Ionization of Short-Lived Nuclides in the Hot Disc-Shaped Cavity

Abstract

The numerical model of ionization in disc-shaped cavities that takes into account both the radioactive decay of the nuclide and the delay of the emission due to the particle–wall sticking is presented. The dependences of ionization efficiency on timescales characterizing radioactive decay and sticking are presented and discussed. Two different cavity shapes are considered. One of them is a flat disc cavity, more suitable for stable or long-lived but hard-to-ionize isotopes. The other is a compact cavity, superior for short-lived nuclides, especially those easy-to-ionize. Average times the particle stays inside the cavity have been estimated — these times are more than an order of magnitude shorter in the case of a compact cavity. The influence of the extraction opening size on the efficiency of ionization in the flat disc cavity is discussed. It is shown that increasing this opening is an easy way to increase efficiency in the case of short-lived isotopes. The current–voltage curves calculated for both cavity configurations are presented. It is proved that the optimal extraction voltages for the compact and flat disc configurations are 0.5 kV and 2 kV, respectively.