Superheavy Elements at Berkeley: The Culmination of Seaborg’s Career

Abstract

Through many years and many heavy element research projects, Seaborg always brought the authors’ thoughts and discussions back to the superheavy elements (SHE). This guidance led to the construction of the Berkeley Gasfilled Separator (BGS) with its primary program being a search for superheavy elements. In April and May of 1999, the BGS was used to search for the production and decay of element 118 from the 86Kr+ 208Pb reaction according to Smolanczuk’s predictions of relatively large production rates. Three decay chains, each consisting of an implanted heavy ion, followed by a rapid (ms) succession of high-energy (> 10 MeV) alpha-particle decays were detected. These chains are consistent with the production and decay of element 118 with mass number 293. These results a) show experimental evidence for the existence of shell-stabilized SHE, b) provide experimental values for refinement of nuclear mass models in the SHE region, and, most importantly, c) present a “new” reaction pathway for the production of SHE.