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Dependence of irradiation temperature in the response of iron salts
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Radiation Measurements 38 (2004) 455 – 458 www.elsevier.com/locate/radmeas
Dependence of irradiation temperature in the response of iron salts T. Mart"#neza , J. Lartiguea , D. Friasb , G. Sanchez-Mejoradac , A. Negr"on-Mendozad , S. Ramos-Bernald;∗ a Facultad
de Qu mica, UNAM, Ciudad Universitaria, C.P. 04510, M exico DF, Mexico de Ciencias Exatas e Tecnologicas, Universidad Estadual de Santa Cruz, Brazil c Facultad de Medicina, UNAM, Ciudad Universitaria, C.P. 04510, M
exico DF, Mexico d Instituto de Ciencias Nucleares, UNAM, A.P. 70-543, C.P. 04510, M
exico DF, Mexico
b Departamento
Received 15 November 2003; received in revised form 15 November 2003; accepted 25 January 2004
Abstract A potential dosimeter based on aqueous frozen solutions and solid-state salt are presented for the evaluation of the energy transferred during the interaction of high-energy radiation with matter at low temperature. The foundation of these dosimeters, both the solid state and the frozen solutions, is based on the measurement of the change of the iron oxidation state. The systems were irradiated with gamma radiation at di7erent doses (up to 10 MGy), and at di7erent temperatures (from 77 to 298 K). The irradiated samples were analysed by UV-spectroscopy and M=ossbauer spectroscopy. A theoretical model was developed for the chemical reactions system. This model reproduces the experimental e7ects produced by the irradiation in aqueous solutions of ferrous salt. The results showed that the response of the dosimeters depends on the irradiation temperature. At low-radiation doses, the response was linear. In particular, this work can be applied to low-temperature dosimetry can be specially applied to simulation experiments of extraterrestrial bodies, as well as in general to space research. c 2004 Published by Elsevier Ltd. Keywords: Temperature; Irradiation; Iron salts; Dosimetry
1. Introduction Energy is deposited in matter during its interaction with ionizing radiation. In general, the quantiBcation of this transferred energy is very important (Ramos-Bernal et al., 2000). This is specially the case when high-energy radiation interacts with living matter. These interactions are for example in personal dosimetry, incursion of humans into the radiation Beld of the outer space, and in the irradiation of living material. One important assumption for the evaluation of the energy deposited into the sample is that the dosimeter bears as much as possible the same conditions of the sample. Therefore for the cases mentioned above, it is ∗ Corresponding author. Tel.: +52-555-622-4672; fax: +52-5556-162-233. E-mail address: [email protected] (S. Ramos-Bernal).
c 2004 Published by Elsevier Ltd. 1350-4487/$ - see front matter doi:10.1016/j.radmeas.2004.01.034
necessary to perform low-temperature dosimetry. These types of measurements are relevant for laboratory simulation experiments related to some extraterrestrial conditions; say icy bodies, (Negron-Mendoza et al., 1994). In these experiments it is necessary to have a quantitative picture of the energy deposited into dosimeter at the same temperature of the icy body sample (Negron-Mendoza et al., 1994). On the other hand, aqueous solutions are important for dosimetry purposes due to the substantial amount of water in the human body. It is possible to extend the experience about the irradiation of liquids to the frozen solutions (Draganic and Draganic, 1971). However, di7usion of the reactive species, viscosity, and other properties make in general, frozen solutions more complex objects to study. The aim of the present work is (1) to study the irradiation of ferrous sulphate in solid state, and in frozen solutions. (2) To evaluate their behaviour below room temperature, and (3) to Bgure out its potential use as dosimetric systems
456
T. Mart nez et al. / Radiation Measurements 38 (2004) 455 – 458
for low-temperature irradiation. These systems were chosen because they are easy to prepare, as well as for their high sensitivity and stability. Their response is linear at room temperature and therefore we can make a comparison with the response at low temperature. Both the theoretical model and the experimental results, will allow us to evaluate the possible use of iron frozen solutions as a dosimeter.
2. Experimental procedures 2.1. Frozen solutions Chemicals and glassware were treated according to the standard procedures used in Radiation Chemistry (Draganic and Draganic, 1971). The water was triple distilled from an alkaline permanganate solution, from an acid solution of dichromate and the last distillation without adding any reagent. For this study, we used Baker reagent grade ferrous sulphate, sulphuric acid and sodium chloride. Solutions: The Iron salt dosimeter system (Fricke dosimeter) was used as described by Draganic and Draganic (1971). Solutions were in Pyrex cell inside of a Dewar Kask Blled with di7erent cooling agents (water, dry ice and liquid nitrogen). Solutions were frozen gradually to avoid that the glass containers break and to have the same type of crystal ice. The samples were irradiated in a 60 Co gamma source. The dose rate was 9:1 Gy=min. The doses were up to 600 Gy. 2.2. Solid-state iron sulphate Solid samples of heptahydrate ferrous sulphate were in closed glass tubes. Two sets were irradiated with doses from 0.5 to 10 MGy and from 0.2 to 1 MGy. 2.3. Analysis Frozen solutions: The samples were melted after irradiation and the temperature was adjusted to 25◦ C prior measurements. The ferric ions were measured spectrometrically at 304 nm. The molar extinction coeLcient for ferric ion was 2197 M−1 cm−1 at 25◦ C. The doses are based on the ferrous sulphate dosimeter at 25◦ C on the assumption of 15.6 ferric ions are formed by 100 eV absorbed in an air saturated solution. Solid samples: The analysis of these samples was carried out by M=ossbauer spectroscopy, using metal iron, ferric sulphate and ferrous sulphate as calibrators. The optimal thickness of the sample was 0:12324 g cm−2 , and the amount of FeSO4 :7H2 O was 0:623 g. The spectra were measured at room temperature. Measuring the areas of the peaks gave the amount of ferric ion in relation to the total amount of ferrous ion present in the sample. A computer program specially developed for the spectrum separation and Btting (MOSS BAS) is described in Martinez (1989).
2.4. The theoretical model The chemical reactions occurring in the aqueous system are also theoretically simulated in this work. This is carried out by presenting the chemical reactions as a set of di7erential equations of the sti7 type that represents the changes that are taking place in the sample. 2.4.1. Translation from reaction equations to di:erential equations The chemical reaction equations are expressed in a nomenclature very similar to that used by chemists. The program contains a translation part that, by analysing the reaction equations, identiBes, stores the names of the reactants, and stores the reaction constants belonging to the reaction equations. Then a two-dimensional matrix is constructed, which contains the information necessary for computing the right-hand side of the di7erential system. Each line in the matrix has n elements containing the address of the reactant Ri for which the derivative is to be computed, the stoichiometric constant njk , and the address for a rate constant kijk , the source term, and addresses for reactants Rj and Rk on the left side of the reaction equation. For each reactant in the reaction, system there is a line with n elements in the matrix. This matrix is used by the subroutine computing the right-hand side of the di7erential equation system and the Jacobian matrix for the system. 2.4.2. Balance equations The accurate solution of the di7erential equation system describing the chemical reactions requires an overall conservation of the mass balance. Two main factors are involved in the conservation of mass namely the reaction mechanism and the integration process. It must be pointed out that the formal stoichiometric balance needs not be the same as an atom-to-atom balance. The program recognizes each species individual letters and numbers. It is unnecessary to check the mass balance continuously, it is suLcient to do that at the start of the integration, i.e. at time t = 0. 3. Results and discussion 3.1. Frozen solutions Fig. 1 shows the response of iron salt in frozen solution irradiated at di7erent doses, and temperatures. The symbols are the experimental values and the lines are the values calculated by the model. The plots represent the change of the valence state of the divalent iron as a function of the dose. The sample follows a linear response respect to the irradiation dose despite the irradiation temperature. Although the behaviour is linear in all cases, it can be observed that at di7erent temperatures, the slopes of the straight lines increased with temperature, it is perhaps due to the increment of the mobility of the species. From this
T. Mart nez et al. / Radiation Measurements 38 (2004) 455 – 458
457
4..0
O.D
3.0
2.0
1.0
0.0 0
20
40
60
80
min
Bgure, is also evident that even if it is assumed that the primary e7ects of radiation on ice are similar to those produced in the liquid, the rigid structure of the solid modiBed this behaviour, especially in the e7ect of the constant rates of the chemical reactions and the di7usion of the species involved. Therefore, the eLciency for the decomposition of frozen aqueous solution is considerably lower. It falls drastically as the temperature during irradiation was made lower. The di7erence in response is more than one order of magnitude. For this icy iron salts dosimeters at high doses the response is a little bit deviated from the linear behaviour. These results suggest that for this dosimeter the e7ect of temperature in the chemical response result to be very important. 3.2. Solid-state ferrous sulphate The solid sample seems ideal for high-dose dosimetry. Fig. 2 presents a typical M=ossbauer, spectra of a sample irradiated at 3 and 10 MGy. In Figs. 2B and C the peaks of ferrous ions, (outer peaks), are mixed with the peak, (inner peak), corresponding to the ferric ions formed by the irradiation. Standard M=ossbauer spectra of ferric and ferrous iron sulphate (Fig. 2A) were measured before evaluating the spectra of the irradiated sample. The area under each peak was evaluated using the MOSSFIT computer program. These areas gave us the change of the valence state of the iron II into iron III. Fig. 3 shows the dose–response curve. The response obtained for this system was linear up to 10 MGy. This behaviour makes that solid-state ferrous sulphate a good dosimeter system for long irradiations.
Fig. 2. M=ossbauer spectra for a solid-state sample of ferrous sulphate irradiated at (A) 0 MGy (B) 3 MGy and (C) 10 MGy.
PERCENT OF Fe (III)
Fig. 1. Dose response curve for iron (III) at di7erent irradiation temperatures. , 298 K, , 198 K and 4, 77 K. The symbols correspond to the experimental values and the lines are the Btting with the model used.
80 60 40 20 0 0
5 DOSES, MGy
10
Fig. 3. Dose response curve for iron (III) formation obtained by M=ossbauer spectroscopy.
4. Remarks We irradiated frozen solutions of iron salts to evaluate their potential use as dosimeters. The change in valence of iron (II) as a function of dose was linear for frozen solutions. This allows us to conclude that they can be used as a low-temperature dosimeter, up to 600 Gy. In all studied samples, the response change was a function of the irradiation temperature. The latter was observed as a variation of the slope of the curves of dose vs. response. This suggests that a temperature correction should be considered when performing low-temperature irradiation. On the other hand, the simple theoretical model developed agreed with the experimental values fairly well. The iron salts in solid state showed a very wide range in which the response is linear for high radiation doses, ferrous sulphate in solid state presents an excellent way of measuring the energy deposited by the radiation into the
458
T. Mart nez et al. / Radiation Measurements 38 (2004) 455 – 458
sample. Other advantages found were: it is easy to handle, reproducible, and stable in ambient conditions. The evaluation of the response can be made by M=ossbauer spectroscopy. A disadvantage of this system could be that this technique is not easily available in common laboratories. Acknowledgements This work was partially supported by a grant IN115501-3. We thank to Fis. Francisco Garcia and Mr. Salvador Ham for their technical assistance.
References Draganic, I.G., Draganic, Z.D., 1971. The Radiation Chemistry of Water. Academic Press, New York. Martinez, T., 1989. Dosimetro gamma para altas dosis por efecto M=ossbauer. Master Thesis, Facultad de Qu"#mica, UNAM. Negron-Mendoza, A., Albarran, G., Ramos-Bernal, S., Chacon, E., 1994. Some aspects of laboratory cometary models. J. Biol. Phys. 20, 71. Ramos-Bernal, S., Negr"on-Mendoza, A., Cruz-Zaragoza, E., 2000. On the reproducibility of the glow curve of single crystal and commercial LiF. Radiat. Phys. Chem. 57, 735–738.
Radiation Measurements 38 (2004) 455 – 458 www.elsevier.com/locate/radmeas
Dependence of irradiation temperature in the response of iron salts T. Mart"#neza , J. Lartiguea , D. Friasb , G. Sanchez-Mejoradac , A. Negr"on-Mendozad , S. Ramos-Bernald;∗ a Facultad
de Qu mica, UNAM, Ciudad Universitaria, C.P. 04510, M exico DF, Mexico de Ciencias Exatas e Tecnologicas, Universidad Estadual de Santa Cruz, Brazil c Facultad de Medicina, UNAM, Ciudad Universitaria, C.P. 04510, M
exico DF, Mexico d Instituto de Ciencias Nucleares, UNAM, A.P. 70-543, C.P. 04510, M
exico DF, Mexico
b Departamento
Received 15 November 2003; received in revised form 15 November 2003; accepted 25 January 2004
Abstract A potential dosimeter based on aqueous frozen solutions and solid-state salt are presented for the evaluation of the energy transferred during the interaction of high-energy radiation with matter at low temperature. The foundation of these dosimeters, both the solid state and the frozen solutions, is based on the measurement of the change of the iron oxidation state. The systems were irradiated with gamma radiation at di7erent doses (up to 10 MGy), and at di7erent temperatures (from 77 to 298 K). The irradiated samples were analysed by UV-spectroscopy and M=ossbauer spectroscopy. A theoretical model was developed for the chemical reactions system. This model reproduces the experimental e7ects produced by the irradiation in aqueous solutions of ferrous salt. The results showed that the response of the dosimeters depends on the irradiation temperature. At low-radiation doses, the response was linear. In particular, this work can be applied to low-temperature dosimetry can be specially applied to simulation experiments of extraterrestrial bodies, as well as in general to space research. c 2004 Published by Elsevier Ltd. Keywords: Temperature; Irradiation; Iron salts; Dosimetry
1. Introduction Energy is deposited in matter during its interaction with ionizing radiation. In general, the quantiBcation of this transferred energy is very important (Ramos-Bernal et al., 2000). This is specially the case when high-energy radiation interacts with living matter. These interactions are for example in personal dosimetry, incursion of humans into the radiation Beld of the outer space, and in the irradiation of living material. One important assumption for the evaluation of the energy deposited into the sample is that the dosimeter bears as much as possible the same conditions of the sample. Therefore for the cases mentioned above, it is ∗ Corresponding author. Tel.: +52-555-622-4672; fax: +52-5556-162-233. E-mail address: [email protected] (S. Ramos-Bernal).
c 2004 Published by Elsevier Ltd. 1350-4487/$ - see front matter doi:10.1016/j.radmeas.2004.01.034
necessary to perform low-temperature dosimetry. These types of measurements are relevant for laboratory simulation experiments related to some extraterrestrial conditions; say icy bodies, (Negron-Mendoza et al., 1994). In these experiments it is necessary to have a quantitative picture of the energy deposited into dosimeter at the same temperature of the icy body sample (Negron-Mendoza et al., 1994). On the other hand, aqueous solutions are important for dosimetry purposes due to the substantial amount of water in the human body. It is possible to extend the experience about the irradiation of liquids to the frozen solutions (Draganic and Draganic, 1971). However, di7usion of the reactive species, viscosity, and other properties make in general, frozen solutions more complex objects to study. The aim of the present work is (1) to study the irradiation of ferrous sulphate in solid state, and in frozen solutions. (2) To evaluate their behaviour below room temperature, and (3) to Bgure out its potential use as dosimetric systems
456
T. Mart nez et al. / Radiation Measurements 38 (2004) 455 – 458
for low-temperature irradiation. These systems were chosen because they are easy to prepare, as well as for their high sensitivity and stability. Their response is linear at room temperature and therefore we can make a comparison with the response at low temperature. Both the theoretical model and the experimental results, will allow us to evaluate the possible use of iron frozen solutions as a dosimeter.
2. Experimental procedures 2.1. Frozen solutions Chemicals and glassware were treated according to the standard procedures used in Radiation Chemistry (Draganic and Draganic, 1971). The water was triple distilled from an alkaline permanganate solution, from an acid solution of dichromate and the last distillation without adding any reagent. For this study, we used Baker reagent grade ferrous sulphate, sulphuric acid and sodium chloride. Solutions: The Iron salt dosimeter system (Fricke dosimeter) was used as described by Draganic and Draganic (1971). Solutions were in Pyrex cell inside of a Dewar Kask Blled with di7erent cooling agents (water, dry ice and liquid nitrogen). Solutions were frozen gradually to avoid that the glass containers break and to have the same type of crystal ice. The samples were irradiated in a 60 Co gamma source. The dose rate was 9:1 Gy=min. The doses were up to 600 Gy. 2.2. Solid-state iron sulphate Solid samples of heptahydrate ferrous sulphate were in closed glass tubes. Two sets were irradiated with doses from 0.5 to 10 MGy and from 0.2 to 1 MGy. 2.3. Analysis Frozen solutions: The samples were melted after irradiation and the temperature was adjusted to 25◦ C prior measurements. The ferric ions were measured spectrometrically at 304 nm. The molar extinction coeLcient for ferric ion was 2197 M−1 cm−1 at 25◦ C. The doses are based on the ferrous sulphate dosimeter at 25◦ C on the assumption of 15.6 ferric ions are formed by 100 eV absorbed in an air saturated solution. Solid samples: The analysis of these samples was carried out by M=ossbauer spectroscopy, using metal iron, ferric sulphate and ferrous sulphate as calibrators. The optimal thickness of the sample was 0:12324 g cm−2 , and the amount of FeSO4 :7H2 O was 0:623 g. The spectra were measured at room temperature. Measuring the areas of the peaks gave the amount of ferric ion in relation to the total amount of ferrous ion present in the sample. A computer program specially developed for the spectrum separation and Btting (MOSS BAS) is described in Martinez (1989).
2.4. The theoretical model The chemical reactions occurring in the aqueous system are also theoretically simulated in this work. This is carried out by presenting the chemical reactions as a set of di7erential equations of the sti7 type that represents the changes that are taking place in the sample. 2.4.1. Translation from reaction equations to di:erential equations The chemical reaction equations are expressed in a nomenclature very similar to that used by chemists. The program contains a translation part that, by analysing the reaction equations, identiBes, stores the names of the reactants, and stores the reaction constants belonging to the reaction equations. Then a two-dimensional matrix is constructed, which contains the information necessary for computing the right-hand side of the di7erential system. Each line in the matrix has n elements containing the address of the reactant Ri for which the derivative is to be computed, the stoichiometric constant njk , and the address for a rate constant kijk , the source term, and addresses for reactants Rj and Rk on the left side of the reaction equation. For each reactant in the reaction, system there is a line with n elements in the matrix. This matrix is used by the subroutine computing the right-hand side of the di7erential equation system and the Jacobian matrix for the system. 2.4.2. Balance equations The accurate solution of the di7erential equation system describing the chemical reactions requires an overall conservation of the mass balance. Two main factors are involved in the conservation of mass namely the reaction mechanism and the integration process. It must be pointed out that the formal stoichiometric balance needs not be the same as an atom-to-atom balance. The program recognizes each species individual letters and numbers. It is unnecessary to check the mass balance continuously, it is suLcient to do that at the start of the integration, i.e. at time t = 0. 3. Results and discussion 3.1. Frozen solutions Fig. 1 shows the response of iron salt in frozen solution irradiated at di7erent doses, and temperatures. The symbols are the experimental values and the lines are the values calculated by the model. The plots represent the change of the valence state of the divalent iron as a function of the dose. The sample follows a linear response respect to the irradiation dose despite the irradiation temperature. Although the behaviour is linear in all cases, it can be observed that at di7erent temperatures, the slopes of the straight lines increased with temperature, it is perhaps due to the increment of the mobility of the species. From this
T. Mart nez et al. / Radiation Measurements 38 (2004) 455 – 458
457
4..0
O.D
3.0
2.0
1.0
0.0 0
20
40
60
80
min
Bgure, is also evident that even if it is assumed that the primary e7ects of radiation on ice are similar to those produced in the liquid, the rigid structure of the solid modiBed this behaviour, especially in the e7ect of the constant rates of the chemical reactions and the di7usion of the species involved. Therefore, the eLciency for the decomposition of frozen aqueous solution is considerably lower. It falls drastically as the temperature during irradiation was made lower. The di7erence in response is more than one order of magnitude. For this icy iron salts dosimeters at high doses the response is a little bit deviated from the linear behaviour. These results suggest that for this dosimeter the e7ect of temperature in the chemical response result to be very important. 3.2. Solid-state ferrous sulphate The solid sample seems ideal for high-dose dosimetry. Fig. 2 presents a typical M=ossbauer, spectra of a sample irradiated at 3 and 10 MGy. In Figs. 2B and C the peaks of ferrous ions, (outer peaks), are mixed with the peak, (inner peak), corresponding to the ferric ions formed by the irradiation. Standard M=ossbauer spectra of ferric and ferrous iron sulphate (Fig. 2A) were measured before evaluating the spectra of the irradiated sample. The area under each peak was evaluated using the MOSSFIT computer program. These areas gave us the change of the valence state of the iron II into iron III. Fig. 3 shows the dose–response curve. The response obtained for this system was linear up to 10 MGy. This behaviour makes that solid-state ferrous sulphate a good dosimeter system for long irradiations.
Fig. 2. M=ossbauer spectra for a solid-state sample of ferrous sulphate irradiated at (A) 0 MGy (B) 3 MGy and (C) 10 MGy.
PERCENT OF Fe (III)
Fig. 1. Dose response curve for iron (III) at di7erent irradiation temperatures. , 298 K, , 198 K and 4, 77 K. The symbols correspond to the experimental values and the lines are the Btting with the model used.
80 60 40 20 0 0
5 DOSES, MGy
10
Fig. 3. Dose response curve for iron (III) formation obtained by M=ossbauer spectroscopy.
4. Remarks We irradiated frozen solutions of iron salts to evaluate their potential use as dosimeters. The change in valence of iron (II) as a function of dose was linear for frozen solutions. This allows us to conclude that they can be used as a low-temperature dosimeter, up to 600 Gy. In all studied samples, the response change was a function of the irradiation temperature. The latter was observed as a variation of the slope of the curves of dose vs. response. This suggests that a temperature correction should be considered when performing low-temperature irradiation. On the other hand, the simple theoretical model developed agreed with the experimental values fairly well. The iron salts in solid state showed a very wide range in which the response is linear for high radiation doses, ferrous sulphate in solid state presents an excellent way of measuring the energy deposited by the radiation into the
458
T. Mart nez et al. / Radiation Measurements 38 (2004) 455 – 458
sample. Other advantages found were: it is easy to handle, reproducible, and stable in ambient conditions. The evaluation of the response can be made by M=ossbauer spectroscopy. A disadvantage of this system could be that this technique is not easily available in common laboratories. Acknowledgements This work was partially supported by a grant IN115501-3. We thank to Fis. Francisco Garcia and Mr. Salvador Ham for their technical assistance.
References Draganic, I.G., Draganic, Z.D., 1971. The Radiation Chemistry of Water. Academic Press, New York. Martinez, T., 1989. Dosimetro gamma para altas dosis por efecto M=ossbauer. Master Thesis, Facultad de Qu"#mica, UNAM. Negron-Mendoza, A., Albarran, G., Ramos-Bernal, S., Chacon, E., 1994. Some aspects of laboratory cometary models. J. Biol. Phys. 20, 71. Ramos-Bernal, S., Negr"on-Mendoza, A., Cruz-Zaragoza, E., 2000. On the reproducibility of the glow curve of single crystal and commercial LiF. Radiat. Phys. Chem. 57, 735–738.