- Email: [email protected]
Radiation resistance of heavy scintillators to low-energy gamma-rays
ARTICLE IN PRESS
Radiation Physics and Chemistry 71 (2004) 705–707
Radiation resistance of heavy scintillators to low-energy gamma-rays Peter Kozmaa,*, Petr Kozma, Jr.b a b
Institute of Technological Investigations, 251 63 Strancˇice, Spojovac!ı 377, Czech Republic YXELL Ltd., Hi-Tech and Engineering, 251 63 Strancˇice, Spojovac!ı 377, Czech Republic
Abstract Radiation resistance of BGO, fluoride (BaF2, CeF3) and tungstate (PbWO4, CdWO4) heavy scintillation crystals due to low-energy gamma-rays has been studied for doses up to 105 Gy. Results are discussed in terms of degradation of transmission and appropriated induced absorption coefficients. The recovery time has been estimated from measurement of transmission spectra during 0.5–15 days after irradiations. r 2004 Elsevier Ltd. All rights reserved. Keywords: Scintillation crystals; Optical transmission; Radiation resistivity; Recovery time
High atomic number scintillation crystals, such as bismuth germanate (BGO), fluorides (BaF2, CeF3) and tungstates (PbWO4, CdWO4) are considered among the favourite scintillators in high-energy physics experiments (Lecoq, 1997). These crystals are also widely used in nuclear medicine diagnostic systems, particularly, positropn emission tomography (PET) and computerised tomography scanners (CTS) (Lu and ChengSheng, 1997). Because the radiation hardness of heavy scintillation detectors is known to be their most critical parameter, we are particularly interested in the investigation of radiation hardness of these crystals (Kozma et al., 1992, 1993, 1997, 1998, 2000, 2002a,b; Kozma and Kozma Jr., 2002, 2003; Kozma and Yanovsky, 2000) for absorption doses up to 105 Gy. In our experiments the radiation resistance of BGO, fluorides and tungstates was examined by measuring the optical transmission through them before and after 60Co gamma-ray irradiations (Kozma et al., 1993). The transmission spectra before and after absorption dose of 104 and 105 Gy are displayed in Fig. 1. The absolute degradation of transmission at the peak emission wavelength, per unit radiation length (Lecoq, 1977) is compared in Table 1. *Corresponding author. E-mail address: [email protected] (P. Kozma).
The induced absorption coefficients Dk, defined by Dk ¼ ð1=LÞlogðTbefore
irr =Tafter irr Þ;
ð1Þ
where L is the length of crystal, are also listed in Table 1. The recovery time of radiation damage has been estimated from measurement of transition spectra during 0.5–15 days after irradiations at 105 Gy. The experimental points at the peak emission wavelength have been least-square fitted by Tirr ðtÞ=Tð0Þ ¼ 1 expðbtÞ;
ð2Þ
where Tirr (t) is the transition measured at time t, T(0) the transition before irradiation and the fitting parameter b describes the recovery. The results are also listed in Table 1. The results obtained for gamma-rays irradiations are compared with those obtained for fast neutrons (14.7 MeV) irradiations (Kozma and Kozma Jr., 2004). The experimental results presented here can be summarized as follows: (a) Radiation damage of BGO, fluoride and tungstate scintillation crystals, at 104 Gy accumulated low energy gamma-ray dose, were found to be very similar. Radiation damage of these crystals is significant at 105 Gy accumulated dose: the absolute degradation of transmission is about 10%.
0969-806X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2004.04.063
ARTICLE IN PRESS P. Kozma, P. Kozma Jr. / Radiation Physics and Chemistry 71 (2004) 705–707
706
BGO
Ø 3.0 x 3.0 cm3
80
BaF2
TRANSMISSION [%]
60
3.0 x 3.0 x 12.5 cm3
40
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
20
CeF3
PbWO4
3.0 x 3.0 x 6.0 cm3
2.2 x 2.2 x 25.0 cm3
80 60 40
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
20 400
500
400
500
WAVELENGTH [nm] Fig. 1. Comparison of transmission spectra before and after 60Co gamma-ray irradiations for BGO, PbWO4, BaF2 and CeF3 scintillation crystals. The optical transmissions were measured longitudinally.
Table 1 Absolute degradation of transmission, induced absorption coefficients (Dk) and recovery time coefficients (b) for scintillation crystals at peak emission wavelength Scintillation Peak emission Gamma-rays irradiations crystal wavelength (nm) Degradation (%) Dk (m1)
BGO BaF2 CeF3 PbWO4 CdWO4
480 325 300 420 470
Fast neutron irradiations
104 Gy
105 Gy
104 Gy 105 Gy
3.4 6.7 2.8 7.5 4.8
7.5 12.0 10.1 12.5 8.0
0.62 0.49 0.44 0.48 0.21
(b) Induced absorption coefficients substantially increase for a 105 Gy accumulated dose. (c) Radiation damage due to low-energy gamma-rays is recovered on only a few days.
References Kozma, P., Kozma Jr. P., 2002. Radiation resistivity of small BGO crystals. In: Proceedings of the International Nuclear Conference INC’02, Kuala Lumpur, October 15–18, 2002, Malaysian Nuclear Society Press, 177.
1.24 0.90 0.79 0.85 0.39
Recovery time b Degradation Dk (m1) after 105 Gy 105 Gy 105 Gy (day1)
Recovery time b after 105 Gy (day1)
2:670:4 1:270:2 1:370:2 3:670:6 3:370:5
14:571:2 10:171:0 9:571:0 15:571:4 15:071:3
4.1 7.7 3.6 9.5 5.3
1.75 1.34 1.22 1.10 1.05
Kozma, P., Kozma Jr., P., 2003. Radiation resistivity of BGO crystals due to low-energy gamma-rays. Nucl. Instrum. Methods A 501, 499–504. Kozma, P., Kozma, Jr. P., 2004. Nucl. Instrum. Methods, accepted for publication. Kozma, P., Afanasiev, S., Malakhov, A., Povtoreiko, A., 1992. A cerium fluoride scintillator working with FEU-140. Nucl. Instrum. Methods A 322, 302–308. Kozma, P., Afanasiev, S., Malakhov, A., Povtoreiko, A., 1993. Radiation resistivity of large CeF3 crystals. Nucl. Instrum. Methods A 328, 599–600. Kozma, P., Bajgar, R., Kozma Jr. P., 1997. Radiation resistivity of PbWO4 crystals. In: Zhiwen, Yin, et al.
ARTICLE IN PRESS P. Kozma, P. Kozma Jr. / Radiation Physics and Chemistry 71 (2004) 705–707 (Eds.), Proceedings of the International Conference SCINT’97, Shanghai, People’s Republic of China, September 22–26, 1997, CAS Shanghai Brand Press, p. 248. Kozma, P., Bajgar, R., Kozma Jr. P., 1998. Radiation resistivity of tungstate crystals. In: Baccaro, S., et al. (Eds.), Proceedings of the International Workshop on Tungstate Crystals, Roma, October 12–14, University La Sapienza Press, p. 199. Kozma, P., Bajgar, R., Kozma Jr., P., 2000. Radiation resistivity of large tungstate crystals. Radiat. Phys. Chem. 59, 377–380. Kozma, P., Bajgar, R., Kozma Jr., P., 2002. Radiation resistivity of PbF2 crystals. Nucl. Instrum. Methods A 484, 149–152. Kozma, P., Bajgar, R., Kozma Jr., P., 2002. Radiation damage of PbWO4 crystals due to radiation by 60Co gamma-rays. Radiat. Phys. Chem. 65, 127–130.
707
Kozma, P., Yanovsky, V.V., 2000. Application of BaF2 scintillator to off-line spectroscopy. Czech. J. Phys. B 40, 393–397. Lecoq, P., 1997. The challenge of new scintillation development for high energy physics. In: Yin, Z.-W. et al. (Eds.), Proceedings of the International Conference SCINT’97, Shanghai, People’s Republic of China, September 22–26, 1997, CAS Shanghai Brand Press, p. 22. Lu, Z.M., Cheng-Sheng, T.X., 1997. Application of scintillation crystals in nuclear medicine. In: Yin, Z.-W. et al. (Eds.), Proceedings of the International Conference SCINT’97, Shanghai, People’s Republic of China, September 22–26, 1997, CAS Shanghai Brand Press, 18.
Radiation Physics and Chemistry 71 (2004) 705–707
Radiation resistance of heavy scintillators to low-energy gamma-rays Peter Kozmaa,*, Petr Kozma, Jr.b a b
Institute of Technological Investigations, 251 63 Strancˇice, Spojovac!ı 377, Czech Republic YXELL Ltd., Hi-Tech and Engineering, 251 63 Strancˇice, Spojovac!ı 377, Czech Republic
Abstract Radiation resistance of BGO, fluoride (BaF2, CeF3) and tungstate (PbWO4, CdWO4) heavy scintillation crystals due to low-energy gamma-rays has been studied for doses up to 105 Gy. Results are discussed in terms of degradation of transmission and appropriated induced absorption coefficients. The recovery time has been estimated from measurement of transmission spectra during 0.5–15 days after irradiations. r 2004 Elsevier Ltd. All rights reserved. Keywords: Scintillation crystals; Optical transmission; Radiation resistivity; Recovery time
High atomic number scintillation crystals, such as bismuth germanate (BGO), fluorides (BaF2, CeF3) and tungstates (PbWO4, CdWO4) are considered among the favourite scintillators in high-energy physics experiments (Lecoq, 1997). These crystals are also widely used in nuclear medicine diagnostic systems, particularly, positropn emission tomography (PET) and computerised tomography scanners (CTS) (Lu and ChengSheng, 1997). Because the radiation hardness of heavy scintillation detectors is known to be their most critical parameter, we are particularly interested in the investigation of radiation hardness of these crystals (Kozma et al., 1992, 1993, 1997, 1998, 2000, 2002a,b; Kozma and Kozma Jr., 2002, 2003; Kozma and Yanovsky, 2000) for absorption doses up to 105 Gy. In our experiments the radiation resistance of BGO, fluorides and tungstates was examined by measuring the optical transmission through them before and after 60Co gamma-ray irradiations (Kozma et al., 1993). The transmission spectra before and after absorption dose of 104 and 105 Gy are displayed in Fig. 1. The absolute degradation of transmission at the peak emission wavelength, per unit radiation length (Lecoq, 1977) is compared in Table 1. *Corresponding author. E-mail address: [email protected] (P. Kozma).
The induced absorption coefficients Dk, defined by Dk ¼ ð1=LÞlogðTbefore
irr =Tafter irr Þ;
ð1Þ
where L is the length of crystal, are also listed in Table 1. The recovery time of radiation damage has been estimated from measurement of transition spectra during 0.5–15 days after irradiations at 105 Gy. The experimental points at the peak emission wavelength have been least-square fitted by Tirr ðtÞ=Tð0Þ ¼ 1 expðbtÞ;
ð2Þ
where Tirr (t) is the transition measured at time t, T(0) the transition before irradiation and the fitting parameter b describes the recovery. The results are also listed in Table 1. The results obtained for gamma-rays irradiations are compared with those obtained for fast neutrons (14.7 MeV) irradiations (Kozma and Kozma Jr., 2004). The experimental results presented here can be summarized as follows: (a) Radiation damage of BGO, fluoride and tungstate scintillation crystals, at 104 Gy accumulated low energy gamma-ray dose, were found to be very similar. Radiation damage of these crystals is significant at 105 Gy accumulated dose: the absolute degradation of transmission is about 10%.
0969-806X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2004.04.063
ARTICLE IN PRESS P. Kozma, P. Kozma Jr. / Radiation Physics and Chemistry 71 (2004) 705–707
706
BGO
Ø 3.0 x 3.0 cm3
80
BaF2
TRANSMISSION [%]
60
3.0 x 3.0 x 12.5 cm3
40
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
20
CeF3
PbWO4
3.0 x 3.0 x 6.0 cm3
2.2 x 2.2 x 25.0 cm3
80 60 40
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
before irradiation 1.0 x 104 Gy 1.0 x 105 Gy
20 400
500
400
500
WAVELENGTH [nm] Fig. 1. Comparison of transmission spectra before and after 60Co gamma-ray irradiations for BGO, PbWO4, BaF2 and CeF3 scintillation crystals. The optical transmissions were measured longitudinally.
Table 1 Absolute degradation of transmission, induced absorption coefficients (Dk) and recovery time coefficients (b) for scintillation crystals at peak emission wavelength Scintillation Peak emission Gamma-rays irradiations crystal wavelength (nm) Degradation (%) Dk (m1)
BGO BaF2 CeF3 PbWO4 CdWO4
480 325 300 420 470
Fast neutron irradiations
104 Gy
105 Gy
104 Gy 105 Gy
3.4 6.7 2.8 7.5 4.8
7.5 12.0 10.1 12.5 8.0
0.62 0.49 0.44 0.48 0.21
(b) Induced absorption coefficients substantially increase for a 105 Gy accumulated dose. (c) Radiation damage due to low-energy gamma-rays is recovered on only a few days.
References Kozma, P., Kozma Jr. P., 2002. Radiation resistivity of small BGO crystals. In: Proceedings of the International Nuclear Conference INC’02, Kuala Lumpur, October 15–18, 2002, Malaysian Nuclear Society Press, 177.
1.24 0.90 0.79 0.85 0.39
Recovery time b Degradation Dk (m1) after 105 Gy 105 Gy 105 Gy (day1)
Recovery time b after 105 Gy (day1)
2:670:4 1:270:2 1:370:2 3:670:6 3:370:5
14:571:2 10:171:0 9:571:0 15:571:4 15:071:3
4.1 7.7 3.6 9.5 5.3
1.75 1.34 1.22 1.10 1.05
Kozma, P., Kozma Jr., P., 2003. Radiation resistivity of BGO crystals due to low-energy gamma-rays. Nucl. Instrum. Methods A 501, 499–504. Kozma, P., Kozma, Jr. P., 2004. Nucl. Instrum. Methods, accepted for publication. Kozma, P., Afanasiev, S., Malakhov, A., Povtoreiko, A., 1992. A cerium fluoride scintillator working with FEU-140. Nucl. Instrum. Methods A 322, 302–308. Kozma, P., Afanasiev, S., Malakhov, A., Povtoreiko, A., 1993. Radiation resistivity of large CeF3 crystals. Nucl. Instrum. Methods A 328, 599–600. Kozma, P., Bajgar, R., Kozma Jr. P., 1997. Radiation resistivity of PbWO4 crystals. In: Zhiwen, Yin, et al.
ARTICLE IN PRESS P. Kozma, P. Kozma Jr. / Radiation Physics and Chemistry 71 (2004) 705–707 (Eds.), Proceedings of the International Conference SCINT’97, Shanghai, People’s Republic of China, September 22–26, 1997, CAS Shanghai Brand Press, p. 248. Kozma, P., Bajgar, R., Kozma Jr. P., 1998. Radiation resistivity of tungstate crystals. In: Baccaro, S., et al. (Eds.), Proceedings of the International Workshop on Tungstate Crystals, Roma, October 12–14, University La Sapienza Press, p. 199. Kozma, P., Bajgar, R., Kozma Jr., P., 2000. Radiation resistivity of large tungstate crystals. Radiat. Phys. Chem. 59, 377–380. Kozma, P., Bajgar, R., Kozma Jr., P., 2002. Radiation resistivity of PbF2 crystals. Nucl. Instrum. Methods A 484, 149–152. Kozma, P., Bajgar, R., Kozma Jr., P., 2002. Radiation damage of PbWO4 crystals due to radiation by 60Co gamma-rays. Radiat. Phys. Chem. 65, 127–130.
707
Kozma, P., Yanovsky, V.V., 2000. Application of BaF2 scintillator to off-line spectroscopy. Czech. J. Phys. B 40, 393–397. Lecoq, P., 1997. The challenge of new scintillation development for high energy physics. In: Yin, Z.-W. et al. (Eds.), Proceedings of the International Conference SCINT’97, Shanghai, People’s Republic of China, September 22–26, 1997, CAS Shanghai Brand Press, p. 22. Lu, Z.M., Cheng-Sheng, T.X., 1997. Application of scintillation crystals in nuclear medicine. In: Yin, Z.-W. et al. (Eds.), Proceedings of the International Conference SCINT’97, Shanghai, People’s Republic of China, September 22–26, 1997, CAS Shanghai Brand Press, 18.