Study of the average charge states of 188 Pb and 252,254 No ions at the gas-filled separator TASCA

The average charge states of 188Pb and 252,254No ions in dilute helium gas were measured at the gas-filled recoil separator TASCA. Hydrogen gas was also used as a filling gas for measurements of the average charge state of 254No. Helium and hydrogen gases at pressures from 0.2mbar to 2.0mbar were used. A strong dependence of the average charge state on the pressure of the filling gases was observed for both, helium and hydrogen. The influence of this dependence, classically attributed to the so-called “density effect”, on the performance of TASCA was investigated. The average charge states of 254No ions were also measured in mixtures of helium and hydrogen gases at low gas pressures around 1.0mbar. From the experimental results simple expressions for the prediction of average charge states of heavy ions moving in rarefied helium gas, hydrogen gas, and in their mixture were derived.