Trapping Lifetime of Negative Ions in Rotating Superfluid Helium Under Pressure

Abstract

Measurements have been made of the lifetime for the escape of negative ions trapped in rotating helium II as a function of temperature and pressure. These measurements concern lifetimes in the range from 10 to 1000 sec, and have been made between the temperatures of 1.09 and 1.68°K from the vaporization pressure to the solidification pressure. At constant pressure the lifetime decreases rapidly with increasing temperature. The curves of constant lifetime in the pressure-versus-temperature plane have negative slopes $\frac{\mathrm{dP}}{\mathrm{dT}}$ and positive second derivatives $\frac{d^{2}P}{d{T}^2}$. The results have been interpreted in terms of the bubble model of the negative ion and the vortex-line model of the rotating superfluid. The interpretation suggests that the ion radius equals approximately 19.5 A at saturated vapor pressure and decreases to a value between 12 and 14 Å at the solidification pressure. However, a significant discrepancy between theory and experiment casts some doubt on the radius values obtained.