1. (Santiago de Compostela-Spain)
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)

2. Detector used for tests
Same detector layout than in HADES tests (April-2003).
Gas mixture: % 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).
-Este es nuestro prototipo
-Definir RPC, 4 gaps, electrodos de aluminio
-Mezcla de gas

3. Sources used for tests
Na22 (~ 0.1 mCi) (mainly used for calibration)
Na22 (~ 1 mCi)
Co60 (~ 1 mCi)
2 x MeV collinear (positron annihilation)
1.274 MeV
1.173 MeV, 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 (!)

4. Temperature monitoring
Heating system
Temperature monitoring T1 T2 T3
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.

5. Trigger system used for tests
Efficiency trigger
Time resolution trigger
self-trigger mode
Coincidence with a 110 ps scintillator
RPC
scintillator
RPC
source
source L
Due to the high rate environment, coincidences by chance are dominant and must be suppressed with adecuate cuts.
Cauchy distribution

6. Temperature dependence
At constant Temperature
Gain (<Vgap>) Efficiency ε(<Vgap>) Time resolution σT (<Vgap>)
At non-constant Temperature
- The gas density decreases linearly with T.
- The glass resistivity decreases exponentially with T.
Gain (<Vgap>*) Efficiency ε(<Vgap>*) Time resolution σT (<Vgap>*)

7. Temperature dependence
Rate capability
<q> is in principle a function of <Vgap>* only:
If ΔV T/To is kept constant during measurements:

8. Temperature dependence
As a first approach, if the
reduced high voltage V* is
kept constant
‘Rate capability’: If the rate capability κ(T) increases
a factor n, the rate can be increased by the same
factor and the performance of the detector
remains unaltered.

9. + + Temperature dependence: A model for the efficiency
Average potential in the gap as a function
of the corrent drawn through the glass
Good aproximation if charge-space
effect is high +
Observed charge spectrum for γ primaries +
d is an overall constant

10. Efficiency measurements
Na22
Na22 + Co60
(2.5 cm further)

11. Efficiency measurements
X12
Increasing T
33 degrees

12. Time resolution measurements
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.
T=21 deg
Rate at center= 1.8kHz/cm2
After cuts 1 & 2

13. Time resolution measurements
Time resolution for gammas stands within 90 ps without significative dependence on primary rate. So it is hard to get the κ(T) factor from timing
measurements.
No significative dependence [!]

14. Ageing
T increase of 30 degrees

15. Geometric acceptance ≈ 87 %
Conclusions (I)
Results of april-03 at HADES
Geometric acceptance ≈ 87 %
HADES

16. Conclusions (II)
When the Temperature increases??
Rate capability
For 30 degrees increase no ageing
effects observed in 80 days!
measured
expected
Under study!

17. Geometric acceptance ≈ 87 %
Conclusions (III)
Geometric acceptance ≈ 87 %
for κ(T) measured
in 30 degrees increase