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Radiation resistivity of large tungstate crystals
Radiation Physics and Chemistry 59 (2000) 377±380
www.elsevier.com/locate/radphyschem
Technical note
Radiation resistivity of large tungstate crystals Peter Kozma a,*, Robert Bajgar b, Petr Kozma a Jr. a
Institute of Technological Investigations, 251 63 StrancÏice, Prague Eastern District, Czech Republic Oregon Graduate Institute of Science and Technology, P.O. Box 91000, Portland, OR 97291-1000, USA
b
Received 4 June 1999; accepted 13 March 2000
Abstract Radiation resistivity of large tungstate crystals PbWO4 and CdWO4 has been studied for doses up to 105 Gy. Radiation resistivity was examined by the measurement of optical transmission through tungstate crystals before and after gamma-ray irradiations. The absolute degradation of transmission for 105 Gy dose at the wavelength of the peak emission of both tungstate crystals PbWO4 and CdWO4 were found to be lower than 12.5 and 8.0%, respectively. The complete recovery of radiation damage was observed 15 days after irradiations. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Scintillation crystals; Tungstate crystals; Lead tungstate; Cadmium tungstate; Radiation resistivity; Gamma-ray irradiations; Optical transmission; CT scanners; Electromagnetic calorimeters
1. Introduction PbWO4 crystal is considered among the most promising scintillators, particularly, because of its high density (8.3 g/cm3), short radiation length and small Moliere radius. Because of these properties, crystalline PbWO4 seems to be the most promising scintillator for use in the LHC project at CERN (Lecoq, 1997). CdWO4 crystals are considered among the most promising scintillators for application in nuclear medicine, particularly in CT scanners, because of their high density (7.9 g/cm3) and relatively large light yield (Zusheng et al., 1997). The basic properties of tungstate crystals are listed in Table 1. The radiation hardness of tungstate crystals
* Corresponding author. Tel.: +42-204-640176; fax: +42204-640438. E-mail address: [email protected] (P. Kozma).
PbWO4and CdWO4 is known to be the crucial parameter, and therefore, we continue to investigate radiation hardness of these crystals. In this work, we report on the radiation hardness of 2:2 2:2 25 cm3 PbWO4 and 2:0 2:0 19:5 cm3 CdWO4 crystals at accumulated doses of low energy gamma-rays up to 105 Gy. The results are compared with those published earlier (Kozma et al., 1997) for a 2:2 2:2 11:2 cm3 crystal of PbWO4. 2. Experimental results PbWO4 and CdWO4 crystals were irradiated by a Co gamma-ray source. The radiation resistivity was examined by the measurement of transmission spectra before and after irradiation. Irradiation conditions and optical transmission spectra measurements were identical to those described in Kozma et al., (1993). The changes of transmission of PbWO4and CdWO4 crystals 60
0969-806X/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 0 ) 0 0 2 9 6 - 6
378
P. Kozma et al. / Radiation Physics and Chemistry 59 (2000) 377±380
Fig. 1. Transmission spectra before and after
after absorption of 104 and 105 Gy accumulated doses are displayed in Figs. 1 and 2, respectively. The corresponding variation of absorption coecients Dk, de®ned by Tirrad =Tinit exp ÿDkL, is displayed in Fig. 3. The comparison of transmission for PbWO4, CdWO4 and CeF3 (Kozma et al., 1993) large volume crystals for doses 104 and 105 Gy at the peak emission wavelength (480, 470 and 375 nm, respectively) are listed in Table 2. The absolute degradation of transmission of all these crystals is compared in Table 3.
60
Co gamma-ray irradiation.
3. Conclusions It can be seen that the present data for PbWO4 crystal of dimensions 2:2 2:2 25 cm3 (sample #2) are substantially better than those published earlier for 2:2 2:2 11:2 cm3 lead tungstate crystal sample (sample #1) (Kozma et al., 1997): the degradation of transmission at peak emission was found to be lower than 7.5 and 12.5% for doses 104 and 105 Gy gammarays, respectively. The sucient improvement of lead
Fig. 2. Transmission spectra before and after
60
Co gamma-ray irradiation.
P. Kozma et al. / Radiation Physics and Chemistry 59 (2000) 377±380 Table 1 Properties of tungstate crystals Crystal
PbWO4
CdWO4
Density (g/cm3) Melting point (8C) Radiation length (cm) Moliere radius (cm) Refractive index a Hygroscopicity Wavelength (nm) Decay time b(ms) Light yield c (%)
8.3 1123 0.9 2.0 2.2 None 480 50/10 30±40
7.9 1325 1.1 2.2 2.3 None 470 20/5 25±30
a
At the wavelength of the maximum. Slow/fast component. c Relative to NaI(Tl) for gamma-rays.
b
379
tungstate crystal radiation hardness until the level required for application in electromagnetic calorimeters of the CERN LHC experiments has been achieved particularly by additional doping of crystals and re®ned puri®cation of raw materials PbO and WO3, as well. It can be also seen that CdWO4 crystal of large volume has a very good radiation resistance: for doses of 104 and 105 Gy gamma-rays, the optical transmission of the irradiated crystal decreases by less than 4.8 and 8.0%, respectively. These values are comparable with those published earlier (Kozma et al., 1993) for CeF3 scintillation crystal of large volume. The measurement of transmission 15 days after 105 Gy irradiations showed the complete recovery of both examined tungstate crystals.
Fig. 3. Comparison of absorption coecients.
380
P. Kozma et al. / Radiation Physics and Chemistry 59 (2000) 377±380
Table 2 Transmission at peak emission Dose (Gy)
PbWO4 #1 (480 nm), %
PbWO4 #2 (480 nm), %
CdWO4 (470 nm), %
CeF3 (375 nm), %
0 104 105
70.0 59.5 50.5
72.0 67.0 63.5
77.5 74.5 71.5
82.8 80.0 74.5
Table 3 Degradation of transmission at peak emission Dose (Gy)
PbWO4 #1 (480 nm), %
PbWO4 #2 (480 nm), %
CdWO4 (470 nm), %
CeF3 (375 nm), %
104 105
15.0 27.5
7.5 12.5
4.8 8.0
2.8 10.0
References Kozma, P., Bajgar, R., Kozma Jr., P., 1997. Radiation resistivity of PbWO4 crystals. In: Zhiwen, Yin, et al. (Eds.), Proc. of the Int. Conf. SCINT'97, Shanghai, People's Republic of China, Sept. 22±26. CAS Shanghai Branch Press, p. 248. Kozma, P., Afanasiev, S., Malakhov, A., Povtoreiko, A., 1993. A cerium ¯uoride scintillator coupled to a FEU-140 photomultiplier. Nucl. Instr. and Meth. A328, 599±600.
Lecoq, P., 1997. The challenge of new scintillator development for high energy physics. In: Zhiwen, Yin, et al. (Eds.), Proc. of the Int. Conf. SCINT'97, Shanghai, People's Republic of China, Sept. 22±26. CAS Shanghai Branch Press, p. 13. Lu, Zusheng, Mao, Chengsheng, Tang, Xiaowei, 1997. Application of scintillation crystals in nuclear medicine. In: Zhiwen, Yin, et al. (Eds.), Proc. of the Conf. SCINT'97, Shanghai, People's Republic of China, Sept. 22±26. CAS Shanghai Branch Press, p. 18.
www.elsevier.com/locate/radphyschem
Technical note
Radiation resistivity of large tungstate crystals Peter Kozma a,*, Robert Bajgar b, Petr Kozma a Jr. a
Institute of Technological Investigations, 251 63 StrancÏice, Prague Eastern District, Czech Republic Oregon Graduate Institute of Science and Technology, P.O. Box 91000, Portland, OR 97291-1000, USA
b
Received 4 June 1999; accepted 13 March 2000
Abstract Radiation resistivity of large tungstate crystals PbWO4 and CdWO4 has been studied for doses up to 105 Gy. Radiation resistivity was examined by the measurement of optical transmission through tungstate crystals before and after gamma-ray irradiations. The absolute degradation of transmission for 105 Gy dose at the wavelength of the peak emission of both tungstate crystals PbWO4 and CdWO4 were found to be lower than 12.5 and 8.0%, respectively. The complete recovery of radiation damage was observed 15 days after irradiations. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Scintillation crystals; Tungstate crystals; Lead tungstate; Cadmium tungstate; Radiation resistivity; Gamma-ray irradiations; Optical transmission; CT scanners; Electromagnetic calorimeters
1. Introduction PbWO4 crystal is considered among the most promising scintillators, particularly, because of its high density (8.3 g/cm3), short radiation length and small Moliere radius. Because of these properties, crystalline PbWO4 seems to be the most promising scintillator for use in the LHC project at CERN (Lecoq, 1997). CdWO4 crystals are considered among the most promising scintillators for application in nuclear medicine, particularly in CT scanners, because of their high density (7.9 g/cm3) and relatively large light yield (Zusheng et al., 1997). The basic properties of tungstate crystals are listed in Table 1. The radiation hardness of tungstate crystals
* Corresponding author. Tel.: +42-204-640176; fax: +42204-640438. E-mail address: [email protected] (P. Kozma).
PbWO4and CdWO4 is known to be the crucial parameter, and therefore, we continue to investigate radiation hardness of these crystals. In this work, we report on the radiation hardness of 2:2 2:2 25 cm3 PbWO4 and 2:0 2:0 19:5 cm3 CdWO4 crystals at accumulated doses of low energy gamma-rays up to 105 Gy. The results are compared with those published earlier (Kozma et al., 1997) for a 2:2 2:2 11:2 cm3 crystal of PbWO4. 2. Experimental results PbWO4 and CdWO4 crystals were irradiated by a Co gamma-ray source. The radiation resistivity was examined by the measurement of transmission spectra before and after irradiation. Irradiation conditions and optical transmission spectra measurements were identical to those described in Kozma et al., (1993). The changes of transmission of PbWO4and CdWO4 crystals 60
0969-806X/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 0 ) 0 0 2 9 6 - 6
378
P. Kozma et al. / Radiation Physics and Chemistry 59 (2000) 377±380
Fig. 1. Transmission spectra before and after
after absorption of 104 and 105 Gy accumulated doses are displayed in Figs. 1 and 2, respectively. The corresponding variation of absorption coecients Dk, de®ned by Tirrad =Tinit exp ÿDkL, is displayed in Fig. 3. The comparison of transmission for PbWO4, CdWO4 and CeF3 (Kozma et al., 1993) large volume crystals for doses 104 and 105 Gy at the peak emission wavelength (480, 470 and 375 nm, respectively) are listed in Table 2. The absolute degradation of transmission of all these crystals is compared in Table 3.
60
Co gamma-ray irradiation.
3. Conclusions It can be seen that the present data for PbWO4 crystal of dimensions 2:2 2:2 25 cm3 (sample #2) are substantially better than those published earlier for 2:2 2:2 11:2 cm3 lead tungstate crystal sample (sample #1) (Kozma et al., 1997): the degradation of transmission at peak emission was found to be lower than 7.5 and 12.5% for doses 104 and 105 Gy gammarays, respectively. The sucient improvement of lead
Fig. 2. Transmission spectra before and after
60
Co gamma-ray irradiation.
P. Kozma et al. / Radiation Physics and Chemistry 59 (2000) 377±380 Table 1 Properties of tungstate crystals Crystal
PbWO4
CdWO4
Density (g/cm3) Melting point (8C) Radiation length (cm) Moliere radius (cm) Refractive index a Hygroscopicity Wavelength (nm) Decay time b(ms) Light yield c (%)
8.3 1123 0.9 2.0 2.2 None 480 50/10 30±40
7.9 1325 1.1 2.2 2.3 None 470 20/5 25±30
a
At the wavelength of the maximum. Slow/fast component. c Relative to NaI(Tl) for gamma-rays.
b
379
tungstate crystal radiation hardness until the level required for application in electromagnetic calorimeters of the CERN LHC experiments has been achieved particularly by additional doping of crystals and re®ned puri®cation of raw materials PbO and WO3, as well. It can be also seen that CdWO4 crystal of large volume has a very good radiation resistance: for doses of 104 and 105 Gy gamma-rays, the optical transmission of the irradiated crystal decreases by less than 4.8 and 8.0%, respectively. These values are comparable with those published earlier (Kozma et al., 1993) for CeF3 scintillation crystal of large volume. The measurement of transmission 15 days after 105 Gy irradiations showed the complete recovery of both examined tungstate crystals.
Fig. 3. Comparison of absorption coecients.
380
P. Kozma et al. / Radiation Physics and Chemistry 59 (2000) 377±380
Table 2 Transmission at peak emission Dose (Gy)
PbWO4 #1 (480 nm), %
PbWO4 #2 (480 nm), %
CdWO4 (470 nm), %
CeF3 (375 nm), %
0 104 105
70.0 59.5 50.5
72.0 67.0 63.5
77.5 74.5 71.5
82.8 80.0 74.5
Table 3 Degradation of transmission at peak emission Dose (Gy)
PbWO4 #1 (480 nm), %
PbWO4 #2 (480 nm), %
CdWO4 (470 nm), %
CeF3 (375 nm), %
104 105
15.0 27.5
7.5 12.5
4.8 8.0
2.8 10.0
References Kozma, P., Bajgar, R., Kozma Jr., P., 1997. Radiation resistivity of PbWO4 crystals. In: Zhiwen, Yin, et al. (Eds.), Proc. of the Int. Conf. SCINT'97, Shanghai, People's Republic of China, Sept. 22±26. CAS Shanghai Branch Press, p. 248. Kozma, P., Afanasiev, S., Malakhov, A., Povtoreiko, A., 1993. A cerium ¯uoride scintillator coupled to a FEU-140 photomultiplier. Nucl. Instr. and Meth. A328, 599±600.
Lecoq, P., 1997. The challenge of new scintillator development for high energy physics. In: Zhiwen, Yin, et al. (Eds.), Proc. of the Int. Conf. SCINT'97, Shanghai, People's Republic of China, Sept. 22±26. CAS Shanghai Branch Press, p. 13. Lu, Zusheng, Mao, Chengsheng, Tang, Xiaowei, 1997. Application of scintillation crystals in nuclear medicine. In: Zhiwen, Yin, et al. (Eds.), Proc. of the Conf. SCINT'97, Shanghai, People's Republic of China, Sept. 22±26. CAS Shanghai Branch Press, p. 18.