Experiments on the synthesis of element 115 in the reaction ²⁴³Am(⁴⁸Ca,xn)^291−x115

The results of experiments designed to synthesize element 115 isotopes in the ²⁴³Am+⁴⁸Ca reaction are presented. With a beam dose of 4.3×10¹⁸ 248-MeV ⁴⁸Ca projectiles, we observed three similar decay chains consisting of five consecutive α decays, all detected in time intervals of about 20 s and terminated at a later time by a spontaneous fission with a high-energy release (total kinetic energy ∼220 MeV). At a higher bombarding energy of 253 MeV, with an equal ⁴⁸Ca beam dose, we registered a different decay chain of four consecutive α decays detected in a time interval of about 0.5 s, also terminated by spontaneous fission. The α decay energies and half-lives for nine new α-decaying nuclei are given. The decay properties of these synthesized nuclei are consistent with consecutive α decays originating from the parent isotopes of the new element 115, ²⁸⁸115 and ²⁸⁷115, produced in the 3n- and 4n-evaporation channels with cross sections of about 3 pb and 1 pb, respectively. The radioactive properties of the new odd-Z nuclei (105–115) are compared with the predictions of the macroscopic-microscopic theory. The experiments were carried out at the U400 cyclotron with the recoil separator DGFRS at FLNR, JINR.