Synthesis of superheavy nuclei in ⁴⁸Ca induced reactions

The paper presents on the synthesis of superheavy nuclides with Z=114 and 116 produced in the fusion reactions with ⁴⁸Ca ions, performed within the JINR-LLNL collaboration in 2000-2001 using the heavy ion accelerator U-400 of the Flerov Laboratory of Nuclear Reactions (Dubna). In the irradiation of targets made from enriched ²⁴⁴Pu and ²⁴⁸Cm isotopes with beam doses of 1.5·10¹⁹ and 2.3 ·10¹⁹, respectively, the detector array situated in the focal plane of the gas-filled separator registered heavy atoms of new elements undergoing sequential α-decays terminated by spontaneous fission. The time range of the decay chains is approximately one min. Decay properties of the synthesized nuclei are consistent the consecutive α-decays originating from the parent nuclides ²⁸⁸114 ²⁹⁶116 produced in the 4n-evaporation channels with the cross section of about a picobarn. Comparison of T_SF and T_α values for the nuclei with Z=110 and 112 with those obtained earlier for more light isotopes of these elements points to an enhanced stability of heavy nuclei with an increase in the neutron number. The α-decay energies Q_α measured experimentally in the chains 116 - α₁ - 114 - α₂ - 112 - α₃ - 110 are compared with theoretical predictions of different nuclear models. This comparison shows that theoretical predictions concerning the existence of the islands of stability in the region of superheavy elements has been experimentally confirmed not only qualitatively but also to some extent quantitatively. The prospects of further investigations in the field of superheavy nuclei are discussed briefly. (author)