Diapositiva 1

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High rate capability of ordinary glass RPCs
Diego González Díaz (Santiago de
Compostela-Spain)
A. Blanco, P. Fonte, L. Lopes, R.
Ferreira-Marques (LIP-Coimbra)
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• Same detector layout than in HADES tests
  (April-2003).
• Gas mixture 80 C2H2F4 20
  SF6 .
• Normal window glass, 2 mm thick.
• 4-gaps, 0.3 mm thick.
• Aluminum electrodes, 2 mm thick.
• Shielding boxes.
• BGA2712 amplifier.
• Reference BICRON scintillator (110 ps for
  gammas).

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Na22 ( 0.1 mCi) (mainly used for
calibration) Na22 ( 1 mCi) Co60 ( 1 mCi)
2 x 0.511 MeV collinear (positron annihilation)
1.274 MeV
1.173 MeV, 1.332 MeV (opposite directions but not
perfectly collinear)
Interaction occurs through Compton scattering in
the electrodes. The electron scattered ionizes
the gas and is detected. Charge distribution and
time resolution are different from MIPS (!)
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RPC box is rolled in a coating that provides
uniform heating
Temperature is measured on-line through the
voltage drop on PT100 sensors placed in front,
behind and in the middle of RPC cell.
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Coincidence with a 110 ps scintillator
self-trigger mode
RPC
RPC
scintillator
source
source
L
Due to the high rate environment, coincidences by
chance are dominant and must be suppressed with
adecuate cuts.
Cauchy distribution
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At constant Temperature
Gain (ltVgapgt) Efficiency e(ltVgapgt)
Time resolution sT (ltVgapgt)
At non-constant Temperature
- The gas density decreases linearly with T.
- The glass resistivity decreases exponentially
with T.
Gain (ltVgapgt) Efficiency e(ltVgapgt)
Time resolution sT (ltVgapgt)
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Rate capability
ltqgt is in principle a function of ltVgapgt only
If ?V T/To is kept constant during measurements
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As a first approach, if the reduced high voltage
V is kept constant
Rate capability If the rate capability ?(T)
increases a factor n, the rate can be increased
by the same factor and the performance of the
detector remains unaltered.
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d is an overall constant
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1-Tof window of 1 ns (cut random
coincidences). 2-Events of good quality
in reference scintillators (large amount of light
collected).
3-Cut in the peak of the position distribution.
T21 deg Rate at center 1.8kHz/cm2
After cuts 1 2
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No significative dependence !
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Results of april-03 at HADES
Geometric acceptance 87
HADES
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When the Temperature increases??
Rate capability
For 30 degrees increase no ageing effects
observed in 80 days!
Under study!
measured
expected
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Geometric acceptance 87
for ?(T) measured in 30 degrees increase