Construction and 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 in direct contact with an array of lead plates used as the high voltage and ground planes. The transient response resulting from the passage of cosmic ray muons through the ion chamber was monitored for a period of 54 weeks to measure possible degradation of the signal due to contamination of the ionizing liquid that may have come from the lead plates. Over the first 17 weeks of the experiment, the loss of pulse height was measured to be less than 11 percent per year at 95 percent confidence. During the following 37 weeks, a more sensitive measurement was consistent with zero loss, or a limit of less than 2.9 percent per year at 95 percent confidence.