D. Ward

The superheavy element with atomic number Z 117 was produced as an evaporation residue in the 48 Ca 249 Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their -decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-s and a few days. Two decay chains comprising seven decays and a spontaneous fission each were identified and are assigned to the isotope 294 117 and its decay products. A hitherto unknown -decay branch in 270 Db (Z 105) was observed, which populated the new isotope 266 Lr (Z 103). The identification of the long-lived (T 1=2 1.0 1.9 -0.4 h) -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."

A high-resolution α, x-ray, and γ-ray coincidence spectroscopy experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung. Thirty correlated α-decay chains were detected following the fusion-evaporation reaction 48Ca + 243Am. The observations are consistent with previous assignments of similar decay chains to originate from element Z=115. For the first time, precise spectroscopy allows the derivation of excitation schemes of isotopes along the decay chains starting with elements Z>112. Comprehensive Monte Carlo simulations accompany the data analysis. Nuclear structure models provide a first level interpretation.

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the (48)Ca+(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-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 (294)117 and its decay products. A hitherto unknown α-decay branch in (270)Db (Z = 105) was observed, which populated the new isotope (266)Lr (Z = 103). The identification of the long-lived (T(1/2) = 1.0(-0.4)(+1.9) 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."