Wire Chamber Aging and Wire Material

Recent studies on wire chamber aging has shown surprising results indicating that anode wire material may have a strong influence on the useful life-time of a chamber or counter. The aging process discussed here is related to changes in the surface characteristics of the anode wires. Those changes may be due to an oxidation process involving molecules produced from the dissocation of organic quenching agents during the avalanche process. It is observed that after some running time the anode wire surface is coated with a nonconductive film, which drops the electric field around the anode wire, reducing the gain as the aging process continues. Aging due to polymerization and other processes have been known since the early years of Geiger and proportional counter operation. Interesting phenomena found here shows that the aging process is not only dependent on the gas mixture, it is strongly related to the anode material. Results reported earlier showed that chambers with gold plated tungsten anode wire using Argon-Ethane-Ethyl alcohol gas mixtures performed well for a very long time. They showed no appreciable loss of gain after an accumulated charge of one to two Coulombs per centimeter of wire length. There was no evidence of polymerization. Aging was accelerated when the gold plated tungsten anode wire was replaced by Stablohm-800 resistive alloy (75% Ni + 20% Cr + Al + Cu) wire using the same gas in the same chamber.