Geminate recombination of charges in irradiated liquid argon

Contrary to a recent suggestion [Phys. Rev. Lett. 40, 407 (1978)], the Onsager model of charge neutralization is not applicable to liquid argon irradiated by $\alpha$ particles. That model treats isolated ion-electron pairs. In $\alpha$-irradiated liquid argon the average distance between nearest-neighbor positive ions is about two orders of magnitude smaller than the Onsager length, so a columnar model (Jaffe or Kramers) must be used. The thermalization length of the hot electrons in liquid argon is about 200 nm.