diego gonzalez diaz university of santiago de compostela diego gonzález díaz (santiago de...
TRANSCRIPT
Diego Gonzalez Diaz University of Santiago de Compostela
Diego González Díaz
(Santiago de Compostela-Spain)
A. Blanco, P. Fonte, L. Lopes, R. Ferreira-Marques
(LIP-Coimbra)
Diego Gonzalez Diaz University of Santiago de Compostela
Detector used for tests
- 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).
Diego Gonzalez Diaz University of Santiago de Compostela
Sources used for tests
Na22 (~ 0.1 mCi) (mainly used for calibration)Na22 (~ 1 mCi)Co60 (~ 1 mCi)
2222
2222
*
*
NeNe
eNeNa e 2 x 0.511 MeV collinear (positron annihilation)
1.274 MeV
5959
5960
*
*
CoCo
eCoCo e1.173 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 (!)
q
qq ped
eqdq
dN)(
1
Diego Gonzalez Diaz University of Santiago de Compostela
Temperature monitoringHeating system
RPC box is rolled in a coating thatprovides uniform heating
T1
T2
T3
Temperature is measured on-line through the voltage drop on PT100 sensors placed in front, behind and in the middle of RPC cell.
Diego Gonzalez Diaz University of Santiago de Compostela
Trigger system used for tests
Efficiency trigger Time resolution trigger
source
Cauchy distribution
20
/12
1
Lx
N
Ldx
dN
L
RPC
self-trigger mode
source
RPC
Coincidence with a 110 ps scintillator
scintillator
Due to the high rate environment, coincidences by chance are dominant and must be suppressed with adecuate cuts.
Diego Gonzalez Diaz University of Santiago de Compostela
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.
At constant Temperature
0
)]([*T
TTRIVVgap
Gain (<Vgap>*) Efficiency ε(<Vgap>*) Time resolution σT (<Vgap>*)
RIVVgap
Temperature dependence
Diego Gonzalez Diaz University of Santiago de Compostela
)()(*
00 TTR
q
T
TVVgap
)(*
FVgap
0
)]([*T
TTRIVVgap
]/[ 2cmkHzqI
1
00
))(
)(()(
T
T
TR
TRT Rate capability
<q> is in principle a function of <Vgap>* only:
Temperature dependence
If ΔV T/To is kept constant during measurements:
Diego Gonzalez Diaz University of Santiago de Compostela
)(
)(
TT
1
00
))(
)(()(
T
T
TR
TRT
‘Rate capability’: If the rate capability κ(T) increasesa factor n, the rate can be increased by the samefactor and the performance of the detectorremains unaltered.
oT
TVV *As a first approach, if the
reduced high voltage V* is kept constant
Temperature dependence
Diego Gonzalez Diaz University of Santiago de Compostela
Temperature dependence: A model for the efficiency
q
q
pedth
th
edqdq
dN)(
)(Td
obs e
)(Td
e
)()(*
00 TTR
q
T
TVVgap
Average potential in the gap as a function of the corrent drawn through the glass
qaVgap *
Good aproximation if charge-space effect is high
+
q
qq ped
eqdq
dN)(
1
Observed charge spectrum for γ primaries
+
d is an overall constant
Diego Gonzalez Diaz University of Santiago de Compostela
Efficiency measurements
Na22
Na22 + Co60
Na22 + Co60
(2.5 cm further)
)(Td
obs e
Diego Gonzalez Diaz University of Santiago de Compostela
Efficiency measurements
1
00
))(
)(()(
T
T
TR
TRT
X12
)(Td
e
Increasing T
33 degrees
Diego Gonzalez Diaz University of Santiago de Compostela
1-Tof window of 1 ns (cut random coincidences). 2-Events of good quality in reference scintillators (large amount of light collected).
After cuts 1 & 2
3-Cut in the peak of the position distribution.
Time resolution measurements
T=21 degRate at center= 1.8kHz/cm2
Diego Gonzalez Diaz University of Santiago de Compostela
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 signific
ative dependence
[!]
Diego Gonzalez Diaz University of Santiago de Compostela
Ageing
T increase of 30 degrees
Diego Gonzalez Diaz University of Santiago de Compostela
Geometric acceptance ≈ 87 %
2
2
/100%5.1
/1007.467
cmHz
cmHzpspsT
Results of april-03 at HADES
Conclusions (I)
HADES
Diego Gonzalez Diaz University of Santiago de Compostela
2
2
/100)(
%5.1
/100)(
7.467
cmHzTK
cmHzTK
pspsT
When the Temperature increases??
1
00
))(
)(()(
T
T
TR
TRT
Rate capability
For 30 degrees increase no ageing effects observed in 80 days!
deg6
2)(
T
deg9
2)(
T
measured expected Under study!
Conclusions (II)
Diego Gonzalez Diaz University of Santiago de Compostela
Geometric acceptance ≈ 87 %
for κ(T) measured in 30 degrees increase
Conclusions (III)