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Investigation of beam uniformity in industrial electron accelerator
Radiation Measurements 34 (2001) 609–613
www.elsevier.com/locate/radmeas
Investigation of beam uniformity in industrial electron accelerator F. Ziaiea; b; c;∗ , H. Afarideha , S.M. Hadji-Saeidc , S.A. Durranid a Nuclear
Research Center for Agriculture and Medicine, PO Box 31585-4395, Karaj, Iran Kabir University of Technology, Physic Department, PO Box 15875-4413, Tehran, Iran c Yazd Radiation Processing Center, PO Box 89175-389, Yazd, Iran d School of Physics & Space Research, University of Birmingham, Birmingham B15 2TT, UK
b Amir
Received 28 August 2000; received in revised form 4 January 2001; accepted 21 March 2001
Abstract In this paper the performances of the industrial electron beams processing, with 5 and 10 MeV energies, has been investigated by measuring two-dimensional dose distribution in electron beam pro3le. Large volume of absorbing materials with densities 0.5 and 1 g=cm3 , which are wood and polyethylene, respectively, are used as the irradiated materials. On the other hand the mentioned measurement are also performed for X-ray (Bremsstrahlung) beam that were converted by interaction of electron with a high power X-ray target. The experiments have been performed using several types of 3lm dosimeters such as PVB, CTA and FWT. These dosimeters are used for beam pro3le measurement and precise dose evaluation. The obtained results clearly show that the electron beam emerging out from scanning horn has a good uniformity along the electron beam pro3le. c 2001 Elsevier Science Ltd. All rights reserved. Keywords: Electron beam; X-ray; Bremsstrahlung; Beam uniformity; Beam pro3le
1. Introduction The recent extensive advances made in electron accelerators for processing have led to expansion of application 3elds in radiation processing. The requirement in radiation measurement and monitoring have been increased and diversi3ed in electron radiation processing, especially in research and developing stages. An electron irradiation center for research and industrial application of the electron beam processing technology was established at Yazd Radiation Processing Center (YRPC) at 1997. A 5 and 10 MeV, 100 kW electron accelerator, Rhodotron TT200 type, already has proved to be stable at 250 kW for many hours. The machine is also equipped by ∗ Corresponding author. Atomic Organization of Iran, Nuclear Research Center for Agriculture and Medicine, PO Box 31585-4395, Karaj, Iran. Tel.: +98-261-436397; fax: +98-261411105. E-mail address: [email protected] (F. Ziaie).
a scanning horn with a scan width of 100 cm, at a scan frequency of 100 Hz. Facility layout and items for commercial irradiation applications and also the radiation dosimetry system preparation and construction, is being planned or is under way. The facility consists of the electron accelerator machine, Bremsstrahlung target and a variable-speed conveyor, to pass the materials through the swept beam. The operation of the system is fully controlled by a personal computer for client’s order, electron beam characteristics and conveyor speed. These are to create the interested eIects into the products, ordered to irradiation. 2. Dosimeters used in measurements In processing electron accelerators, 3lm dosimeters are the most eIective means of directly obtaining information on various dose pro3les in irradiated materials. We have applied the CTA dosimeter (supplied by Fuji Photo Film Co., Japan) for various requirements in the electron irradiation technique
c 2001 Elsevier Science Ltd. All rights reserved. 1350-4487/01/$ - see front matter PII: S 1 3 5 0 - 4 4 8 7 ( 0 1 ) 0 0 2 3 9 - 6
610
F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613
(Tamura et al., 1981, Tanaka et al., 1984 and Tanaka et al., 1985). The CTA dosimeter has a linear response with a dose up to 150 kGy and CTA 3lm is in the form of a long tape (thickness: 0:125 mm, width: 8 mm). These advantages enable the dose distribution to be traced automatically and directly along the CTA tape. The optical density change per unit dose does not depend on the temperature and humidity during irradiation at dose rates higher than 1 MGy=h, which are typical for electron radiation processing (Tanaka et al., 1985). Two other types of radiochromic 3lms, namely PVB containing pararosaniline cyanide similar to those developed in RisH (McLaughlin et al., 1977; Janovsky, 1985) and FWT-60, were prepared and used. The PVB dosimeter has a linear response with a dose up to 80 kGy and is in the form of a long tape (thickness: 20 m, width: 3 cm). For the electron-irradiated CTA radiochromic 3lm, the 3nal colour developed within a few hours while for PVB 3lm both after electron and gamma irradiation some additional absorbance formation continued for several days (Janovsky, 1985). To accelerate this process the recom◦ mended heat treatment, 5 min at 60 C, was applied for PVB 3lms (Chappas, 1981). The CTA 3lm was evaluated by
Fig. 1. a. Scanning horn and the 3lm dosimeter arrangements for electron beam irradiation; b. Scanning horn, X-ray target and the 3lm dosimeter arrangements for X-ray irradiation.
Fig. 2. a. Dose distribution along the scanning direction for 5 MeV, 0:2 mA electron-beam; b. Dose distribution along the scanning direction for 10 MeV, 0:2 mA electron-beam; c. Dose distribution along the scanning direction for 5 MeV, 8 mA e=X-ray beam; d. Dose distribution along the scanning direction for 10 MeV, 2 mA e=X-ray beam.
F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613
611
Fig. 3. a. Dose distribution along the conveyor direction for 10 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); b. Dose distribution along the scanning direction for 10 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); c. Dose distribution along the conveyor direction for 10 MeV, 4 mA e=X-ray beam, in wood phantom depths (as shown on the graph in cm); d. Dose distribution along the scanning direction for 10 MeV, 4 mA e=X-ray beam, in wood phantom depths (as shown on the graph in cm); e. Dose distribution along the conveyor direction for 5 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); f. Dose distribution along the scanning direction for 5 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); g. Depth-dose distribution for 5 and 10 MeV e=X-ray beams, in wood and polyethylene phantom.
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F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613
can be reduced by correcting the radiation-induced optical density for thickness. 3. Experimental
Fig. 4. Schema of the back scattering eIect from X-ray target.
In preparation for the evaluation program in YRPC, some measurements were made using the 5 and 10 MeV electron and X-ray beams. The objective here was to devise experimental procedures and to obtain some data on beam pro3le and dose distribution in some materials. The target was 19 cm below the beam window and distance to the phantom surface are indicated in the 3gures as the h-value. Large volume of foodstuI materials was simulated by stacking sheets of wood or polyethylene as the irradiation phantom. Bulk density of these materials, are 0.5 and 1 g=cm3 , respectively. The sheets size were 45 cm × 80 cm, and 0.5, 1 or 2 cm thick. Dosimeters were located on a polyethylene plane for surface dose evaluation (Figs. 1a and b) and the related results are shown in Figs. 2a–d. Also dosimeter strips in cross form were spaced in depth, in order to obtain the three-dimensional dose distributions within the absorbing materials. Stationary exposures of the thick stacks, centered under the scanning horn or X-ray target were made. Dose distribution in conveyor and scanning direction as well as the depth–dose curve for electrons and X-ray beams are presented in Figs. 3a–g. On the other hand the backscattering of the electron beam from the X-ray target are investigated by using the long strip 3lm dosimeter putting under the X-ray beam along the conveyor direction (Fig. 4). Figs. 5a and b show the backscattering eIect for the 5 and 10 MeV electron beams. 4. Conclusion
Fig. 5. a. Dose distribution along the conveyor direction for 5 MeV, 8 mA e=X-ray beam; b. Dose distribution along the conveyor direction for 10 MeV, 8 mA e=X-ray beam.
measuring the radiation-induced absorbance at 280 nm, where this value for the PVB 3lm is 554 nm. Commonly available radiochromic 3lm FWT-60 (from Far West Technology, Inc., Gleta, USA) was used to check the reliability of the measurements. Absorbance of the irradiated 3lm was measured at 600 or 604 nm, which for electron radiation about 6 h after irradiation, is suMcient for full colour development (Chappas, 1981). A UV spectrophotometer, SPECTRONIC GENESYS made by USA, is commonly used as the readout system for the dosimeters. The Nuctuation of optical density along the unirradiated 3lm dosimeters usually increases with dose. Increment of the Nuctuation is chieNy due to the Nuctuation of thickness of the 3lms. It
Figs. 2 and 3 show an acceptable dose uniformity in surface and also in the layers of the materials. Especially the electron beam had a good uniformity, being uniform within 2% over the diameter of the calorimeter disk. This is a very important factor in every radiation-processing center in calibration of the 3lm dosimeters. On the other hand from Fig. 5a, one can 3nd a little back scattering eIect due to the 5 MeV electrons reNected from the X-ray target. This is because of the low energy in comparison to 10 MeV, which according to Fig. 5b does not show the same eIect.
References Chappas, W., 1981. Temperature and humidity eIects on the response radiochromic dye 3lms. Radiat. Phys. Chem. 18 (5 – 6), 1017–1021. Janovsky, I., 1985. Dosimetry methods applied to irradiation with Tesla-4 MeV linear accelerator. Vienna, IAEA-SM-272=37, 307–316.
F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613 McLaughlin, W.L., Miller, A., Fidans, S., Pejtersen, K., Batsberg Pedersen, W., 1977. Radiochromic plastic 3lms for accurate measurements of radiation absorbed doses and dose distributions. Radiat. Phys. Chem. 10 (2), 119–127. Tamura, N., Tanaka, R., Mitomo, S., Matsuda, K., Nagai, S., 1981. Properties of cellulose triacetate dose meters. Radiat. Phys. Chem. 18, 977–985.
613
Tanaka, R., Mitomo, S., Tamura, N., 1984. EIect of temperature, relative humidity and dose rate on the sensitivity of cellulose triacetate dosimeters to electron and gamma-rays. Int. J. Appl. Radiat. Isot. 35, 875–881. Tanaka, R., Sunuga, H., Agematsu, T., 1985. Methods for measuring dose and beam pro3les of processing electron accelerators. IAEA-SM-272=18, 317–331.
www.elsevier.com/locate/radmeas
Investigation of beam uniformity in industrial electron accelerator F. Ziaiea; b; c;∗ , H. Afarideha , S.M. Hadji-Saeidc , S.A. Durranid a Nuclear
Research Center for Agriculture and Medicine, PO Box 31585-4395, Karaj, Iran Kabir University of Technology, Physic Department, PO Box 15875-4413, Tehran, Iran c Yazd Radiation Processing Center, PO Box 89175-389, Yazd, Iran d School of Physics & Space Research, University of Birmingham, Birmingham B15 2TT, UK
b Amir
Received 28 August 2000; received in revised form 4 January 2001; accepted 21 March 2001
Abstract In this paper the performances of the industrial electron beams processing, with 5 and 10 MeV energies, has been investigated by measuring two-dimensional dose distribution in electron beam pro3le. Large volume of absorbing materials with densities 0.5 and 1 g=cm3 , which are wood and polyethylene, respectively, are used as the irradiated materials. On the other hand the mentioned measurement are also performed for X-ray (Bremsstrahlung) beam that were converted by interaction of electron with a high power X-ray target. The experiments have been performed using several types of 3lm dosimeters such as PVB, CTA and FWT. These dosimeters are used for beam pro3le measurement and precise dose evaluation. The obtained results clearly show that the electron beam emerging out from scanning horn has a good uniformity along the electron beam pro3le. c 2001 Elsevier Science Ltd. All rights reserved. Keywords: Electron beam; X-ray; Bremsstrahlung; Beam uniformity; Beam pro3le
1. Introduction The recent extensive advances made in electron accelerators for processing have led to expansion of application 3elds in radiation processing. The requirement in radiation measurement and monitoring have been increased and diversi3ed in electron radiation processing, especially in research and developing stages. An electron irradiation center for research and industrial application of the electron beam processing technology was established at Yazd Radiation Processing Center (YRPC) at 1997. A 5 and 10 MeV, 100 kW electron accelerator, Rhodotron TT200 type, already has proved to be stable at 250 kW for many hours. The machine is also equipped by ∗ Corresponding author. Atomic Organization of Iran, Nuclear Research Center for Agriculture and Medicine, PO Box 31585-4395, Karaj, Iran. Tel.: +98-261-436397; fax: +98-261411105. E-mail address: [email protected] (F. Ziaie).
a scanning horn with a scan width of 100 cm, at a scan frequency of 100 Hz. Facility layout and items for commercial irradiation applications and also the radiation dosimetry system preparation and construction, is being planned or is under way. The facility consists of the electron accelerator machine, Bremsstrahlung target and a variable-speed conveyor, to pass the materials through the swept beam. The operation of the system is fully controlled by a personal computer for client’s order, electron beam characteristics and conveyor speed. These are to create the interested eIects into the products, ordered to irradiation. 2. Dosimeters used in measurements In processing electron accelerators, 3lm dosimeters are the most eIective means of directly obtaining information on various dose pro3les in irradiated materials. We have applied the CTA dosimeter (supplied by Fuji Photo Film Co., Japan) for various requirements in the electron irradiation technique
c 2001 Elsevier Science Ltd. All rights reserved. 1350-4487/01/$ - see front matter PII: S 1 3 5 0 - 4 4 8 7 ( 0 1 ) 0 0 2 3 9 - 6
610
F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613
(Tamura et al., 1981, Tanaka et al., 1984 and Tanaka et al., 1985). The CTA dosimeter has a linear response with a dose up to 150 kGy and CTA 3lm is in the form of a long tape (thickness: 0:125 mm, width: 8 mm). These advantages enable the dose distribution to be traced automatically and directly along the CTA tape. The optical density change per unit dose does not depend on the temperature and humidity during irradiation at dose rates higher than 1 MGy=h, which are typical for electron radiation processing (Tanaka et al., 1985). Two other types of radiochromic 3lms, namely PVB containing pararosaniline cyanide similar to those developed in RisH (McLaughlin et al., 1977; Janovsky, 1985) and FWT-60, were prepared and used. The PVB dosimeter has a linear response with a dose up to 80 kGy and is in the form of a long tape (thickness: 20 m, width: 3 cm). For the electron-irradiated CTA radiochromic 3lm, the 3nal colour developed within a few hours while for PVB 3lm both after electron and gamma irradiation some additional absorbance formation continued for several days (Janovsky, 1985). To accelerate this process the recom◦ mended heat treatment, 5 min at 60 C, was applied for PVB 3lms (Chappas, 1981). The CTA 3lm was evaluated by
Fig. 1. a. Scanning horn and the 3lm dosimeter arrangements for electron beam irradiation; b. Scanning horn, X-ray target and the 3lm dosimeter arrangements for X-ray irradiation.
Fig. 2. a. Dose distribution along the scanning direction for 5 MeV, 0:2 mA electron-beam; b. Dose distribution along the scanning direction for 10 MeV, 0:2 mA electron-beam; c. Dose distribution along the scanning direction for 5 MeV, 8 mA e=X-ray beam; d. Dose distribution along the scanning direction for 10 MeV, 2 mA e=X-ray beam.
F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613
611
Fig. 3. a. Dose distribution along the conveyor direction for 10 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); b. Dose distribution along the scanning direction for 10 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); c. Dose distribution along the conveyor direction for 10 MeV, 4 mA e=X-ray beam, in wood phantom depths (as shown on the graph in cm); d. Dose distribution along the scanning direction for 10 MeV, 4 mA e=X-ray beam, in wood phantom depths (as shown on the graph in cm); e. Dose distribution along the conveyor direction for 5 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); f. Dose distribution along the scanning direction for 5 MeV, 4 mA e=X-ray beam, in polyethylene phantom depths (as shown on the graph in cm); g. Depth-dose distribution for 5 and 10 MeV e=X-ray beams, in wood and polyethylene phantom.
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F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613
can be reduced by correcting the radiation-induced optical density for thickness. 3. Experimental
Fig. 4. Schema of the back scattering eIect from X-ray target.
In preparation for the evaluation program in YRPC, some measurements were made using the 5 and 10 MeV electron and X-ray beams. The objective here was to devise experimental procedures and to obtain some data on beam pro3le and dose distribution in some materials. The target was 19 cm below the beam window and distance to the phantom surface are indicated in the 3gures as the h-value. Large volume of foodstuI materials was simulated by stacking sheets of wood or polyethylene as the irradiation phantom. Bulk density of these materials, are 0.5 and 1 g=cm3 , respectively. The sheets size were 45 cm × 80 cm, and 0.5, 1 or 2 cm thick. Dosimeters were located on a polyethylene plane for surface dose evaluation (Figs. 1a and b) and the related results are shown in Figs. 2a–d. Also dosimeter strips in cross form were spaced in depth, in order to obtain the three-dimensional dose distributions within the absorbing materials. Stationary exposures of the thick stacks, centered under the scanning horn or X-ray target were made. Dose distribution in conveyor and scanning direction as well as the depth–dose curve for electrons and X-ray beams are presented in Figs. 3a–g. On the other hand the backscattering of the electron beam from the X-ray target are investigated by using the long strip 3lm dosimeter putting under the X-ray beam along the conveyor direction (Fig. 4). Figs. 5a and b show the backscattering eIect for the 5 and 10 MeV electron beams. 4. Conclusion
Fig. 5. a. Dose distribution along the conveyor direction for 5 MeV, 8 mA e=X-ray beam; b. Dose distribution along the conveyor direction for 10 MeV, 8 mA e=X-ray beam.
measuring the radiation-induced absorbance at 280 nm, where this value for the PVB 3lm is 554 nm. Commonly available radiochromic 3lm FWT-60 (from Far West Technology, Inc., Gleta, USA) was used to check the reliability of the measurements. Absorbance of the irradiated 3lm was measured at 600 or 604 nm, which for electron radiation about 6 h after irradiation, is suMcient for full colour development (Chappas, 1981). A UV spectrophotometer, SPECTRONIC GENESYS made by USA, is commonly used as the readout system for the dosimeters. The Nuctuation of optical density along the unirradiated 3lm dosimeters usually increases with dose. Increment of the Nuctuation is chieNy due to the Nuctuation of thickness of the 3lms. It
Figs. 2 and 3 show an acceptable dose uniformity in surface and also in the layers of the materials. Especially the electron beam had a good uniformity, being uniform within 2% over the diameter of the calorimeter disk. This is a very important factor in every radiation-processing center in calibration of the 3lm dosimeters. On the other hand from Fig. 5a, one can 3nd a little back scattering eIect due to the 5 MeV electrons reNected from the X-ray target. This is because of the low energy in comparison to 10 MeV, which according to Fig. 5b does not show the same eIect.
References Chappas, W., 1981. Temperature and humidity eIects on the response radiochromic dye 3lms. Radiat. Phys. Chem. 18 (5 – 6), 1017–1021. Janovsky, I., 1985. Dosimetry methods applied to irradiation with Tesla-4 MeV linear accelerator. Vienna, IAEA-SM-272=37, 307–316.
F. Ziaie et al. / Radiation Measurements 34 (2001) 609–613 McLaughlin, W.L., Miller, A., Fidans, S., Pejtersen, K., Batsberg Pedersen, W., 1977. Radiochromic plastic 3lms for accurate measurements of radiation absorbed doses and dose distributions. Radiat. Phys. Chem. 10 (2), 119–127. Tamura, N., Tanaka, R., Mitomo, S., Matsuda, K., Nagai, S., 1981. Properties of cellulose triacetate dose meters. Radiat. Phys. Chem. 18, 977–985.
613
Tanaka, R., Mitomo, S., Tamura, N., 1984. EIect of temperature, relative humidity and dose rate on the sensitivity of cellulose triacetate dosimeters to electron and gamma-rays. Int. J. Appl. Radiat. Isot. 35, 875–881. Tanaka, R., Sunuga, H., Agematsu, T., 1985. Methods for measuring dose and beam pro3les of processing electron accelerators. IAEA-SM-272=18, 317–331.