Study of aging properties of a wire chamber operating with high-pressure hydrogen

The project for a precision measurement of the μp-capture rate (μCAP experiment) is based on an application of a multi-wire proportional chamber (MWPC) operating in ultra-pure hydrogen at 10bar pressure. A special test setup was constructed at PNPI to investigate the MWPC performance under the expected experimental conditions. The aging studies of the MWPCs were performed with intense irradiation from an α-source (241Am) and a β-source (90Sr). After 45 days of continuous irradiation by α-particles no changes in the currents, in the signal shapes, and in the counting rates were observed. It was demonstrated that the MWPCs can operate without degradation at least up to accumulated charges of 0.1C/cm wire. These irradiation conditions are much more severe than in the real experiment. During the study of the MWPC we have observed an appearance of short duration signals with amplitudes an order of magnitude larger than those of normal signals from the α-particles. The number of such signals (“streamers”) strongly depend on HV. We shall continue these tests in the future with the goal of obtaining more detailed information about aging properties of MWPCs operating with high-pressure hydrogen.