Bunching of radioactive ion beam in the millisecond region - a pulsed gating-potential method in an ion source for on-line isotope separation

A simple method of bunching radioactive ion beam in the millisecond region has been studied using an isotope separator on-line (ISOL). By applying positive and negative potential alternately between the exit hole of a surface ionizer of the ISOL and an electrode set 1 mm apart from it, we have observed clear bunching effects for alkali elements having relatively high ionization efficiencies. The bunching efficiency defined 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 bunching efficiencies for ³⁹K, ²³Na and ⁷Li 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 and 0.42 at 1 kHz. The in-beam measurement using the ⁴⁰Ca (³He, αp)³⁸K reaction showed nearly the same magnitude of the bunching effects as in the case of ³⁹K.