Production of zero energy radioactive beams through extraction across superfluid helium surface

A radioactive ²²³Ra source was immersed in superfluid helium at 1.2-1.7 K. Electric fields transported recoiled ²¹⁹Rn ions in the form of snowballs to the surface and further extracted them across the surface. The ions were focussed onto an aluminium foil and alpha particle spectra were taken with a surface barrier spectrometer. This enabled us to determine the efficiency for each process unambiguously. The pulsed second sound wave proved effective in enhancing the extraction of positive ions from the surface. Thus we offer a novel method for study of impurities in superfluid helium and propose this method for production of zero energy nuclear beams for use at radioactive ion beam facilities.