Transcript New Technology of Making Resistive Plate Counters Without

New Technology of Making
Resistive Plate Counters
Without Linseed Oil Treatment
Jiawen ZHANG
8/18/2004
Introduction
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Resistive Plate Chambers (RPCs) have excellent time
resolution. Currently, more large experiments are building
RPC based detector systems.
The surface quality is the most parameter of bakelite plates,
it affects the performance of RPC. In order to threat the
inner surfaces, one method is treated with linseed oil,
another is use glass as resistive plate material.
Based on the operational experiences of the Babar RPC
systems and the problems associated with linseed oil
coating, we decided to investigate new approaches for
constructing RPCs when we started to consider the design
of the muon identifier for the BESIII.
New Resistive Plate
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We have made some key advances since we started this
project two years ago. The most important innovation is a
method to improve the surface smoothness(~200nm) and
control resistivity(109 -1014 Ω·cm ) when the resistive
plates are produced in the factory.
The surface of our resistive plates is covered by a layer of
specially formulated plastic film. The prefabricated film
laminated onto the surface of the phenolic paper plate
during the high pressure lamination process can reduce the
surface defects caused by the steel plates used in the
lamination process. The thickness of the film is 50 m and
the resistivity of the resistive plates can be adjusted to
optimize the performance of RPCs.
RPC prototypes
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The resistive plates produced by a local lamination plant
were assembled into RPCs. The bulk resistivity of the
resistive plates used for constructing this prototype RPC
was about 91011 Ω·cm measured at 20 oC. The
thickness of the two resistive plates was 2 mm and the
gap size was also 2 mm. Spacers and edge frames were
glued between the two electrode surfaces.
Test system
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we use 3 scintillator detectors
as RPC trigger signal. A
computer controls the system,
therefore the tests are
completely automatic.
Electronic system is partially
NIM, while CAMAC and
personal computer control
system are used for the data
collection and the high voltage
control.
Performance of prototypes
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The test results described in this section lasted several days
from the end of May to the beginning of June 2004. The
chamber gas mixture was an Ar/C2F4H2/C4H10, The
temperature of our lab was 20 oC to 28 oC, the RPC
efficiency is not significantly affected by the temperature.
But changes in lab temperature can cause some minor
irregularities in our dark current and singles rate data. the
signals amplitudes increased almost linearly with the high
voltage from about 200 mV at 7 kV to about 840 mV at
9.4k V.
For RPCs working in a low counting rate environment, the
efficiency level on the efficiency plateau, the length of the
efficiency plateau, the dark current and the noise rate are the
most important parameters to judge their performance.
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0.9
0.8
0.6
50mv
0.5
100mv
0.4
150mv
200mv
0.3
250mv
0.2
0.1
0
6000
6500
7000
7500
8000
8500
9000
9500
High Voltage (V)
900
800
Averge Pulse Height (mV) aa
Efficiency
0.7
700
600
500
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300
200
7000
7500
8000
8500
High Voltage (V)
9000
9500
Long term behavior
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The prototype RPCs were monitored from June 2003 to
July 2004, and were placed near a target in the electron test
beam at IHEP from October 2003 to March 2004 and were
exposed to scattered electrons. Dark currents and counting
rates were monitored during this radiation test. The
efficiencies of the RPC prototype reached 96 to 98% at 8
kV from the beginning of the test and remain high
thereafter. The dark current was less than 10 μA/m2 at the
start of the test and dropped to less than 1 μA/m2 in about 4
weeks, the singles counting rates at 100 mV threshold
reduced from approximately 0.2 Hz/cm2 to 0.05 - 0.06
Hz/cm2 after the initial training period.
The dark currents and counting
rates of the prototype RPCs
increased during the neutron
radiation test and recovered to the
level before the neutron radiation
in about 10 days after the radiation
exposure.
)
High Voltage(V)
Single Counting rate (Hz/cm^
Efficiency
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Before Radiation
After Radiation
Before Rad
After Rad
High Voltage(V)
Can be seen in this Fig. the behavior of the prototype
RPC was not significantly changed after the electron
radiation exposure.
Product
400m2 RPCs have been manufactured.
The throughput is 10m2 per day.
The eligibility rate of products is more than 95%.
Before training
The efficiency plateaus started from approximately 7.0 kV,
When HV= 7.5kV
more than 90% RPCs’ efficiencies are more than 95%
More than 92% RPCs’counting rate are less than 0.6Hz/cm2 .
More than 80% RPCs’ dark current are less than 25μA/m2.
Dark current at 7.5kV (μA/m2)
Counting Rate at 7.5kV (Hz/cm2)
Statistic result of the RPC
without training
Efficiency at 7.5kV
Conclusion
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The prototype RPCs for the BESIII spectrometer
manufactured by using a new type of resistive electrodes
that we developed showed very promising performance
without the conventional linseed oil treatment. The BESIII
RPC prototypes had high efficiency, long plateau, low
singles counting rate and dark current.
After a fairly long training period, the dark current dropped
to the level of less than 1 A/ m2 with our operating gas in
the streamer mode and the singles counting rate reached
the level below 0.1 Hz/cm2. The performance of the RPC
prototypes has been quite stable over a period of one year.
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