Free-ion yield in liquid argon induced byAm241-αirradiation

Recent measurement of free-ion yield in liquid argon by Gruhn and Edmiston [Phys. Rev. Lett. 40, 407 (1978)] using ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$-$\alpha$ irradiation has been analyzed using a track model. Because of dense ionization, recombination dominates in the core giving insignificant free ions. In the time scale of observation, the $\delta$ rays mostly degenerate into ion pairs to which the Onsager probability is applicable. The electron thermalization distance is found to be 232 nm, the same as for $\gamma$ radiolysis and in agreement with Freeman (Phys. Rev. B, preceding Comment). Secondary electrons at energy about 200 eV can effectively penetrate the core.