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Physical Review Letters

Pressure Dependence of the Radius of the Negative Ion in Helium II

B. E. Springett, R. J. Donnelly

Published Aug 15, 1966• 68 citations
Publisher

Abstract

The pressure dependence of the radius of the negative ion in helium II is derived from measurements of trapping cross section in quantized vortex lines.Received 20 June 1966DOI:https://doi.org/10.1103/PhysRevLett.17.364©1966 American Physical Society

DOI
10.1103/physrevlett.17.364

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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\ifmmode^\circ\else\textdegree\fi{}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 \AA{} at the solidification pressure. However, a significant discrepancy between theory and experiment casts some doubt on the radius values obtained.

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We have studied negative-ion absorption by rotating He II from 0.98\ifmmode^\circ\else\textdegree\fi{}K to 1.7\ifmmode^\circ\else\textdegree\fi{}K. Measurements of vortex-line capture cross sections are reported as a function of temperature (0.98\ifmmode^\circ\else\textdegree\fi{}K to 1.7\ifmmode^\circ\else\textdegree\fi{}K at three electric fields (16.3, 49.0, and 97.9 V/cm) and as a function of electric field (10 to 200 V/cm) at two temperatures. Great care was taken to insure that the reported cross-section values were not affected by space-charge effects. The results are found in good agreement with the ion-capture theories developed by Donnelly and Roberts. The decrease in cross section above 1.6\ifmmode^\circ\else\textdegree\fi{}K is in agreement with the escape calculation of Parks and Donnely and supports their value of 15.96 \AA{} for the negative-ion radius.

Physical Review•Dec 2, 1966•58 citations

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J. Cooper

Received 23 September 1966DOI:https://doi.org/10.1103/PhysRevLett.17.991©1966 American Physical Society

Physical Review Letters•Nov 7, 1966•12 citations
The pressure dependence of the radius of the negative ion in helium II is derived from measurements of trapping cross section in quantized vortex lines.Received 20 June 1966DOI:https://doi.org/10.1103/PhysRevLett.17.364©1966 American Physical Society
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\ifmmode^\circ\else\textdegree\fi{}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 dPdT\frac{\mathrm{dP}}{\mathrm{dT}}dTdP​ and positive second derivatives d2PdT2\frac{{d}^{2}P}{d{T}^{2}}dT2d2P​. 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 \AA{} at the solidification pressure. However, a significant discrepancy between theory and experiment casts some doubt on the radius values obtained.
We have studied negative-ion absorption by rotating He II from 0.98\ifmmode^\circ\else\textdegree\fi{}K to 1.7\ifmmode^\circ\else\textdegree\fi{}K. Measurements of vortex-line capture cross sections are reported as a function of temperature (0.98\ifmmode^\circ\else\textdegree\fi{}K to 1.7\ifmmode^\circ\else\textdegree\fi{}K at three electric fields (16.3, 49.0, and 97.9 V/cm) and as a function of electric field (10 to 200 V/cm) at two temperatures. Great care was taken to insure that the reported cross-section values were not affected by space-charge effects. The results are found in good agreement with the ion-capture theories developed by Donnelly and Roberts. The decrease in cross section above 1.6\ifmmode^\circ\else\textdegree\fi{}K is in agreement with the escape calculation of Parks and Donnely and supports their value of 15.96 \AA{} for the negative-ion radius.