Drift Velocities of Slow Electrons in Helium, Neon, Argon, Hydrogen, and Nitrogen

TLDR

Drift velocities of electrons in He, Ne, Ar, H₂, and N₂ were measured over E/p = 10⁻⁴–10 V cm⁻¹ mm Hg and temperatures 77–373 K using an improved double‑shutter tube that eliminates end effects via small voltage pulses. Momentum‑transfer cross sections for 0.003–0.05 eV electrons were extracted, showing that He’s cross section is energy‑independent at 5.3×10⁻¹⁶ cm², while Ar, H, and N cross sections vary with energy and agree with the measured drift velocities.

Abstract

The drift velocities of electrons in helium, neon, argon, hydrogen, and nitrogen have been measured for $\frac{E}{p}$ values between ${10}^{\ensuremath{-}4}$ and 10 volt/cm-mm Hg at temperatures between 77\ifmmode^\circ\else\textdegree\fi{}K and 373\ifmmode^\circ\else\textdegree\fi{}K. The data were obtained from measurements of electron transit time in an improved version of the double-shutter tube developed by Bradbury and Nielsen. By applying sufficiently small voltage pulses to the control grids, it was possible to eliminate end effects present in previous experiments. Values of the momentum transfer cross sections for electrons with energies between about 0.003 and 0.05 ev are obtained which are consistent with the measured drift velocities for thermal electrons in helium, argon, hydrogen, and nitrogen. The derived momentum transfer cross section for electrons in helium is found to be independent of electron energy and equal to 5.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$. The momentum transfer cross sections for argon, hydrogen, and nitrogen vary with electron energy.