Transcript Resistive plate chambers for muon detection Waheed ahmad

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 coordinates 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 simultaneous 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
++++++++++++++++
Ionization
leads to
avalanche
HV
Gas
Resistive plate
Resistive plate
HV
Streamer
+++++
+++++ forms,
depletes
charge over
 (1-10mm2).
Field drop
quenches
streamer
+++++ + + +++++
HV

RPC rate capability
• 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.
  l   A 
  

 A  l 
  RC  
t~ 2sec
+++++++
--------
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 coefficient 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
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
Gas flow
Scale
Glass tube
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
Gluing
Leak test
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