IONIZATION OF LIQUID ARGON BY X-RAYS - EFFECT OF DENSITY ON ELECTRON THERMALIZATION AND FREE ION YIELDS

Free ion yields were measured in liquid argon as a function of electric field strength at densities 736-1343 kg/m3 (temperatures 149-95 K). The field dependence of the yields was parametrized using the extended Onsager and box models. Over the present density range the total ion yield was constant within 1% and was taken as 4.4, the average of earlier values at 87-91 K. The absence of internal vibrational modes in argon makes its electron thermalizing ability smaller than that of methane. The electron thermalization distance b(GP) in liquid argon is 3-5 times longer than that in liquid methane at a given d/d(c)(d(c) = critical fluid density).