Argon Purity Measurement of the d0 Calorimeter

The D0 Argon purity Test Cell (ATC) measures the O₂-equivalent pollution of a liquid argon sample extracted from the calorimeters. The cell consists in two radioactive sources, α (²⁴¹Am) and β (¹⁰⁶Ru), immersed in liquid argon which produce ionizations. Then, the created charges are drifted by an adjustable electric field. Due to absorption of e^- by electronegative impurities, the total collected charge depends on the O₂ pollution. The device is an upgraded version of Run I D0 ATC. Its present sensitivity is estimated to be better than ± 0.15 ppm.

A pulser with adjustable frequency is used to calibrate the electronics. The electric field is ramped step by step between 5 kV cm^-1 and 15 kV cm^-1. Furthermore, for calibration purpose, the ATC is equipped with a system to pollute a pure Argon sample, with a given amount of O₂.

The setup and method of analysis of α and β measurements will be described. Measurements of the purity of the gas Argon from the three calorimeters (Central, North and South End Cap) will be presented.