Temperature Dependent Mobility Measurements of Alkali-Earth Ions in Superfluid Helium (4He)

Mobility measurements of alkali-earth ions Be + , Mg + , Ca + , Sr + and Ba + in the temperature range 1.27 to 1.66 K are presented. The mobility of Be + shows a different behavior in comparison to that of Mg + , although the properties of the two elements are similar. This may suggest that Be + forms an alternate structure, perhaps a snowball, compared to the bubble like defect of Mg + .