Experiments on the synthesis of element 115 in the reactionAm243(Ca48,xn)115291−x

The results of experiments designed to synthesize element 115 isotopes in the ${}^{243}\mathrm{Am}+{}^{48}\mathrm{Ca}$ reaction are presented. With a beam dose of $4.3\times {10}^{18}$ $248\text{−}\text{MeV}$ ${}^{48}\mathrm{Ca}$ projectiles, we observed three similar decay chains consisting of five consecutive $\alpha$ decays, all detected in time intervals of about $20\mathrm{s}$ and terminated at a later time by a spontaneous fission with a high-energy release (total kinetic energy $\sim 220\text{MeV}$). At a higher bombarding energy of $253\text{MeV}$, with an equal ${}^{48}\mathrm{Ca}$ beam dose, we registered a different decay chain of four consecutive $\alpha$ decays detected in a time interval of about $0.5\mathrm{s}$, also terminated by spontaneous fission. The $\alpha$ decay energies and half-lives for nine new $\alpha$-decaying nuclei are given. The decay properties of these synthesized nuclei are consistent with consecutive $\alpha$ decays originating from the parent isotopes of the new element 115, ${}^{288}115$ and ${}^{287}115$, produced in the $3n$- and $4n$-evaporation channels with cross sections of about $3\text{pb}$ and $1\text{pb}$, 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.