Hot electrons have been injected into very dense argon, nitrogen, and hydrogen gases and liquids. The current-voltage characteristics are experimentally determined for densities (N) of argon, nitrogen. and hydrogen ranging from about J(fo to 10 22 cm-3 and applied fields (E) ranging from about 10 to 10" V em-I. The argon data show a square root E IN dependence of the current. The nitrogen and hydrogen data show a complicated dependence of the current on E IN due to the rapid thermalization in the region of the image potential of the injected electrons through inelastic collision processes not present in argon. A hydrodynamic-two-fluid model is developed to analyze the nitrogen and hydrogen data. From the analysis of our data, we obtain the density dependence of the momentum exchange scattering cross section and the energy relaxation time for the injected hot electrons.

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Press, Oxford, England, 1955). 10 We are employing the results of Ref. 2 in our discussion of thermal conductivity. Various aspects of this problem have been treated by others. For example: the phenomena of Poiseuille flow in a phonon gas were first suggested by J. A. Sussman and A. Thellung, Proc.The transport coefficients of a normal Fermi liquid in the extreme low-temperature limit and the leading finite-temperature contributions to the transport coefficients are studied using the quasiparticle transport equation. The scattering amplitude for quasiparticles on the Fermi surface is expressed in terms of Landau parameters, using an approximation which takes into account s-and £-wave scattering; the calculated values of the transport coefficients in the extreme low-temperature limit for liquid He are shown to be in good agreement with the experimental values. Finite-temperature contributions to the transport coefficients are expressed in terms of the solution of the transport equation in the extreme low-temperature limit, and explicit calculations are performed for the case of liquid He . Assuming Landau parameters with I > 2 vanish, an estimate of the Landau parameter F t a for liquid He is obtained by comparing the theoretical and experimental values of the leading finite-temperature contributions to the transport coefficients.

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