An EC-branch in the decay of 27-s 263Db: Evidence for the isotope 263Rf

27-s 2 6 3 Db was produced in the 2 4 9 Bk ( 1 8 O, 4n) reaction at 93 MeV. The activity was transported by a He/ KCl-jet to the laboratory where it was collected for 15 min and then subjected to a chemical separation specific for group-4 elements. The activity was dissolved in 0.5 M unbuffered α-HiB and eluted from a cation-exchange column. The effluent was made 9 M in HCl and group-4 tetrachlorides were extracted into TBP/Cyclohexane which was evaporated to dryness on a Ta disc. The Ta discs were assayed for a and SF activity. A SF activity with a half life on the order of 20 min was observed and assigned to the nuclide 2 6 3 Rf. It is formed by electron-capture decay of 2 6 3 Db with a decay branch of 3 + 4 %.