Discovery of the New Element Z=117 and Confirmation of 115

Yu. Ts. Oganessian¹, J.H. Hamilton^2a and V.K. Utyonkov¹ for the collaboration

¹ Joint Institute for Nuclear Research, RU-141980, Dubna, Russian Federation
² Department of Physics and Astronomy, Vanderbilt University, USA and Collaboration with Oak Ridge National Laboratory, Lawrence Livermore National Laboratory and Research Institute of Atomic Reactors

^a email: j.h.hamilton@vanderbilt.edu

Published online: 19 October 2011

Abstract

The discovery of the new chemical element with atomic number Z=117 is presented. The isotopes ²⁹³ 117 and ²⁹⁴117 were produced in fusion reactions between ⁴⁸Ca and ²⁴⁹Bk. The ²⁴⁹Bk was produced in the High Flux Isotope Reactor and chemically separated at Oak Ridge. Decay chains involving eleven new nuclei were identified by means of the Dubna Gas-Filled Recoil Separator. The measured decay properties show a strong rise of stability for superheavy nuclei toward N=184.The reaction ²⁴³Am+⁴⁸Ca was studied at three energies. Twenty one decay chains of ²⁸⁸115 and one decay chain of ²⁸⁹115 were observed to confirm the earlier discoveries of Z=115 and 117.