Leak test of Resistive Plate Chamber gap by monitoring absolute pressure

The India-based Neutrino Observatory Project (INO) is a proposed underground high energy physics experiment at Theni, India to study the neutrino oscillation parameters using atmospheric neutrinos. The 50 kton magnetised INO-ICAL detector will require approximately 30,000 of 2 m x 2 m Resistive Plate Chambers (RPC) as sensitive detectors and proposed to operate for about 20 years. For success of the experiment, each of the RPCs has to function without showing any significant aging during the period of operation. Hence, various tests including a proper leak test are performed during and after production. The methods of leak rate calculation using conventional manometer are valid only when both the volume of the test subject and ambient pressure are kept constant. But both these quantities for a RPC gas gap depend widely on the ambient pressure and temperature. A proper quantitative estimation of the leak rate cannot be acquired from such pressure measurements. By monitoring the absolute pressures, both outside and inside of an RPC, along with the temperature, its leakage rate can be estimated. During the test period, the supporting button spacers inside an RPC may get detached due to manufacturing defect. This effect also needs to be detected.