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

TL;DR

This study investigates how an electric field influences the intensity and timing of scintillation in superfluid helium caused by alpha particles, revealing partial ionization and recombination mechanisms affecting the light emission.

Contribution

It provides new quantitative analysis of electric field effects on helium scintillation and elucidates the roles of excited states and ionization in the process.

Findings

Prompt scintillation reduces by 15% at 45 kV/cm

Approximately 40% of scintillation from excited atoms

60% from ionization and recombination

Abstract

We report a study of the intensity and time dependence of scintillation produced by weak alpha particle sources in superfluid helium in the presence of an electric field (0 - 45 kV/cm) in the temperature range of 0.2 K 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, this electric field dependence leads to the conclusion that roughly 40% of the scintillation results 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.