Analysis of Purity Probes H1 Liquid Argon Calorimeter

The sensitivity of our liquid argon purity measurement -around 0.03%- leads us to refine the tools used classically in this field. First we introduce an analytical form describing the spectrum of a 207Bi source for different values of purity and ionisation chamber gap. Second we analyse a surprising new effect: the variation of the ionisation yield of this source with the liquid argon temperature. Third we use our data to refine the charge collection models which relate electron recombination and attachment cross-sections to the electrical field.