Study of Radioactive Snowballs in Superfluid Helium

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Impurity ions introduced in liquid helium may behave as singly charged entities with effective mass of 50-100 He atoms, which are referred to as snowballs. A snowball is. therefore, an aggregate, a micro-cluster of helium atoms by means of electrostriction around an impurity core ion admitted in liquid helium. not only helium ions as first noticed but also other alien ions do form snowballs. The method used in the of study of polarization phenomena in heavy ion reactions enabled us to conceive renewed interests to approach individual snowballs though alpha- and beta-ray countings, which have been developed here.While the snowball has been thought of a highly paramount solid entity, there are still doubt whether all the existing evidences do decisively favor the picture of a solid core. The preservation of nuclear polarization in this research provided with an important clue to this issue, enabling us to test the inherent structure of snowballs directly as to peripheral problems of the above experiment.The radioactive nuclear beams from the SIS accelerator at GSI Darmstadt was examined and finally focussed for of snowball experiments. The intensity and focussing were enough for that purpose.The lifetime obtained for snowballs indicates the interaction responsible is not that with simple electrons but with basic excitations in liquid helium.The structure of snowball became clearly highly symmetric, as it was compared with the crystal structure composed of metal ion and hydrogen ions. This is an interesting point of view for understanding of maintaining nuclear polarization in the core ion trapped in a snowball.