Ca-48+Bk-249 Fusion Reaction Leading to Element Z=117: Long-Lived alpha-Decaying (270)Db and Discovery of Lr-266

Abstract

[Introduction] The superheavy element with atomic number Z ¼ 117 was produced as an evaporation residue in the 48 Ca þ 249 Bk 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- μ s and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope 294 117 and its decay products. A hitherto unknown α -decay branch in 270 Db ( Z ¼ 105 ) was observed, which populated the new isotope 266 Lr ( Z ¼ 103 ). The identification of the long-lived ( T 1 = 2 ¼ 1 . 0 þ 1 . 9 − 0 . 4 h) α -emitter 270 Db marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an “ island of stability. ”