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 μ₀=(16.0± 0.5) cm²/V.sec is obtained at 305°K and a standard gas density of 2.69× 10¹⁹cm^-3. The mobility of mercury ions is μ₀=(19.4± 0.5) cm²/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.