Impurities in superfluid helium detected via radioactivity

High-speed radioactive nuclei B-12 (T-1/2 = 20.3 ms), Li-8 (T-1/2 = 838ms), and N-17 (T-1/2 = 4.17s) were introduced into liquid helium at temperatures 4.20-1.15 K. The impurities were individually detected with a multi-counter detection system, which resolved the position and time of the beta-ray emission. Two regimes for the impinged impurities were observed; snowballs and neutrals. The snowballs involving a radioactive core ion (B-12, Li-8, or N-17) were transported under a static electric field and stored. In this experiment, the snowballs were successfully separated from the neutrals and the motion of the snowballs was clearly recorded by the detection system. (C) 2000 Elsevier Science B.V. All rights reserved.