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Light yield dependence of a plastic scintillator excited with UV laser and radioactive source on radiation dose
Nuclear Instrumenrs and Methods in Physics Research A 381 (1996) 573-575
NUCLEAR INSTRUMENTS & METHODS IN PH SICS RESE x RCH Sectton A
Letter to the Editor
yield dependence of a plastic scintillator excited with UV laser and radioactive source on radiation dose VI. Kryshkin,
L.K. Turchanovich,
Institute for High Energy Physics, Received
9 January
016%9002/96/$15.00 Copyright PII SO168-9002(96)00743-7
142284 Protvino, Moscow Region, Russia
1996; revised form received
To monitor the performance of scintillator calorimeters, radioactive sources or light pulses (lasers or diodes emitting light in the visible wavelength region, see, for example, Ref. [ 11) are commonly used. Radioactive source calibration allows one to measure the light attenuation length of a scintillator and its uniformity, and to use an absolute calibration scale obtained in a test beam as a reference when transporting the calorimeter to the experimental setup. Besides, this method can be used for quality control at the assembly stage. The disadvantages of it are the following: - complicated mechanics is needed to move a radioactive source along each scintillator; _ the measurement is time consuming; - photodetectors must have an additional DC current output; -linearity, dynamical range, timing of the system (photodetectors, amplifiers, ADC) and determination of the photoelectron yield cannot be checked. With the light pulses one can monitor the entire chain starting from the photodetectors. With respect to the radiation hardness of plastic scintillators, the decrease of the light yield and transparency from their initial values are the main parameters which are to be checked. If scintillator light yield were unambiguously connected to scintillator radiation damage, the usefulness of UV light monitors would be greatly enhanced. We measured the scintillator light yield against the radiation damage when exciting the scintillator with a radioactive source and UV light. The scintillator, based on polystyrene doped with 1.5% pTP (paraterphenyl) and 0.05% POPOP (1,4-bis(2-(5-phenyloxazolyl))-benzene), had the following dimensions: 140 X 28 X 4mm. The narrow side of the scintillator was coupled to the photocathode of a FEU-84, a black paper was glued to the opposite side. The samples were irradiated in a flux of y-quanta from ‘37Cs radioactive sources with a dose rate of 6 rad/s (or 190 Mrad/yr) in room temperature air. * Corresponding author.
YG. Vasil’chenko” 14 May 1996
The layout of the measurements is presented in Fig. 1. The scintillator was exited by a nitrogen laser (A,,, = 337 nm) with 5 ns duration at 10 Hz frequency and by a radioactive source, “Sr. In the first case, the phototube pulse height was measured with a 3% precision with an ADC with a 90 ns length gate. When the scintillator was irradiated by ?G, the DC current was measured with 2% precision. The dependence of the phototube signal on the distance between the photocathode and the source is shown in Fig. 2 for different irradiation doses. The measurements are normalized at X = 53 mm for the scintillator before irradiation. The dependence of the phototube signal on the dose for X = 128 mm is presented in Fig. 3. The recovery of the scintillator light yield after irradiation is shown in Fig. 4. Within the errors both methods have yielded the same results. Thus if each scintillator in the calorimeter tower is illuminated in turn by UV light the following conclusions can be drawn: _ if the pulse height from a single scintillator drops then something has gone wrong with the light collection from the scintillator;
Fig. 1. The layout of measurements: 1 is the scintillator; 2 is the phototube FEU-84-3; 3 is the nitrogen laser LG-15U; 4 is the neutral filter; 5 is the quartz fibre; 6 is the optical connector; 7 is the radioactive source ?Sr; 8 is the ADC; 9 is the data acquisition system; 10 is the personal computer; I1 is the digital voltmeter.
0 1996 Elsevier Science B.V. All rights reserved
574
V.I. Kryshkin et al. I Nucl. Instr. and Meth. in P&s. Res. A 381 (1994) 573-575
0.4
-
0.2
-
0
-
-0.2
-
-0.4
-
I
0
20
40
60
80
100
120
140
X, mm Fig. 2. The scintillator light yield dependence on the distance between the photocathode and the source (the laser or the radioactive without irradiation and for 1OOkrad absorbed dose (lines were drawn by hand to guide the eye).
_ if the pulse height from all scintillators drops proportionally then the most probable reason lies in the photodetector, high voltage supply, or ADC; - if the pulse height from several scintillators, say, in
source)
the shower maximum, drops, the scintillators have been radiation damaged. Thus the UV laser can monitor all radiation sensitive elements of scintillator calorimeter. It is well-known [2]
x
-laser
0.8
-
0.6
5 d 0 X
0.4
IO4 dose, Fig. 3. The ratio of the light yield before and after irradiation
as a function
105
1 o6
rod
of the total dose (curve was drown by hand to guide the eye).
V.I. Kryshkin
et al. / Nucl. Instr. md Meth. in Phys. Res. A 381 (1996) 573-575
575
0.6
I
1
10
.
.
.
.,-
.,
'103
102
,
,
.
,
.,.,I
.
,
,
.,
,..,
,
.
.
104
hours Fig. 4. The recovery of the scintillator light yield vs time after 450 krad irradiation (solid line) and 1 Mrad irradiation (dotted line) (curves were drawn by hand to guide the eye). that the scintillator light yield excited by UV light does not depend on magnetic field in contrast to that excited with a radioactive source, which is an additional advantage for the UV light monitoring.
References [I] M. Bonesini et al., Preprint CERNEP/87-227, (1987);
Geneva
L. Antoniazi et al., Preprint FERMILAB-Pub-931001, Batavia (1993); A. Andresen et al., Preprint DESY 91-026, Hamburg (1991); H.H. Nguyen et al., Preprint FERMILAB-Conf-94/398, Batavia (1994); A.C. Dodd et al., Nucl. Instr. and Meth. A 336 (1993) 136. [2] D. Blomker et al., Preprint DESY 91-083, Hamburg (i991).
NUCLEAR INSTRUMENTS & METHODS IN PH SICS RESE x RCH Sectton A
Letter to the Editor
yield dependence of a plastic scintillator excited with UV laser and radioactive source on radiation dose VI. Kryshkin,
L.K. Turchanovich,
Institute for High Energy Physics, Received
9 January
016%9002/96/$15.00 Copyright PII SO168-9002(96)00743-7
142284 Protvino, Moscow Region, Russia
1996; revised form received
To monitor the performance of scintillator calorimeters, radioactive sources or light pulses (lasers or diodes emitting light in the visible wavelength region, see, for example, Ref. [ 11) are commonly used. Radioactive source calibration allows one to measure the light attenuation length of a scintillator and its uniformity, and to use an absolute calibration scale obtained in a test beam as a reference when transporting the calorimeter to the experimental setup. Besides, this method can be used for quality control at the assembly stage. The disadvantages of it are the following: - complicated mechanics is needed to move a radioactive source along each scintillator; _ the measurement is time consuming; - photodetectors must have an additional DC current output; -linearity, dynamical range, timing of the system (photodetectors, amplifiers, ADC) and determination of the photoelectron yield cannot be checked. With the light pulses one can monitor the entire chain starting from the photodetectors. With respect to the radiation hardness of plastic scintillators, the decrease of the light yield and transparency from their initial values are the main parameters which are to be checked. If scintillator light yield were unambiguously connected to scintillator radiation damage, the usefulness of UV light monitors would be greatly enhanced. We measured the scintillator light yield against the radiation damage when exciting the scintillator with a radioactive source and UV light. The scintillator, based on polystyrene doped with 1.5% pTP (paraterphenyl) and 0.05% POPOP (1,4-bis(2-(5-phenyloxazolyl))-benzene), had the following dimensions: 140 X 28 X 4mm. The narrow side of the scintillator was coupled to the photocathode of a FEU-84, a black paper was glued to the opposite side. The samples were irradiated in a flux of y-quanta from ‘37Cs radioactive sources with a dose rate of 6 rad/s (or 190 Mrad/yr) in room temperature air. * Corresponding author.
YG. Vasil’chenko” 14 May 1996
The layout of the measurements is presented in Fig. 1. The scintillator was exited by a nitrogen laser (A,,, = 337 nm) with 5 ns duration at 10 Hz frequency and by a radioactive source, “Sr. In the first case, the phototube pulse height was measured with a 3% precision with an ADC with a 90 ns length gate. When the scintillator was irradiated by ?G, the DC current was measured with 2% precision. The dependence of the phototube signal on the distance between the photocathode and the source is shown in Fig. 2 for different irradiation doses. The measurements are normalized at X = 53 mm for the scintillator before irradiation. The dependence of the phototube signal on the dose for X = 128 mm is presented in Fig. 3. The recovery of the scintillator light yield after irradiation is shown in Fig. 4. Within the errors both methods have yielded the same results. Thus if each scintillator in the calorimeter tower is illuminated in turn by UV light the following conclusions can be drawn: _ if the pulse height from a single scintillator drops then something has gone wrong with the light collection from the scintillator;
Fig. 1. The layout of measurements: 1 is the scintillator; 2 is the phototube FEU-84-3; 3 is the nitrogen laser LG-15U; 4 is the neutral filter; 5 is the quartz fibre; 6 is the optical connector; 7 is the radioactive source ?Sr; 8 is the ADC; 9 is the data acquisition system; 10 is the personal computer; I1 is the digital voltmeter.
0 1996 Elsevier Science B.V. All rights reserved
574
V.I. Kryshkin et al. I Nucl. Instr. and Meth. in P&s. Res. A 381 (1994) 573-575
0.4
-
0.2
-
0
-
-0.2
-
-0.4
-
I
0
20
40
60
80
100
120
140
X, mm Fig. 2. The scintillator light yield dependence on the distance between the photocathode and the source (the laser or the radioactive without irradiation and for 1OOkrad absorbed dose (lines were drawn by hand to guide the eye).
_ if the pulse height from all scintillators drops proportionally then the most probable reason lies in the photodetector, high voltage supply, or ADC; - if the pulse height from several scintillators, say, in
source)
the shower maximum, drops, the scintillators have been radiation damaged. Thus the UV laser can monitor all radiation sensitive elements of scintillator calorimeter. It is well-known [2]
x
-laser
0.8
-
0.6
5 d 0 X
0.4
IO4 dose, Fig. 3. The ratio of the light yield before and after irradiation
as a function
105
1 o6
rod
of the total dose (curve was drown by hand to guide the eye).
V.I. Kryshkin
et al. / Nucl. Instr. md Meth. in Phys. Res. A 381 (1996) 573-575
575
0.6
I
1
10
.
.
.
.,-
.,
'103
102
,
,
.
,
.,.,I
.
,
,
.,
,..,
,
.
.
104
hours Fig. 4. The recovery of the scintillator light yield vs time after 450 krad irradiation (solid line) and 1 Mrad irradiation (dotted line) (curves were drawn by hand to guide the eye). that the scintillator light yield excited by UV light does not depend on magnetic field in contrast to that excited with a radioactive source, which is an additional advantage for the UV light monitoring.
References [I] M. Bonesini et al., Preprint CERNEP/87-227, (1987);
Geneva
L. Antoniazi et al., Preprint FERMILAB-Pub-931001, Batavia (1993); A. Andresen et al., Preprint DESY 91-026, Hamburg (1991); H.H. Nguyen et al., Preprint FERMILAB-Conf-94/398, Batavia (1994); A.C. Dodd et al., Nucl. Instr. and Meth. A 336 (1993) 136. [2] D. Blomker et al., Preprint DESY 91-083, Hamburg (i991).