How elements up to 118 were reached and how to go beyond

¹ Institute of Nuclear Chemistry, Johannes Gutenberg University, 55128 Mainz, Germany
² GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany
³ Helmholtz Institute Mainz, 55099 Mainz, Germany
⁴ Australian National University, Canberra, ACT 2601, Australia

^* e-mail: duellmann@uni-mainz.de

Published online: 22 November 2017

Abstract

The new superheavy elements with Z=113, 115, 117, and 118 were recently accepted into the periodic table and have been named. Elements with Z≥112 are predominantly produced in ⁴⁸Ca-induced fusion reactions on actinide targets. This pathway is exhausted at Z=118 due to the lack of target materials with sufficiently high proton number to reach elements with Z≥119. Search experiments for yet heavier elements were performed at GSI Darmstadt and FLNR Dubna. The reactions ⁵⁰Ti + ²⁴⁹Bk, which leads to Z=119, as well as ⁶⁴Ni + ²³⁸U, ⁵⁸Fe + ²⁴⁴Pu, ⁵⁴Cr + ²⁴⁸Cm, and ⁵⁰Ti + ²⁴⁹Cf, leading to Z=120, have been studied. Despite a total duration of these experiments of more than one year, neither succeeded in the identification of a new element. To obtain improved guidance for better-informed search experiments, nuclear reaction studies appear necessary and have recently started. Also technical advances will be an important pillar to this end. At GSI, work towards a new continuous-wave linear accelerator is ongoing and is briefly described.