The Momentum Transfer Cross Section for Electrons in Helium Derived from Drift Velocities at 77°K

Abstract

Drift velocities of electrons in helium at 76.8°K have been measured for 8 X lO⁻²⁰ ≤ E/N ≤ 2 X lO⁻¹⁷ V cm². From these data, and the earlier measurements of Crompton, Elford, and Jory made at 293°K, the energy-dependent momentum transfer cross section has been determined for electrons with energies between 0.008 and 6 eV. The present cross section agrees with that of Crompton, Elford, and Jory to within 1 %. The extension of the energy range to 8 meV permits a direct determination of the scattering length, for which a value of 1.19 a_o is obtained.