Collection efficiency of photoelectrons injected into dense ar gas at low and intermediate temperatures

We measured the collection efficiency of electrons injected by means of photoelectric effect into argon gas at high density at temperatures T=177.3 K, above the critical temperature, and T=142.6 K, below it, for several densities as a function of the applied electric field. We show that the experimental data can be interpreted in terms of the Young-Bradbury model if we take into account the multiple scattering effects that affect the electron-atom scattering cross section.