Transport of recoil atoms in a stream of liquid-air-cooled pure helium

Abstract Pure commercial helium cooled down to the temperature of liquid air (80 K) has been used for rapid transportation of recoil atoms over distances as long as 10 m. Transport efficiencies of several tens of per cent have been obtained for recoil atoms resulting from alpha decay or from decay by fission. The angle of divergence of the beam of recoil atoms at the exit of the transport capillary is measured to be (11±2)° for particles of mass number A = 211. Experimental results are discussed in terms of thermal diffusion. The elimination of carrier vapors will probably simplify the use of the helium-jet technique in on-line mass separators.