A new gas mixing system for MWPC operation

A simple system is described which permits the admixture of a very small proportion of an electronegative impurity gas (typically approximately equal to 0.1% of a freon) to otherwise pure isobutane for use in complex multiwire proportional counters containing thousands of anode wires and square metres of cathode area. The gas system described has permitted many hundreds of hours of stable operation in such detectors during the clinical trials of the Rutherford Appleton Laboratory Positron Camera. (author)