Operation of an ion chamber consisting of lead plates immersed in 2,2,4,4 tetramethylpentane

A small test ion chamber has been constructed using 2,2,4,4 tetramethylpentane as the ionizing liquid and an array of lead plates as the high voltage and ground planes. Signals resulting from ionization deposited in the ion chamber by cosmic-ray muons were monitored for possible degradation from contamination that may have come from the lead plates. At the 95% confidence level, the loss of pulse height was measured over the first 17 weeks of the experiment to be less than 11% per year. A more sensitive measurement over the following 37 weeks was consistent with zero loss, or a limit of less than 2.9% per year at 95% confidence.