Efficiency and delay of the fission ion guide for on-line mass separation

Abstract

Efficiency and time distribution of ions passing through an ion guide system, specially designed for on-line isotope separation of products of proton-induced fission, have been studied. This system, unlike the standard ion guide, consists of a separate, plasma-free thermalizing chamber for stopping the isotropically emitted fission fragments. This arrangement reduces the rate of the recombination losses of thermalized ions by the plasma electrons produced by the beam and results in very good and stable operating conditions. The total efficiency of the order of 10 −3 has been determined, nearly independent of the atomic number of the separated nuclide. The main reason for the limited efficiency is the inadequate stopping of the fragments in helium. The delay time distribution of the separated ions is measured to be broad, ranging from about 0.1 ms to 10 ms, the lower limit being set by the flight time through the separator. This has made possible the spectroscopy of short-lived beta-decaying nuclei and the discovery of new short-lived isomeric states, with ms half-lives, populated directly in fission.