Europhys. Lett.
Volume 63, Number 5, September 2003
Page(s) 687 - 693
Section Nuclear Physics
Published online 01 November 2003
DOI: 10.1209/epl/i2003-00576-1
Europhys. Lett., 63 (5) , pp. 687-693 (2003)

Extraction of radioactive positive ions across the surface of superfluid helium: A new method to produce cold radioactive nuclear beams

W. X. Huang1, 2, P. Dendooven3, K. Gloos4, N. Takahashi5, J. P. Pekola1 and J. Äystö1

1  Department of Physics, PB 35 (YFL), University of Jyväskylä - FIN-40014, Finland
2  Institute of Modern Physics, Chinese Academy of Sciences - Lanzhou 730000, PRC
3  KVI - Zernikelaan 25, 9747 AA Groningen, The Netherlands
4  Ørsted Laboratory, Niels Bohr Institute - Universitetsparken 5 DK-2100 Copenhagen, Denmark
5  Osaka Gakuin University - Suita/Osaka, 564-8511, Japan

(Received 23 April 2003; accepted 20 June 2003)

Alpha-decay recoils $\chem{{}^{219}Rn}$ were stopped in superfluid helium and positive ions were extracted by electric field into the vapour phase. This first quantitative observation of extraction was successfully conducted using highly sensitive radioactivity detection. The efficiency for extraction across the liquid surface was $23\pm 4\%$ at 1.60 $\un{K}$, the release time was $90\pm 10$ $\un{ms}$ at 1.50 $\un{K}$ and the barrier for positive ions through a free superfluid-helium surface was $19.4\pm 4.5$ $\un{K}$. The pulsed second sound proved to be effective in enhancing the extraction.

29.90.+r - Other topics in elementary-particle and nuclear physics experimental methods and instrumentation.
67.40.Jg - Ions in liquid $\chem{{}^4He}$.
29.27.Ac - Beam injection and extraction.

© EDP Sciences 2003