Ca 48 + Bk 249 fusion reaction leading to element Z=117: Long-lived α -decaying Db 270 and discovery of Lr 266

Abstract

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the Ca48+Bk249 fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope 117294 and its decay products. A hitherto unknown α-decay branch in Db270 (Z=105) was observed, which populated the new isotope Lr266 (Z=103). The identification of the long-lived (T1/2=1.0-0.4+1.9h) α-emitter Db270 marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an "island of stability." © 2014 American Physical Society.