Luminescence of Helium II Produced by Weakα-Particle Sources

Measurements of the intensity of luminescence produced by weak $\alpha$-particle sources in He II are presented for $0.3<T<\mathrm{}4.2\mathrm{}$ °K, for different chamber sizes, and with an electric field applied in the region of the $\alpha$-particle source. With zero field the intensity exhibits a complex behavior, remaining approximately constant between $T_{\lambda }$ and 1.2 °K, then dropping to a minimum near 0.6 °K, and rising again at lower temperatures. The application of an electric field (up to 13 000 V/cm) in the source region reduces the intensity above 0.8 °K but increases it at lower temperatures. The transient behavior of the luminescence upon application of a pulsed field is described and discussed. The qualitative features of the temperature dependence of the luminescence are accounted for in terms of radiation from metastable systems, the diffusion coefficient of which rises exponentially ($\sim e^{\frac{\Delta }{\mathrm{kT}}}$) as the temperature drops. Approximate values of the diffusion coefficient are presented. The electric-field-induced amplification of the luminescence below 0.8 °K is attributed to metastable interactions with charged vorticity.