The synthesis of superheavy nuclei in the 48 Ca + 244 Pu reaction

The first results of experiments on the synthesis of superheavy nuclei, for which the modern nuclear theory predicts significant increase in stability, are presented. In a 34-day bombardment of a 244 Pu target with 5.2 x 101848 Ca ions using the Dubna Gas-filled Recoil Separator we observed a decay sequence consisting of an implanted heavy atom, three subsequent α-decays and spontaneous fission of heavy nuclei. The measured α-energies and corresponding time intervals were: Eα 9.71 MeV (Δt = 30.4 s), 8.67 MeV (Δt = 15.4 min) and 8.83 MeV (Δt = 1.6 min); for the spontaneous fission (Δt = 16.5 min), the total deposited energy was approximately 190 MeV. The large alpha-particle energies together with the long decay times and spontaneous fission terminating the chain offer evidence of the decay of nuclei with high atomic numbers. The best candidate for the observed decay sequence is α-decay of the parent nucleus 289 114 produced in the 244 Pu (48 Ca, 3n) reaction with a section of about 1 pb. The lifetimes and α-particle energies of all observed new nuclei are in agreement with theoretical predictions for odd-even isotopes 289 114, 285 112 and 281 110. The significant increase in the lifetimes of the new Z = 112 and 110 daughters of the Z=114 nuclide (by a factor of ∼ 106) with respect to the known heaviest isotopes of elements 112 and 110 can be considered direct proof of the existence of the 'island of stability' of superheavy elements. (Author) 22 refs., 7 figs