Observation of Superheavy Nuclei Produced in the Reaction of K 86 r with P 208 b

Following a prediction by Smolańczuk [Phys. Rev. C 59, 2634 (1999)], we searched for superheavy element formation in the bombardment of 208Pb with 449-MeV 86Kr ions. We have observed three decay chains, each consisting of an implanted heavy atom and six subsequent α decays, correlated in time and position. In these decay chains, a rapid (ms) sequence of high energy α particles ( Eα≥10MeV) indicates the decay of a new high- Z element. The observed chains are consistent with the formation of 129318 and its decay by sequential α-particle emission to 128916, 128514, 128112, 127710, 273Hs ( Z=108) and 269Sg ( Z=106). The production cross section is 2.2−0.8+2.6pb.