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CeF3(Ba) radiation hard scintillator for electromagnetic calorimeters
Nuclear Instruments and Methods in Physics Research A313 (1992) 340-344 North-Holland
NUCLEAR INSTRUMENTS &METHODS IN PHYSICS RESEARCH
Section A
a) radiation hard scintillator for electromagnetic calorimeters A.A. Aseev, E.G. Devitsin, V.A. Kozlov, Yu.I . Hovsepyan, S.Yu. Potashov, K.A. Sokolovsky and .V. Uvarova P.N. Lc bedev Physical Institute o f the Academy of Sciences of the USSR, Moscow, USSR V.G. Vasilchenko
Institute for Nigh Energi, Pltysicv, Prowino, USSR Received 28 August 1991
The influence of divalent fluoride dopants BaF.,, CaF 2 , SrF2 on radiation and luminescent properties of CeF; crystal is studied. A high radiation hardness ( > 10 8 rad) has been obtained for CeF., crystals doped with BaF, .
1. Introduction
In connection with new experimental tasks, which are to arise at future accelerators, the problem of creation of fast radiation hard crystals is emerging. It is a common knowledge that calorimeter elements must withstand dose rates of about 107 rad/yr and more. In addition, calorimeter radiator materials must have a short radiation length and a small Molière radius. In refs. [1-5] it is pointed out that a heavy inorganic scintillator CcF3 seems rather promising for applications in e.m. calorimetry of future accelerators due to its short decay time and huge light yield. Table 1 shows the main characteristics of CeF; (pure) [1]. Radiation hardness of CcF; (pure) has been alreadv investigated [3-5]. 2. Technique In current work the radiation and luminescent properties of CcF3 doped with BaF,, CaF,, SrF, up to 1.5% (by weight) are studied . The synthesis of CcF; monocrystals doped with Ca, Sr, Ba was performed with the help of specially prepared mixture for the growth in accordance with a technological scheme, consisting of sequentially following operations of multiple impregnation of the material by fluorine with the purpose of its full refinement from oxygen mixture . The crystal growth was carried out by the vertically directed crystallization technique (Bridge an-Stockbarger method) in the fluorine environment .
Decay times of CeF3 crystals were investigated using a delayed coincidence technique [5]. Samples of 1 cm in diameter and 5 mm thick, irradiated by "7Cs, were placed in a steel tube with two photomultipliers (PMT-71) with quartz windows on both sides. The samples were optically coupled to START PMT with a help of silicon grease (Rhodorsil) . The STOP PMT, situated at a distance of 10 cm from the crystal, operated in a photon counting mode. This setup is capable of measuring decal , times of up to 100 ns with 1 ns resolution . 3. Results For example some of the obtained scintillation decay curves are presented in figs. la-ld. The curves were fit by an exponential dependence in order to get decay constants. For the slower component the results are provided for different divalent fluoride dopants in table 2. Table, i The main characteristics of CeF; (pure) [1] Density [g/cm;] Radiation length [cm] Molière radius [cm] Decay constant [ns] Peak emission [nm] Index of refraction Light yield [%] (Nal(TI) = 100%) Hygroscopie
0168-91)02/92/$05 .00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
6.16 1 .7 2.72 5(short), 300ong) 310 (short), 340 (long) 1 .68 4-5 No
A.A . Aseev et al. / Cel"ffa) radiation hard scintillator 1()000
341
CeP3(f'ure)
Coil 11 Us
1:
'
S~-int
time '12 !) fr .-,
""ea e
e
e fes
ue
ee e e H, 'eNa " ,e
1()0
ee e
0
loooo
ee,e,e,e
20
40
60
e " e e e
80
Tinte Cris]
Counts
aa
1011
CeF3(Ba 0.67%)
M
Scint. time 28 3 ns
1000 ~
s
100 a
io l_ _-_ -_ 0
20
40
e
e
"aa
ee
e®
e
1000
e a
e
" ea
Scuit
time 28 2 ns
s ee
aa eee e e a
am,
s
100
100
CE , F:3((%3 0 .25-:1 '
e
--
80
Time [ns]
Counts e
- ______-_ I---
60
e
mo
ee ae ",
s ° ae s e e e a s
e
°
®
ee
m
e ee s ,w °"e e
e a , ms
101 0
1
20
-I
__-
40
L
-
60
Time [ns]
J_ 80
100
Fig . 1 . Scintillation decay curves of CeF3 (pure) and CeF; + dopants with quartz PMT at room temperature .
A.A . Astvt, et al. / CeF j%d radiation hard scintillator
342
()
Count-8
100001
,
~d)
h me 27 0 iv,
e
10
(i()
'l'it))o (lis l Fig. 1 . (continued) .
Only statistical errors are shown . It is clear that such a doping leads to a decrease in the decay constant from 32.9 ns for CcF; (pure) to 27.0 ns for CcF3 (0.12% Sr). The light output of CeF; doped with divalent fluorides was measured by comparing its response to 0.662 MeV photons ("'Cs) to that of a pure CeF3 crystal under the equal experimental environment . The CcFj (with dopants) samples of the same size were enveloped with a reflective Teflon tape and optically coupled to a quartz window PMT. For each sample under investigation there was obtained a photopeak corresponding to the 0.662 MeV photon in pulse height spectrum . The results are provided in table 2. It is clear that with such an amount of dopants light output falls down to 62.2% for CeF3 (1.48% Ca). There also have been performed some measurements of radiation hardness of CeF 3 (with dopants) crystals by exposing them to 1 .2 x 10 7 rad and 10 8 rad of -y-rays of 61) Co at the rate of 330 rad/s. The light transmission of crystals was measured before and after irradiation (figs. 2a-2d). A reduction in transmission of = 11% was obtained for CcF; (pure) in peak emission spectra (340 nm) after an exposed dose of 1.2 x 10 7 rad . Such a reduction for CeF,(Ca) and CeF3(Sr) reached = 5% for the same dose. There was no reduction in transmission spectra for CeF3 (Ba) after the dose of 1 .2 x 107 rad and small reduction for 10' rad . Fig . 3 illustrates simulated by the GEANT3 Monte Carlo program radial shower profiles for CeF3 and well known BaF, crystals . It is clear that a heavier CcF3 crystal gives opportunity to change a calorimeter cell for a smaller one and thus improving the space and
two-shower resolution, which is important for the central zone of electromagnetic calorimeters. 4. Conclusion
The divalent dopants to CeF3 reduce the crystal light output, however the decay time falls down and radiation hardness increases . We have obtained decay constant of 28.3 ns and radiation hardness exceeding 108 rad for CcF; (0.67% Ba). So, CeF3(Ba) a fast and radiation hard scintillator appears to be quite promising for electromagnetic calorimetry in high energy physics . Acknowledgements The authors consider it necessary to express their thanks to A.A. Komar for his support of the work. Table 2 Decay constants and light output for doped CeF3 (for the slower component) Crystal composition
Decay constant [ns]
CeF3 (pure) CeF., (0.67% CeF, (1.16% CeF., (0.25°1c CeF, (1 .48% CeF, (0.12% CeF3 (0.60%
32.9±0.7 28.3+0.7 28.6±0.6 28.2±0.6 28.5±0.7 27.0 + v.5 27.6+0.6
Ba) Ba) Ca) Ca) Sr) Sr)
Relative light output [E1] 100 82.3 74.0 89.4 62.2 92.3 82.3
A .A . Aseet , et al f CeF j (a ) raci utiort horrd svintillatur
Trans mission, J7
CeF'3(pure) s
r
100 90 80 70 60
before irrit
50 40 30 t
M 8 t - 4td
i-Ifter
10 2,50
300
;:3 ;)0
400
1150
WaveIc-I1grt Il .
Transmis sion . [%] (b) 90
~60
600
1111111
C .eI+
inn
r,00
a
3(,Ba .) ._,. 0,677, '
80 70 60 50 40 30 20 10 o
r i
f
250
300
_-1 _-
350
400
450
Wavelength, [ n m ]
500
550
600
CeF3(Ca) 0 .25% 80 70
before irradiation
60 50
after 1 .2 x 10 7 rad
40
after 10 8 rad
:30 20 10
L---:250
300
350
400
4,50
Wavelength, [nrn]
500
550
600
Fig . 2 . Transmission spectra of CeF3 (pure) and CeF_3 + dopants before and after irradiation .
A.A . Aseer et al. / CeFYBa) radiation hard scintillatur
344 100
Transrnission,
90 80
70 60 50
before irradiation
40
after 1 .
30
x 10 7 ri-Ad
after 10 8 rad
20 10 0 250
i ,
.~.
350
300
_..__. .1
400
__
450
Wavelength, I'lam]
-._1
550
500
600
Fig. 2. (continued).
E=100 GeV
20 15 10 5 0
L ._____ _____ .__i___ .--__
0
1
2
R(CM)
3
4
5
Fig. 3 . Radial shower profiles of CeF.3 and BaF2 (GEANT3 Monte Carlo simulation).
eferences [11 D.F . Anderson, IEEE Trans. Nucl . Sci. NS-36 (1989) 137; D.F . Anderson, Nucl . Instr. and Meth . A287 (19 9, 0) 606. [21 W.W . Moses and S.E . Derenzo, IEEE Trans. Nucl . Sci. NS-36 (1989) 173 .
[31 [41 [51 [61
C.I . Britvich et al ., Preprint IHEP 90-154, Protvino, 1990 . M. Kobayashi et al ., KEK Preprint 90-130, 1990. M. Kobayashi et al ., KEK Preprint 90-140, 1990 . L.M . Bollinger and G.E . Thomas, Rev. Sci . Instr. 32 (1961) 1044.
NUCLEAR INSTRUMENTS &METHODS IN PHYSICS RESEARCH
Section A
a) radiation hard scintillator for electromagnetic calorimeters A.A. Aseev, E.G. Devitsin, V.A. Kozlov, Yu.I . Hovsepyan, S.Yu. Potashov, K.A. Sokolovsky and .V. Uvarova P.N. Lc bedev Physical Institute o f the Academy of Sciences of the USSR, Moscow, USSR V.G. Vasilchenko
Institute for Nigh Energi, Pltysicv, Prowino, USSR Received 28 August 1991
The influence of divalent fluoride dopants BaF.,, CaF 2 , SrF2 on radiation and luminescent properties of CeF; crystal is studied. A high radiation hardness ( > 10 8 rad) has been obtained for CeF., crystals doped with BaF, .
1. Introduction
In connection with new experimental tasks, which are to arise at future accelerators, the problem of creation of fast radiation hard crystals is emerging. It is a common knowledge that calorimeter elements must withstand dose rates of about 107 rad/yr and more. In addition, calorimeter radiator materials must have a short radiation length and a small Molière radius. In refs. [1-5] it is pointed out that a heavy inorganic scintillator CcF3 seems rather promising for applications in e.m. calorimetry of future accelerators due to its short decay time and huge light yield. Table 1 shows the main characteristics of CeF; (pure) [1]. Radiation hardness of CcF; (pure) has been alreadv investigated [3-5]. 2. Technique In current work the radiation and luminescent properties of CcF3 doped with BaF,, CaF,, SrF, up to 1.5% (by weight) are studied . The synthesis of CcF; monocrystals doped with Ca, Sr, Ba was performed with the help of specially prepared mixture for the growth in accordance with a technological scheme, consisting of sequentially following operations of multiple impregnation of the material by fluorine with the purpose of its full refinement from oxygen mixture . The crystal growth was carried out by the vertically directed crystallization technique (Bridge an-Stockbarger method) in the fluorine environment .
Decay times of CeF3 crystals were investigated using a delayed coincidence technique [5]. Samples of 1 cm in diameter and 5 mm thick, irradiated by "7Cs, were placed in a steel tube with two photomultipliers (PMT-71) with quartz windows on both sides. The samples were optically coupled to START PMT with a help of silicon grease (Rhodorsil) . The STOP PMT, situated at a distance of 10 cm from the crystal, operated in a photon counting mode. This setup is capable of measuring decal , times of up to 100 ns with 1 ns resolution . 3. Results For example some of the obtained scintillation decay curves are presented in figs. la-ld. The curves were fit by an exponential dependence in order to get decay constants. For the slower component the results are provided for different divalent fluoride dopants in table 2. Table, i The main characteristics of CeF; (pure) [1] Density [g/cm;] Radiation length [cm] Molière radius [cm] Decay constant [ns] Peak emission [nm] Index of refraction Light yield [%] (Nal(TI) = 100%) Hygroscopie
0168-91)02/92/$05 .00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
6.16 1 .7 2.72 5(short), 300ong) 310 (short), 340 (long) 1 .68 4-5 No
A.A . Aseev et al. / Cel"ffa) radiation hard scintillator 1()000
341
CeP3(f'ure)
Coil 11 Us
1:
'
S~-int
time '12 !) fr .-,
""ea e
e
e fes
ue
ee e e H, 'eNa " ,e
1()0
ee e
0
loooo
ee,e,e,e
20
40
60
e " e e e
80
Tinte Cris]
Counts
aa
1011
CeF3(Ba 0.67%)
M
Scint. time 28 3 ns
1000 ~
s
100 a
io l_ _-_ -_ 0
20
40
e
e
"aa
ee
e®
e
1000
e a
e
" ea
Scuit
time 28 2 ns
s ee
aa eee e e a
am,
s
100
100
CE , F:3((%3 0 .25-:1 '
e
--
80
Time [ns]
Counts e
- ______-_ I---
60
e
mo
ee ae ",
s ° ae s e e e a s
e
°
®
ee
m
e ee s ,w °"e e
e a , ms
101 0
1
20
-I
__-
40
L
-
60
Time [ns]
J_ 80
100
Fig . 1 . Scintillation decay curves of CeF3 (pure) and CeF; + dopants with quartz PMT at room temperature .
A.A . Astvt, et al. / CeF j%d radiation hard scintillator
342
()
Count-8
100001
,
~d)
h me 27 0 iv,
e
10
(i()
'l'it))o (lis l Fig. 1 . (continued) .
Only statistical errors are shown . It is clear that such a doping leads to a decrease in the decay constant from 32.9 ns for CcF; (pure) to 27.0 ns for CcF3 (0.12% Sr). The light output of CeF; doped with divalent fluorides was measured by comparing its response to 0.662 MeV photons ("'Cs) to that of a pure CeF3 crystal under the equal experimental environment . The CcFj (with dopants) samples of the same size were enveloped with a reflective Teflon tape and optically coupled to a quartz window PMT. For each sample under investigation there was obtained a photopeak corresponding to the 0.662 MeV photon in pulse height spectrum . The results are provided in table 2. It is clear that with such an amount of dopants light output falls down to 62.2% for CeF3 (1.48% Ca). There also have been performed some measurements of radiation hardness of CeF 3 (with dopants) crystals by exposing them to 1 .2 x 10 7 rad and 10 8 rad of -y-rays of 61) Co at the rate of 330 rad/s. The light transmission of crystals was measured before and after irradiation (figs. 2a-2d). A reduction in transmission of = 11% was obtained for CcF; (pure) in peak emission spectra (340 nm) after an exposed dose of 1.2 x 10 7 rad . Such a reduction for CeF,(Ca) and CeF3(Sr) reached = 5% for the same dose. There was no reduction in transmission spectra for CeF3 (Ba) after the dose of 1 .2 x 107 rad and small reduction for 10' rad . Fig . 3 illustrates simulated by the GEANT3 Monte Carlo program radial shower profiles for CeF3 and well known BaF, crystals . It is clear that a heavier CcF3 crystal gives opportunity to change a calorimeter cell for a smaller one and thus improving the space and
two-shower resolution, which is important for the central zone of electromagnetic calorimeters. 4. Conclusion
The divalent dopants to CeF3 reduce the crystal light output, however the decay time falls down and radiation hardness increases . We have obtained decay constant of 28.3 ns and radiation hardness exceeding 108 rad for CcF; (0.67% Ba). So, CeF3(Ba) a fast and radiation hard scintillator appears to be quite promising for electromagnetic calorimetry in high energy physics . Acknowledgements The authors consider it necessary to express their thanks to A.A. Komar for his support of the work. Table 2 Decay constants and light output for doped CeF3 (for the slower component) Crystal composition
Decay constant [ns]
CeF3 (pure) CeF., (0.67% CeF, (1.16% CeF., (0.25°1c CeF, (1 .48% CeF, (0.12% CeF3 (0.60%
32.9±0.7 28.3+0.7 28.6±0.6 28.2±0.6 28.5±0.7 27.0 + v.5 27.6+0.6
Ba) Ba) Ca) Ca) Sr) Sr)
Relative light output [E1] 100 82.3 74.0 89.4 62.2 92.3 82.3
A .A . Aseet , et al f CeF j (a ) raci utiort horrd svintillatur
Trans mission, J7
CeF'3(pure) s
r
100 90 80 70 60
before irrit
50 40 30 t
M 8 t - 4td
i-Ifter
10 2,50
300
;:3 ;)0
400
1150
WaveIc-I1grt Il .
Transmis sion . [%] (b) 90
~60
600
1111111
C .eI+
inn
r,00
a
3(,Ba .) ._,. 0,677, '
80 70 60 50 40 30 20 10 o
r i
f
250
300
_-1 _-
350
400
450
Wavelength, [ n m ]
500
550
600
CeF3(Ca) 0 .25% 80 70
before irradiation
60 50
after 1 .2 x 10 7 rad
40
after 10 8 rad
:30 20 10
L---:250
300
350
400
4,50
Wavelength, [nrn]
500
550
600
Fig . 2 . Transmission spectra of CeF3 (pure) and CeF_3 + dopants before and after irradiation .
A.A . Aseer et al. / CeFYBa) radiation hard scintillatur
344 100
Transrnission,
90 80
70 60 50
before irradiation
40
after 1 .
30
x 10 7 ri-Ad
after 10 8 rad
20 10 0 250
i ,
.~.
350
300
_..__. .1
400
__
450
Wavelength, I'lam]
-._1
550
500
600
Fig. 2. (continued).
E=100 GeV
20 15 10 5 0
L ._____ _____ .__i___ .--__
0
1
2
R(CM)
3
4
5
Fig. 3 . Radial shower profiles of CeF.3 and BaF2 (GEANT3 Monte Carlo simulation).
eferences [11 D.F . Anderson, IEEE Trans. Nucl . Sci. NS-36 (1989) 137; D.F . Anderson, Nucl . Instr. and Meth . A287 (19 9, 0) 606. [21 W.W . Moses and S.E . Derenzo, IEEE Trans. Nucl . Sci. NS-36 (1989) 173 .
[31 [41 [51 [61
C.I . Britvich et al ., Preprint IHEP 90-154, Protvino, 1990 . M. Kobayashi et al ., KEK Preprint 90-130, 1990. M. Kobayashi et al ., KEK Preprint 90-140, 1990 . L.M . Bollinger and G.E . Thomas, Rev. Sci . Instr. 32 (1961) 1044.