Field ionization liquid argon

Mainly, this method is employed with ionization chambers filled with high mobility warm liquids or with liquid argon, krypton, or xenon. Since only the electronic component is observed, the pulse shape depends on the position of the ionizing particle track in the ionization chamber. Basically, two variants can be distinguished with a parallel plate ionization chamber (1) the track of the ionizing particle is parallel to the field lines or (2) the track runs perpendicular to the lines of field (Figure 32). 

Fission fragments produce dense ionization tracks from which electron escape is very low. Even at a field strength of 38 kV/cm, only 3% of the initial ionization is collected in liquid argon (Hitachi et al., 1987). 

A standard instrument in hi energy physics experiments is the liquid argon calorimeter with absorber plates from heavy metals (iron, lead, uranium). The liquid ionization chambers usually have electrode separations of 1 or 2 mm and operate at field strengths of several kV/cm. This leads to electron collection times in the submicrosecond time domain (Engler, 1984 Fabjan, 1985). Liquid argon of sufficient purity (oxygen impurity level approximately 1 ppm) from a storage tank is evaporated and recondensed into the calorimeter. No additional purification is necessary. 

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