diego gonzalez diaz university of santiago de compostela diego gonzález díaz (santiago de...

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)


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).


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


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.


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.


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


)()(*

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:


If ΔV T/To is kept constant during measurements:


)(

)(

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: A model for the efficiency

q

qq

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


Efficiency measurements

Na22

Na22 + Co60

Na22 + Co60

(2.5 cm further)

)(Td

obs e


Efficiency measurements

1

00

))(

)(()(

T

T

TR

TRT

X12

)(Td

e

Increasing T

33 degrees


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


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

[!]


Ageing

T increase of 30 degrees


Geometric acceptance ≈ 87 %

2

2

/100%5.1

/1007.467

cmHz

cmHzpspsT

Results of april-03 at HADES

Conclusions (I)

HADES


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)


Geometric acceptance ≈ 87 %

for κ(T) measured in 30 degrees increase

Conclusions (III)

diego gonzalez diaz university of santiago de compostela diego gonzález díaz (santiago de...

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