Effect of an electric field on superfluid helium scintillation produced by $\alpha$-particle sources

Abstract

We report a study of the intensity and time dependence of scintillation produced by weak $\alpha$ -particle sources in super fluid helium in the presence of an electric field (0-45 kV/cm) in the temperature range of 0.2 to 1.1 K at the saturated vapor pressure. Both the prompt and the delayed components of the scintillation exhibit a reduction in intensity with the application of an electric field. The reduction in the intensity of the prompt component is well approximated by a linear dependence on the electric-field strength with a reduction of 15% at 45 kV/cm. When analyzed using the Kramers theory of columnar recombination, thiselectricfielddependence leads to the conclusion that roughly 40% of thescintillationresults from species formed from atoms originally promoted to excited states and 60% from excimers created by ionization and subsequent recombination with the charges initially having a cylindrical Gaussian distribution about the $\alpha$ track of 60 nm radius. The intensity of the delayed component of the scintillation has a stronger dependence on the electric field strength and on temperature. The implications of these data on the mechanisms affecting scintillation in liquid helium are discussed.