A Sealed Metal Argon Ionization Chamber (Argonion)

The design, construction and performance of a sealed all metal, transmission type argon ionization chamber (Argonion) and its associated electronics is described. It exhibits a linear response to charged particle density fluxes in the range of 105 - 1011 cm -2 s -1 and has very good long term stability. Calibration of the chamber at low fluxes can be made against scintillation counters and at high fluxes against secondary emission chamber and foil activation techniques. Because it bridges the intermediate range, the Argonion is extensively used in high intensity experiments in the CERN PS and SPS secondary beams. It consists of a stainless steel cylinder, two thin end windows (25 μm stainless steel), 21 parallel electrodes (2 μm aluminium) and is filled with pure argon slightly above atmospheric pressure. The chamber introduces a total mass (windows and electrodes) into the beam of "' 50 mg cm-2 equivalent iron (~ 0.4% of the iron radiation length). The introduced mass of the argon is ~ 50 mg cm -2 or ~ 0.25% of the argon radiation length.