Theoretical analysis of free-ion yield in liquid Argon under low-let irradiation

The field enhancement of free-ion yield in liquid Argon and the concomitant reduction of radiation-induced luminescence implies an escape probability from recombination ∼ 0.35 at very low external fields. This, when interpreted using Onsager's equation, gives an electron thermalization length ∼ 200 nm which is larger than the inter-positive ion separation on the track (∼ 120 nm) obtained form the LET and W values. The thermalization length obtained by density scaling from the gas phase, is ∼ 103 nm, an even larger value. Because of the magnitudes of these distances the high energy electron track has approximate cylindrical symmetry and therefore the geminate recombination model is not appropriate for liquid argon and other liquefied rare gases. Another important factor is that the electron-cation recombination rate in liquid argon is only 1/20 of the diffusion controlled (Debye) value.