Speaker
Description
The India-based Neutrino Observatory (INO) collaboration is planning to build a 50 kiloton magnetized Iron Calorimeter (ICAL) to precisely study the atmospheric neutrino oscillation parameters. The collaboration has chosen Resistive Plate Chambers (RPCs) made up of float glass electrodes of 1.9 m × 1.8 m in area as the active detector elements and is going to deploy 28,800 of them in the ICAL detector. The RPCs will be operated in the avalanche mode with an optimized gas mixture of HFC−R134a/iso−C4H10/SF6 = 95/4.5/0.5. The experiment is expected to run for more than 10 years in order to record statistically significant number of neutrino interactions for the confirmation of atmospheric neutrino oscillation. Hence, long term stability and performance of the RPCs over the duration of the experiment is of prime concern. About 200,000 liters of gas is going to be circulating in the RPCs during the experiment. The gas lines running into about 135km in total are going to be supply/receive gas to/from the RPC detectors. In spite of stringent QC during the RPC gas gap making or gas lines plumbing, it is impossible to prevent ambient air or water vapor entering into the gas circuit over these long periods of time. The contaminants are known cause for serious degradation in the performance or permanent damage of RPCs. Considering the severe repercussions in the mammoth ICAL detector, a systematic study of this problem was undertaken. Two glass RPCs of 30 cm × 30 cm in size were fabricated and were simultaneously operated with dry gas mixture in one and with gas mixture along with controlled and calibrated amount of water vapor in the other. A common cosmic ray muon telescope was set up for studying both the RPCs. Ambient parameters such as temperature and relative humidity as well as RPCs' operating and performance parameters such as chamber current, noise rate, efficiency, charge collection per an event and time resolution for cosmic ray muon detection were systematically recorded throughout the experiment. It was observed significant degradation in the performance of RPC in which gas with water vapor was flown. Detailed studies were carried out to understand the causes and process of the degradation in performance of this RPC. These results will be presented.
