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+.