3n)284Fl 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 244Pu+48Ca reaction. The cross sections of the240Pu(48Ca,4-3n)284,285Fl at both48Ca energies are similar and exceed that observed in the reaction with lighter isotope239Pu 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.

[发布机构] Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna; RU-141980, Russia^1;Department of Physics and Astronomy, Oak Ridge National Laboratory, Oak Ridge; TN; 37831, United States^2;Department of Physics and Astronomy, University of Tennessee, Knoxville; TN; 37996, United States^3;Faculty of Physics, University of Warsaw, Warsaw, Poland^4;Science and Technology Partnerships Direc., Oak Ridge National Laboratory, Oak Ridge; TN; 37831, United States^5;Department of Physics and Astronomy, Vanderbilt University, Nashville; TN; 37235, United States^6;Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore; CA; 94551, United States^7;Department of Physics, University of Notre Dame, Notre Dame; IN; 46566, United States^8

[关键词] Beam energies;Decay chains;Decay properties;Gas-filled recoil separator;Magic numbers;Neutron number;Production cross section;Stability of superheavy nucleus