Cosmic ray tests of 7.6 m drift-tube counters and the readout electronics system of the venus muon detector

Eight-cell drift-tube modules of 7.6 m in length and the readout electronics system of the VENUS muon detector at KEK have been tested by using cosmic rays in order to evaluate the performance of the system. The cross section of each cell is 5x7 cm2. The anode wire is a gold-plated tungsten wire with a diameter of 70 μm. P10 gas (Ar/CH4 = 90/10) was used at 1 atm. Typical singles rates in the high voltage plateau region were about 220 Hz per wire which is slightly higher than the estimated cosmic ray rate of 150 Hz. The average dark current was about 6 nA per wire at an operating high voltage of 2.7 kV. The spatial resolution for a single tube has two distinct components. The main component contains about 96% of the total incident events and has an rms spatial resolution of about 1.3 mm. The second component has a much broader distribution with an rms value of about 12 mm. It is evident that these events are caused by delta-rays generated in the tube wall. The detection efficiency is essentially 100% if the two components are included. (orig.)