Glass Resistive plate chambers for muon Detection Waheed Ahmad Dar University of Kashmir

Introduction Particle Detection: Various tasks to be carried out for particle detection methods. -Localization of charged particle trajectories i.e. measurement of space co- ordinates and directions. -Measurement of charge and momentum. This is achieved by determing the trajectory of each particle. -Determination of particle mass which is achieved by a simul- taneous measurement of momentum and energy or momentum and velocity. -Determination of energy, direction and nature of a neutral particle. There are broader classes of particle detection methods -Non- destructive Methods: These methods allow multiple measurements to be performed without changing the identity of the detected particle. The basis of the method are the electromagnetic interaction of charged particle with matter. -Destructive Methods: These methods destroy the particles identity during its detection. These are mostly used for the detection of neutral particles.

Resistive plate chambers They are special type of ionization detectors made up of high resistive plates having resistivity of the order of 2x1012 ohm cm. Gas gap of 2mm between the two glass plates, having width of 3mm of each glass plate with graphite coating on their outer surfaces. High resistive plate chambers help us to contain the discharge by the passage of the charged particle or an ionizing the radiation in gas volume. Pick up strips are used to collect the signal. Typical time resolution is of the order of 1-2 ns.

Basic design Resistive Plate Chamber

Diagram of RPC

Significance of RPC Built from simple and common material. The cost of RPC is much smaller as compared to other scintillators. It is easy to construct and operate. Simple signal pick up and readout system. High efficiency of the order of >90% and the time resolution of the order of ~1ns. Two dimensional readout (x and y). Long term stability.

Motivation of the present work RPC is a key element when it comes to muon detection. RPC is used successfully in Belle experiment at KEK and BABAR experiments. Presently the RPC will be studied as the particle detector for iron calorimeter for India based Neutrino observatory (INO).

Basic principle of gaseous ionization detectors. The gaseous ionization detector consists one gaseous chamber whose two opposite faces having conducting material. The two glass plates is applied with a high voltage of ~10KV . When a sufficiently energetic radiation passes through the chamber, it ionizes the gas molecules and produces a certain number of electron ion pairs. The mean number of electron ion pairs created is proportional to the energy deposited on the chamber. With the application of strong electric field, the electrons are drawn towards the anode and ions are drawn towards the cathode and gets collected . If the electric field is strong enough, the free electrons are accelerated to enough high energies where they are capable of ionizing the gas molecules in the chamber. The electrons liberated in this secondary ionization then accelerated to produce still more ionization and so on. This results in an ionization avalanche or cascade .This is known as avalanche mode of Resistive plate chamber.

(contd..) Basic principle of gaseous ionization detectors The avalanche has the form of a liquid drop with electrons grouped near the head and slower ions tailing behind. When such an avalanche increases in number, they form a streamline of continuous flow of charges from one electrode to the other . This forms a streamer pulse which are collected by the front end electronics.

Principle of operation of Resistive plate chamber  Charge depletion induces signal. Charge depletion fixed by geometry, resistivity, gas. Dielectric Resistive plate Resistive plate Resistive plate Streamer forms, depletes charge over (1-10mm2). Field drop quenches streamer ++++++++++++++++ +++++ +++++ +++++ + + +++++ Ionization leads to avalanche HV HV HV  Gas 

RPC rate capability             l A RC The advantage of the high resistivity of the glass plate is that ,it localizes the drop in the high applied voltage. The dead time for the detector is due to the time necessary to the voltage tension at the gas gap, but will concern only a small area of the detector surface. t~ 2sec +++++++ +++++++ ------------ --------              l A RC

Resistance measurement of 2mx2m RPC

Gas system The choice of filling the gas system is governed by several factors: low working voltage, high gain, good proportionality and high rate capability. For minimum working voltage, the noble gases are usually chosen, as they require low electric field intensities for avalanche formation. Hence the role taken by the gas mixture is very important, as the first ionization potential, the first Townsend co-efficient and the electronegative attachment co-efficient determines the avalanche multiplication. The gas mixture fixes the working mode of the RPC in avalanche mode or in streamer mode.

Gas system (contd..)‏ To work in a streamer mode, the main components should provide a robust first ionization signal and a large avalanche multiplication for a low electric field. One typical element can be Argon. To work in an avalanche mode the main components could be an electronegative gas, with high primary ionization but with small free path for electron capture. The high electronegative attachment co- efficient limits the avalanche electron number. Tetrafiuorehtane (known as Freon), which is widely used. But here we use R134A(as Freon) which is eco-friendly. The other gas is isobutane which is having high probability for absorbing ultra violet photons. This is known as quenching gas. Finally SF6 is used to control the excess number of electrons . R134A(Freon) = 95.4, Iso-butane = 4.3, SF6 = 0.3

Avalanche and Streamer pulses Taken by CRO Avalanche pulse Streamer Pulse

High voltage verses Current with and without SF6

Flux = (change in volume)/ (Change in time) Calibration of the MFC The gas is fluxed into the tube and then water is allowed to flow through the tube. The gas apply the pressure on the water and water bubble flows through the tube and we can determine the rate of flow by measuring the change in volume in some fixed time with the help of stop watch. Flux = (change in volume)/ (Change in time) Water flow Glass tube Gas flow Scale

Calibration plots of MFC for Iso-butane, R134A and SF6

(Contd..) Calibration plots of MFC

Calculation of gas flow rates As per the reading displayed in the gas system. Freon = 15.8 sccm Iso-butane = 0.65 sccm SF6 = 0.12 sccm After correcting the value from the Calibration curve Freon = 15.478 sccm Iso-butane = 0.695 sccm SF6 = 0.046 sccm Total amount of flow rate(Freon+iso-butane+SF6)= 16.22 SCCM Hence each RPC (1mx1m and2mx2m)gets an average of = 8.11 SCCM

RPC efficiency We measure the efficiency of RPC by making the experimental setup in such a way to ensure that the trigger pulse is soly due to atmospheric muons , to do that we have to exclude all other cosmic rays which forms the noise. We set up the experiment as shown in fig below. Here we use six scintillators P1 to P6. we kept 2cm paddle i.e. P5 along the main strip and two 20cm paddles i.e. P3 and P4 are wide veto paddles on the two sides of paddle P5, while as the other three paddles i.e. P1,P2 and p6 are kept below 2mx2m RPC above one another. This ensures us that muon trigger is generated when we have four paddles in coincidence and other two in anticoincidence. Efficiency of RPC = (4-fold x veto x RPC) / (4-foldxveto)‏

RPC efficiency

QDC and TDC plot for the main strip

Different phases of construction of RPC Graphite Painting Spray Gun Glass Cleaning Resistance measurement

(contd..) Different steps of construction of RPC Leak test Gluing

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