Light Output Uniformity of Long CsI(Tl) crystals -

the “bottle-neck” for gamma and proton spectroscopy

C sI (T l ), 20x20x100 + A P D

K har ' kov, 05 St. G obain, J 701

D istance form C sI fr ont face

C hannels

C hannels

dL/L

Cou

nts

Cou

nts

C o60 C o60

C s137 C s137

9. 4%

12. 2%

%

16. 0%

0. 96

0. 98

1

1. 02

1. 04

0 2 4 6 8 10

0. 96

0. 98

1

1. 02

1. 04

0 2 4 6 8 10

0

250

500

750

1000

200 400 600 800 10000

250

500

750

1000

200 400 600 800 1000

0

500

1000

100 200 300 400 5000

500

1000

100 200 300 400 500

Light Output Uniformity for CsI(Tl) as supplied by manufacturers…

…and Energy Resolution for gammas, measured by a APD ( 5x5), when irradiating the whole crystal volume…

*

CsI(Tl), L=110 mm

source

20x20

Lund-Dubna, VC_2007_12_13

L=110 mm

D istance along C sI , mm50 100

Ligh

t var

iatio

n, d

L/L

1. 0

0. 95

0. 90

a) dL /L = 0. 0%

b) dL /L = 5. 0%

c) dL /L = 10. 0%

a)

b)

c)

P roton E nergy, M eV

Ligh

t Out

put (

arb

. un

its) dL O = 3. 6%

dL O = 0. 0%

dL O = 1. 75%

3000

3500

4000

4500

5000

5500

100 120 140 160 180 200

Effect of crystal Light Output nonuniformity ( a)- 5%, b)-10% on the Light collected by Photodetector.

Calculated for Protons.

For Gammas – the picture looks similar, but with energy scaled by factor 1/4 - 1/5 .

Conclusion – dLO/LO must be less than 1% along the length of crystal

Straggling and Nonlinearity for Protons and Gammas due to dL/L

Lund-Dubna, VC_2007_12_13

2007/12/11 18. 15

5

L = 110 mmC sI (T l )

20x2

0

23x2

3

L=11

0 m

m

Ene

rgy

Res

olut

ion,

%

C hannels

E nergy, M eV

Source

5. 6%

1. 17 M eV

1. 33 M eV

M easured by P D , 10x10

by A P D , 5x5

by A P D , 10x10

0

200

400

600

800

1000

1200

1400

1600

200 400 600 800 1000 1200 1400

1

10

10-1

1

Test with highly uniform in Light Output Crystal , L=110 mm, dL/L <0.7%

CsI(Tl) – 20x20 – 110 – 23x23 mm**3

Irradiated for 110 mm distance…

Photodetectors:

PD – 10x10 mm**2

APD – 5x5 mm**2 / <M>=40

APD – 10x10 mm**2 / <M>=50

Our data… compare APD of 5x5 and 10x10 mm**2 !!!!

Published data,

10x10x10 mm**3 CsI(Tl)+ 10x10 APD!!!

Lund-Dubna, VC_2007_12_13

C hannels

P ulser1. 17 M eV1. 33 M eV

A P D , 10x10C sI (T l )

C sI (T l )A P D , 5x5

P ulser

V M 2000(refl ector )

S_ A P D / S_ L ighG uide= 1.

S_ A P D / S_ L ighG uide = 0. 25

L (5x5)/L (10x10)= 0. 65

0

100

200

300

400

500

200 400 600 800 1000 1200 1400

0

100

200

300

400

500

600

200 400 600 800 1000 1200 1400

a)

b)

Effect of VM200 ( ESR) Light Guide reflector on Light collection and Energy Resolution

a) - Active area of APD = Active area of Light Guide, 10x10 mm**2. S_APD/S_LG =1.0

b) - Active area of APD = 0.25 of Active area of Light Guide, 5x5 mm**2.

S_APD/S_LG =0.25

Light Collection coefficient,

L(5x5)/L(10x10) = 0.65, due to the VM2000

(ESR) reflector, covering an extra surface

By using an APD of 10x10 mm**2 we can gain around 12% in the energy resolution as compared with the APD of 5x5 mm**2

Lund-Dubna, VC_2007_12_13

Some Conclusions and Plans for Future R&D

Lund-Dubna, VC_2007_12_13

1. Light Output uniformity for Long crystals is more important than the active area of the APD2. For the highly uniform in L.O. crystals we can get almost ideal Energy Resolution3. New groups must be involved in the Uniformity Problem for real Califa geometries

Plans for nearest future:

1. Light Uniformity adjustment for the real CALIFA crystal geometry

2. Tests with APD’s, PMT’s / like R7400U-3, 20 – insensitive to magnetic field

3. To mount CsI(Tl) “demonstrator” for bench and in-beam tests