Anode wire swelling—a possible phenomenon in anode wire aging under high-accumulated dose

We present results from an aging investigation of straw drift tubes placed under sustained irradiation from an 90Sr (2 Ci) β-source. A thorough study of the aging phenomenon of the gold-plated tungsten wires with an accumulated charge of 9 C/cm was performed. Aging tests were performed with a gas mixture containing Xe, CO2 and CF4. As a result of the aging process, the gold coating on the wires was damaged, and the wire diameter increased from 35 to 42 μm. This phenomenon of anode wire swelling by forces applied from within the anode wire is a possible new aging mechanism. We show that this anode swelling effect can be explained by production of tungsten oxidation in the wire. Using Nuclear Reaction Analysis (NRA), in combination with an SEM/XEM analysis, it is determined that deposits containing tungsten and oxygen are distributed along the wire corresponding to the gas flow direction. The concentration of oxygen as a function of depth within the wire has also been investigated using NRA, and it is shown that oxygen transportation into the depth of the wire occurs.