BUNCHING OF RADIOACTIVE ION-BEAM IN THE MILLISECOND REGION - A PULSEDGATING-POTENTIAL METHOD IN AN ION-SOURCE FOR ONLINE ISOTOPE-SEPARATION

A simple method of bunching radioactive ion beam in the millisecond re gion has been studied using an isotope separator on-line (ISOL). By ap plying positive and negative potential alternately between the exit ho le of a surface ionizer of the ISOL and an electrode set 1 mm apart fr om it, we have observed clear bunching effects for alkali elements hav ing relatively high ionization efficiencies. The bunching efficiency d efined as intensity ratio of the bunched beam to the usual DC beam was found to increase with the increase of repetition rate of the applied alternate potential; for example, at the duty factor of 20%, the bunc hing efficiencies for K-39, Na-23 and Li-7 ions were respectively 0.45 , 0.25 and 0.23 at 50 Hz, 0.78, 0.32 and 0.27 at 200 Hz and 1, 0.59 an d 0.42 at 1 kHz. The in-beam measurement using the Ca-40 (He-3, alphap )K-38 reaction showed nearly the same magnitude of the bunching effect s as in the case of K-39.