Mobilities of Uranium and Mercury Ions in Helium

The mobilities of mass‐identified U⁺ and Hg⁺ ions in helium have been determined in a drift tube‐mass spectrometer apparatus. For uranium ions a reduced mobility value ${\mu }_0\text{=(16.0± 0.5)}{\mathrm{cm}}^2/\mathrm{V}·\sec$ is obtained at 305°K and a standard gas density of ${\text{2.69× 10}}^{19}{\mathrm{cm}}^{\text{−3}}.$ The mobility of mercury ions is ${\mu }_0\text{=(19.4± 0.5)}{\mathrm{cm}}^2/\mathrm{V}·\sec$ at 292°K, in agreement with two previous determinations. The effect of fast ion injection in drift mobility measurements is discussed, and a new technique to circumvent these problems is described. The results are compared with existing theories of ion mobilities.