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Results on electron irradiated Fricke solutions at low temperatures
Nuclear Instruments and Methods in Physics Research B 161±163 (2000) 387±389
www.elsevier.nl/locate/nimb
Results on electron irradiated Fricke solutions at low temperatures A. Hategan a
a,*
, D. Martin a, C. Butan a, L.M. Popescu b, A. Popescu a, C. Oproiu
a
INFLPR, Institute of Atomic Physics, Electron Accelerators Lab., P.O. Box MG-36, R-76900 Magurele, Bucharest, Romania b Institute of Environmental Research and Engineering, P.O. Box 11-2 Bucharest, Romania
Abstract This work presents results concerning the possibility of extending Fricke dosimetry at )196°C and )5°C irradiation temperatures. Frozen samples of Fricke solution at )196°C and, respectively )5°C, and samples of Fricke solution at room temperature were simultaneously irradiated with the 5 MeV electron beam of a linear accelerator. Our results showed for the frozen irradiated Fricke solutions apparent dose values with approximately one order of magnitude smaller than the real values, as obtained with liquid Fricke solution, in the case of )196°C irradiation temperature, and dose values approximately reduced by a factor of two, in the case of )5°C. The explanation of these results is based upon the low rate of migration and the local recombination of the water radicals induced by radiation, which are involved in the reaction Fe2 ! Fe3 . The apparent dose values obtained for the )5°C and )196°C frozen Fricke solutions showed a linear dependence with the real dose values, indicating that the data obtained might be used to create a calibrating curve. More data will be collected in order to test the accuracy and the reproducibility of the system. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 87.66 Ff; 87.53 Hv; 87.58 Sp Keywords: Fricke; Chemical dosimetry
1. Introduction It is important to determine with accuracy the amount of energy deposited in biological samples by radiation (the dose), in order to estimate the eects of radiation at molecular level. The dose absorbed by biological samples might be preferably estimated with a dosimetric system that is similar to the biological material. From this point of view, Fricke dosimetry, being appropriate in *
Corresponding author. Tel.: +4017804785; +4014231791. E-mail address: ahateg@i®n.nipne.ro (A. Hategan).
fax:
estimating the dose obtained in aqueous systems, is also useful for biological samples, which mainly consist of water [1]. Fricke solution consists of a feric sulphate acid solution and Fricke dosimetry is based on a reaction induced by water radicals, as are also the reactions induced by radiation in biological samples. The geometry of the irradiated system plays a key role in estimating the dose and Fricke dosimetry it makes possible to determine the dose in the same geometry as the system to be irradiated [2±7]. In the case of frozen biological samples, the quantity of primary radiation products formed will be the same as that in the case of liquid
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 8 1 8 - 6
388
A. Hategan et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 387±389
biological samples, at room temperature (only their mobility is grossly dierent), and from this point of view, the Fricke dosimetry should be also appropriate in the frozen state [1]. Another advantage of using Fricke dosimetry is that it is a rapid way to estimate the dose, necessary for the in-time analysis of biological samples during the experiment. The aim of this work is to test the possibility of using Fricke dosimetry at )196°C and )5°C temperatures, in order to estimate the dose absorbed by frozen biological samples. 2. Theory Fricke dosimetry is based on the radiolitic oxidation of Fe2 in Fe3 in acid solution and in the presence of oxygen. Fricke solution has the following composition: 10ÿ3 M FeSO4 , 0.8 N H2 SO4 The spectrophotometric determination of the concentration of Fe3 induced by radiation allows to calculate the dose absorbed in the sample [8]. The simpli®ed scheme of the reactions that take place is [4]:
linear transfer of energy and of the energy of the radiation, independent on temperature, with a good reproducibility and stable before, during and after irradiation [3,4]. No chemical system was found to exhibit all these properties at the same time, but, in particular dose ranges, systems were found which full®l most of these criteria. The Fricke dosimeter is independent on the dose rate up to 108 Gy/min, and has an accuracy of 1±2% in the dose range of 0±400 Gy. It has also a very weak dependence on temperature (the temperature coecient is 10ÿ3 Kÿ1 ) [4]. Because of its properties is considered a reference dosimeter [2±4]. Fricke dosimetry, being appropriate in estimating the dose obtained in aqueous systems, is also useful for estimating dose in biological samples, which are almost water equivalent. The idea of the experiment is to test if a calibration curve can be obtained between the apparent dose values obtained from frozen Fricke solutions and the real values obtained from liquid Fricke solutions, irradiated at room temperature, in order to estimate the dose absorbed by frozen biological samples.
_ ! Fe3 OH _ ÿ; Fe2 OH _ 2; _ O2 ! HO H _ 2H _ ! Fe3 H2 O2 ; Fe2 HO _ OH _ ÿ: Fe2 H2 O2 ! Fe3 OH The radiochemical eciency (number of elementary chemical species produced by radiation for 100 eV energy absorbed) is, in our case: G Fe2 G OH 3G H 2G H2 O2 ; and the dose can be estimated according to: D 9:64 106 C= qG; where q is the density of solution (g/cm3 ) and C is the molar concentration of Fe3 , which is determined spectrophotometrically. An ideal chemical dosimeter is a chemical system with the following properties: the radiochemical eciency has to be constant with the dose, independent of the dose rate, independent of the
3. Experimental results and conclusions Frozen samples of Fricke solution (10ÿ3 M FeSO4 , 0.8 N H2 SO4 ) at )196°C and, respectively )5°C, and samples of Fricke solution at room temperature were simultaneous irradiated with the 5 MeV electron beam of a linear accelerator, with the following parameters: 5±10 MeV energy of the electron beam, average intensity of 5±10 lA, frequency of the pulses 100 MHz, time of a pulse 5±10 ls. The pair samples (frozen Fricke solutions at )196°C or, respectively, 5°C and liquid Fricke solutions, at room temperature) were placed in a vertical geometry, at 45 cm under the de¯ector magnet of the linear accelerator. A 1 mm aluminium foil was placed on the top of the samples. They were placed in the same irradiation geometry as the biological samples that have to be irradiated. Our experimental results are plotted in Fig. 1 (for the )196°C irradiation temperature) and Fig. 2 (in the case of )5°C frozen samples). We tested the
A. Hategan et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 387±389
Fig. 1. Correlation between electron dose estimated with normal Fricke solution and )196°C frozen Fricke solution.
Fig. 2. Correlation between electron dose estimated with normal Fricke solution and )5°C frozen Fricke solution.
possibility of calibrating the apparent dose values obtained with frozen Fricke solutions, by reporting them to real doses, which were obtained with Fricke solution at room temperature. The data presented in Fig. 2 showed for the )5°C irradiated Fricke solutions the dose values were approximately 50% of the values estimated with Fricke solution at room temperature. The experimental data obtained here can be ®tted with a linear curve (correlation coecient 0.97), and might constitute a calibrating curve for the frozen Fricke samples.
389
More tests should and will be done, however, in order to determine the measurement uncertainty for the experimental data obtained. The data presented in Fig. 1 showed for the )196°C irradiated Fricke solution dose values which are one order of magnitude smaller than the values obtained from the simultaneous irradiated Fricke solutions at room temperature. Our data are in agreement with the experimental values for the radiochemical eciency of frozen water, which was found to decrease by one order of magnitude from 20°C to )200°C [2]. The explanation of our results is based on the low rate of migration of the water radicals induced by radiation, which are involved in the reaction Fe2 ! Fe3 . The radiochemical yield might also be modi®ed at this low temperature because of the reduced rate of migration of the water radicals induced and their local recombination and because of the absence of oxygen in the solution [2±4] in the case of frozen samples. The data obtained can be ®tted with a linear curve (correlation coecient 0.97), and might constitute a calibrating curve for the )196°C frozen Fricke samples. The )196°C frozen Fricke solutions might be tested for consisting a dosymetric system for larger doses, but for this test to be done, the real dose values (which exceed the Fricke dosimeter range) have to be estimated with another dosimetric system. References [1] E. Kempner, Quart. Rev. Biophys. 26 (1993) 27. [2] M. Fiti, in: Acad. RSR (Ed.), Actiunea radiatiilor ionizante asupra apei si a solutiilor apoase, Bucuresti, 1967. [3] M. Fiti, in: Dozimetria chimica a radiatiilor ionizante, Acad. RSR, Bucuresti, 1973. [4] M. Oncescu, I. Panaitescu, in: Dozimetria si ecranarea radiatiilor roentgen si gamma, Acad. Rom, Bucuresti, 1992. [5] N.W. Holm, R.J. Berry, in: Manual on Radiation Dosimetry, Dekker, New York, 1970. [6] K. Schested, E. Bjergbakke, N.W. Holm, H. Fricke, IAEASM-160/30, 1973. [7] W.L. McLaughlin, A.W. Boyd, K.H. Chadwick, I.C. McDonald, A. Miller, in: Dosimetry for Radiation Processing, Taylor & Francis, London, 1989. [8] M.B. Podgorsk, L.J. Schreiner, Med. Phys. 19 (1) (1992) 88.
www.elsevier.nl/locate/nimb
Results on electron irradiated Fricke solutions at low temperatures A. Hategan a
a,*
, D. Martin a, C. Butan a, L.M. Popescu b, A. Popescu a, C. Oproiu
a
INFLPR, Institute of Atomic Physics, Electron Accelerators Lab., P.O. Box MG-36, R-76900 Magurele, Bucharest, Romania b Institute of Environmental Research and Engineering, P.O. Box 11-2 Bucharest, Romania
Abstract This work presents results concerning the possibility of extending Fricke dosimetry at )196°C and )5°C irradiation temperatures. Frozen samples of Fricke solution at )196°C and, respectively )5°C, and samples of Fricke solution at room temperature were simultaneously irradiated with the 5 MeV electron beam of a linear accelerator. Our results showed for the frozen irradiated Fricke solutions apparent dose values with approximately one order of magnitude smaller than the real values, as obtained with liquid Fricke solution, in the case of )196°C irradiation temperature, and dose values approximately reduced by a factor of two, in the case of )5°C. The explanation of these results is based upon the low rate of migration and the local recombination of the water radicals induced by radiation, which are involved in the reaction Fe2 ! Fe3 . The apparent dose values obtained for the )5°C and )196°C frozen Fricke solutions showed a linear dependence with the real dose values, indicating that the data obtained might be used to create a calibrating curve. More data will be collected in order to test the accuracy and the reproducibility of the system. Ó 2000 Elsevier Science B.V. All rights reserved. PACS: 87.66 Ff; 87.53 Hv; 87.58 Sp Keywords: Fricke; Chemical dosimetry
1. Introduction It is important to determine with accuracy the amount of energy deposited in biological samples by radiation (the dose), in order to estimate the eects of radiation at molecular level. The dose absorbed by biological samples might be preferably estimated with a dosimetric system that is similar to the biological material. From this point of view, Fricke dosimetry, being appropriate in *
Corresponding author. Tel.: +4017804785; +4014231791. E-mail address: ahateg@i®n.nipne.ro (A. Hategan).
fax:
estimating the dose obtained in aqueous systems, is also useful for biological samples, which mainly consist of water [1]. Fricke solution consists of a feric sulphate acid solution and Fricke dosimetry is based on a reaction induced by water radicals, as are also the reactions induced by radiation in biological samples. The geometry of the irradiated system plays a key role in estimating the dose and Fricke dosimetry it makes possible to determine the dose in the same geometry as the system to be irradiated [2±7]. In the case of frozen biological samples, the quantity of primary radiation products formed will be the same as that in the case of liquid
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 8 1 8 - 6
388
A. Hategan et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 387±389
biological samples, at room temperature (only their mobility is grossly dierent), and from this point of view, the Fricke dosimetry should be also appropriate in the frozen state [1]. Another advantage of using Fricke dosimetry is that it is a rapid way to estimate the dose, necessary for the in-time analysis of biological samples during the experiment. The aim of this work is to test the possibility of using Fricke dosimetry at )196°C and )5°C temperatures, in order to estimate the dose absorbed by frozen biological samples. 2. Theory Fricke dosimetry is based on the radiolitic oxidation of Fe2 in Fe3 in acid solution and in the presence of oxygen. Fricke solution has the following composition: 10ÿ3 M FeSO4 , 0.8 N H2 SO4 The spectrophotometric determination of the concentration of Fe3 induced by radiation allows to calculate the dose absorbed in the sample [8]. The simpli®ed scheme of the reactions that take place is [4]:
linear transfer of energy and of the energy of the radiation, independent on temperature, with a good reproducibility and stable before, during and after irradiation [3,4]. No chemical system was found to exhibit all these properties at the same time, but, in particular dose ranges, systems were found which full®l most of these criteria. The Fricke dosimeter is independent on the dose rate up to 108 Gy/min, and has an accuracy of 1±2% in the dose range of 0±400 Gy. It has also a very weak dependence on temperature (the temperature coecient is 10ÿ3 Kÿ1 ) [4]. Because of its properties is considered a reference dosimeter [2±4]. Fricke dosimetry, being appropriate in estimating the dose obtained in aqueous systems, is also useful for estimating dose in biological samples, which are almost water equivalent. The idea of the experiment is to test if a calibration curve can be obtained between the apparent dose values obtained from frozen Fricke solutions and the real values obtained from liquid Fricke solutions, irradiated at room temperature, in order to estimate the dose absorbed by frozen biological samples.
_ ! Fe3 OH _ ÿ; Fe2 OH _ 2; _ O2 ! HO H _ 2H _ ! Fe3 H2 O2 ; Fe2 HO _ OH _ ÿ: Fe2 H2 O2 ! Fe3 OH The radiochemical eciency (number of elementary chemical species produced by radiation for 100 eV energy absorbed) is, in our case: G Fe2 G OH 3G H 2G H2 O2 ; and the dose can be estimated according to: D 9:64 106 C= qG; where q is the density of solution (g/cm3 ) and C is the molar concentration of Fe3 , which is determined spectrophotometrically. An ideal chemical dosimeter is a chemical system with the following properties: the radiochemical eciency has to be constant with the dose, independent of the dose rate, independent of the
3. Experimental results and conclusions Frozen samples of Fricke solution (10ÿ3 M FeSO4 , 0.8 N H2 SO4 ) at )196°C and, respectively )5°C, and samples of Fricke solution at room temperature were simultaneous irradiated with the 5 MeV electron beam of a linear accelerator, with the following parameters: 5±10 MeV energy of the electron beam, average intensity of 5±10 lA, frequency of the pulses 100 MHz, time of a pulse 5±10 ls. The pair samples (frozen Fricke solutions at )196°C or, respectively, 5°C and liquid Fricke solutions, at room temperature) were placed in a vertical geometry, at 45 cm under the de¯ector magnet of the linear accelerator. A 1 mm aluminium foil was placed on the top of the samples. They were placed in the same irradiation geometry as the biological samples that have to be irradiated. Our experimental results are plotted in Fig. 1 (for the )196°C irradiation temperature) and Fig. 2 (in the case of )5°C frozen samples). We tested the
A. Hategan et al. / Nucl. Instr. and Meth. in Phys. Res. B 161±163 (2000) 387±389
Fig. 1. Correlation between electron dose estimated with normal Fricke solution and )196°C frozen Fricke solution.
Fig. 2. Correlation between electron dose estimated with normal Fricke solution and )5°C frozen Fricke solution.
possibility of calibrating the apparent dose values obtained with frozen Fricke solutions, by reporting them to real doses, which were obtained with Fricke solution at room temperature. The data presented in Fig. 2 showed for the )5°C irradiated Fricke solutions the dose values were approximately 50% of the values estimated with Fricke solution at room temperature. The experimental data obtained here can be ®tted with a linear curve (correlation coecient 0.97), and might constitute a calibrating curve for the frozen Fricke samples.
389
More tests should and will be done, however, in order to determine the measurement uncertainty for the experimental data obtained. The data presented in Fig. 1 showed for the )196°C irradiated Fricke solution dose values which are one order of magnitude smaller than the values obtained from the simultaneous irradiated Fricke solutions at room temperature. Our data are in agreement with the experimental values for the radiochemical eciency of frozen water, which was found to decrease by one order of magnitude from 20°C to )200°C [2]. The explanation of our results is based on the low rate of migration of the water radicals induced by radiation, which are involved in the reaction Fe2 ! Fe3 . The radiochemical yield might also be modi®ed at this low temperature because of the reduced rate of migration of the water radicals induced and their local recombination and because of the absence of oxygen in the solution [2±4] in the case of frozen samples. The data obtained can be ®tted with a linear curve (correlation coecient 0.97), and might constitute a calibrating curve for the )196°C frozen Fricke samples. The )196°C frozen Fricke solutions might be tested for consisting a dosymetric system for larger doses, but for this test to be done, the real dose values (which exceed the Fricke dosimeter range) have to be estimated with another dosimetric system. References [1] E. Kempner, Quart. Rev. Biophys. 26 (1993) 27. [2] M. Fiti, in: Acad. RSR (Ed.), Actiunea radiatiilor ionizante asupra apei si a solutiilor apoase, Bucuresti, 1967. [3] M. Fiti, in: Dozimetria chimica a radiatiilor ionizante, Acad. RSR, Bucuresti, 1973. [4] M. Oncescu, I. Panaitescu, in: Dozimetria si ecranarea radiatiilor roentgen si gamma, Acad. Rom, Bucuresti, 1992. [5] N.W. Holm, R.J. Berry, in: Manual on Radiation Dosimetry, Dekker, New York, 1970. [6] K. Schested, E. Bjergbakke, N.W. Holm, H. Fricke, IAEASM-160/30, 1973. [7] W.L. McLaughlin, A.W. Boyd, K.H. Chadwick, I.C. McDonald, A. Miller, in: Dosimetry for Radiation Processing, Taylor & Francis, London, 1989. [8] M.B. Podgorsk, L.J. Schreiner, Med. Phys. 19 (1) (1992) 88.