- Email: [email protected]
Dosimetric characterisation of aqueous solution of brilliant green for low-dose food irradiation dosimetry
Radiation Physics and Chemistry 63 (2002) 713–717
Dosimetric characterisation of aqueous solution of brilliant green for low-dose food irradiation dosimetry Hasan M. Khan*, Mohammad Anwer, Zahid S. Chaudhry Radiation Chemistry Laboratory, National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar 25120, Pakistan
Abstract Dosimetric characterisation of aqueous solution of brilliant green has been studied spectrophotometrically for possible applications in low-dose food irradiation dosimetry. Absorption spectra of unirradiated and irradiated solutions were determined which showed two absorption bands with peaks at 427 and 626 nm and a decrease in absorption as the radiation dose is increased. Radiation-induced bleaching of the dye was measured at wavelengths of maximum absorbance (427 and 626 nm) as well as at 550 and 570 nm. At all these wavelengths, the decrease in absorbance of the dosimeter was linear with respect to the absorbed dose from 20 to 120 Gy. However, the upper dose limit was increased to 200 Gy when the negative logarithm of the absorbance ( log A) was plotted versus absorbed dose. The stability of dosimetric solution during post-irradiation storage in dark at room temperature showed that after some initial bleaching within the first 5 h of irradiation the response was stable for about 18 days. The effect of different light and temperature conditions to which a dosimeter may be exposed during commercial irradiation has been discussed. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Food irradiation; Dosimetry; Brilliant green; Aqueous solution
1. Introduction Interest in food irradiation technology for preservation of food and improving hygienic quality of food is increasing worldwide and in some countries commercialisation of food irradiation has already become a reality. This technology can help countries to reduce food loses during post-harvest storage and to control causes of food-born diseases. A reliable dosimetry system is necessary for commercialisation of food irradiation to satisfy regulatory requirements and for quality assurance. Several chemical dosimeters as well as dye or leuco dye solutions have been used for food irradiation dosimetry over a wide range of doses (McLaughlin et al., 1989; El-Assay et al., 1982, 1995; Kovacs et al., *Corresponding author. Tel.: +92-91-921-6766; fax: +9291-921-6671. E-mail address: hmkhan [email protected], [email protected] (H.M. Khan).
1998). These dyes systems have an advantage of being commercially available, relatively inexpensive and the solution can be easily prepared, handled and measured spectophotometrically. We have earlier reported the dosimetric characteristics of some aqueous solutions that can be used for food irradiation dosimetry (Khan and Anwer, 1993, 1995, 1999). In the present paper, we have investigated the dosimetric properties of aqueous solution of brilliant green with possible applications in low-dose food irradiation dosimetry, such as irradiation of onions, potatoes and garlic, which has been authorised in Pakistan with a maximum dose of 0.2 kGy for inhibition of sprouting (ICGFI Clearance Database; http://www.iaea.org/icgfi/).
2. Experimental procedure Brilliant green was purchased from Aldrich Chemical Co. (USA) and was used as received (dye contents 93%).
0969-806X/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 6 4 0 - 5
714
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717
Brilliant green solution was prepared by dissolving 0.0121 g of the compound in 1 l of triply distilled water to make 25 mmol l 1 solution at natural pH (ca. 4.1). The solution was saturated with oxygen by passing oxygen through the solution for about 30 min. The cobalt-60 gamma rays source (Issledovatel, former USSR) of the Nuclear Institute for Food and Agriculture (NIFA), Tarnab, was used for irradiations. To get reliable and reproducible results, all the samples were irradiated at a fixed position in the radiation field. The dose rate at the selected irradiation position was determined using Fricke dosimetry or radiochromic films (Sehested, 1970; McLaughlin et al., 1991). For irradiation of solutions, about 10 ml of solution was taken in a Pyrex glass tube with a ground stopper and the tubes were placed in the radiation field at a fixed position with the help of a stand and irradiated for a predetermined interval of time. For each absorbed dose, at least three samples were irradiated in order to calculate an average value and standard deviation and all irradiations were carried out at room temperature (ca. 251C). Before and after irradiation, the dosimetric solutions were protected from light. Absorbance measurements were made using a Varian DMS-200 UV-VIS spectrophotometer. Radiation-induced absorption changes were determined against an unirradiated solution as blank unless specified.
3. Results and discussion Absorption spectra of unirradiated as well as irradiated solutions were recorded in the range of 350– 750 nm using distilled water as blank. The absorption spectra of brilliant green solution at pH 4.1 recorded for a range of absorbed doses (20–200 Gy) of gamma rays is shown in Fig. 1. The spectra of the unirradiated solution showed two absorption peaks at 427 and 626 nm which are comparable to the reported values of 428 and 625 nm (Aldrich, 1992–1993). The spectra also showed that there is bleaching of dye around both the regions of maximum wavelengths as the absorbed dose is increased. Therefore, wavelengths of maximum absorption (i.e. 427 and 626 nm) should be suitable wavelengths for dosimetric characterisation; however, in the present study measurements have been made at these peak wavelengths as well as at 550 and 590 nm. 3.1. Response curves and useful dose range The absorbance of the 25 mmol l 1 aqueous brilliant green solution was plotted against absorbed dose and showed linearity with the absorbed dose up to 120 Gy at all the wavelengths and then some deviation from linearity was observed. However, if negative logarithm of the absorbance ( log A) is plotted versus absorbed
Fig. 1. Absorption spectra of 25 mmol l 1 aqueous solution of brilliant green versus water. Top to bottom: unirradiated, 50, 80, 100, 120, 160 and 200 Gy.
dose, a linear response was observed up to 200 Gy as shown in Fig. 2 for all four wavelengths. Therefore, the dosimetric solution can be used in the dose range of 20– 200 Gy. This low-dose range covered by the brilliant green solution is useful for dosimetric applications in the inhibition of sprouting in vegetables, such as onion, potatoes and garlic. Environmental conditions, such as pre-irradiation and post-irradiation storage temperature and light conditions, may affect the response of the dosimeter. Therefore, pre-irradiation stability of the stock solution and post-irradiation stability of the response of brilliant green solution at different storage temperatures and under different conditions of light, which a dosimeter may experience under commercial applications, were investigated. 3.2. Pre-irradiation shelf life Aqueous solutions of brilliant green (25 mmol l 1 at pH 4.1) were stored at room temperature under different light conditions (dark, white fluorescent light inside the laboratory and direct sunlight). To observe any changes in the absorption due to storage time, the absorption spectra were recorded at different time intervals after the preparation of solution. No spectral changes in the solution were observed for a storage period of about 60 days in dark and up to 40 days under white fluorescent light inside the laboratory. However, the solution was unstable in direct sunlight and significant changes in absorption spectra were observed even after 30 min exposure to direct sunlight. The results suggest that the stock solution of brilliant green at its natural pH (4.1) can be used up to 40 days and for daily experiments
- Log (Absorbance)
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717
1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4
550 nm
715
427 nm
590 nm 626 nm
0
40
80
120
160
200
Absorbed Dose, Gy Fig. 2. Radiation response function (in terms of negative logarithm of absorbance) versus absorbed dose in water for 25 mmol l aqueous solution of brilliant green measured at 427, 550, 590 and 626 nm.
1
For longer storage times, all solutions showed a marked decrease in the response.
3.4. Post-irradiation stability under different light conditions
Fig. 3. Stability of response of aqueous brilliant green solution during post-irradiation storage in dark.
fresh solution preparation is not necessary. However, the solution should not be exposed to direct sunlight. 3.3. Post-irradiation stability The post-irradiation stability of the response was checked at room temperature (ca. 251C) in dark. The dosimetric solutions were irradiated to two absorbed doses of 40 and 100 Gy. The stability of the response was studied for a period of about 40 days at 427, 550, 590 and 626 nm as a function of storage time. The results at two peak wavelengths are shown in Fig. 3 and revealed that after a very slight decrease in absorbance during the first 5 h, the response was almost stable up to 18 days.
The light conditions investigated in the present study were white fluorescent light, diffused sunlight inside the laboratory and direct sunlight. To check the stability of response under white fluorescent light, the dosimetric solutions were irradiated to dose levels of 40 and 100 Gy. After irradiation the dosimeters were exposed to white fluorescent light inside the laboratory and analysed at selected wavelengths after regular interval of time. The results are shown in Fig. 4 and it was observed that the radiation-induced absorbance slightly decreased within the first 5 h, after which the absorbance was stable for 9 days. However, at longer storage times, there was a significant decrease in the response. These results are similar to storage experiments in dark except that the solutions exposed to fluorescence light are stable up to a short interval of time (9 days as compared to 18 days). To investigate the effects of diffused sunlight on the stability of response, the irradiated solutions were exposed to diffused sunlight inside the laboratory. The results showed a stable response up to 12 days for both the absorbed doses at all wavelengths; however, a drastic decrease in response was observed for longer storage times. Similar experiments were conducted where the dosimeter solutions were exposed to direct sunlight. The results showed extreme sensitivity of the solution towards direct sunlight, similar to that observed in several other dosimetry solutions, such as ferrous cupric
716
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717
the irradiated solution cannot be measured after irradiation, the irradiated solution should be stored at lower temperatures.
4. Conclusions
Fig. 4. Stability of response of aqueous brilliant green solution during post-irradiation storage in room fluorescence light.
sulphate, coumarin, congo red and triphenyl methane solutions (Khan and Anwer, 1993, 1995, 1999; El-Assay et al., 1995). During this exposure time, the atmospheric temperature was not controlled and the atmospheric temperature at some stages raised up to about 421C. This higher temperature can also affect the response of the dosimeter as discussed below. The foregoing results suggest that the exposure of dosimeter to direct sunlight should be avoided. The other two light conditions (white fluorescent light and diffused sunlight) showed results similar to those observed for storage in dark. However, the irradiated solution is more stable in dark (18 days) as compared to storage in fluorescence light (9 days) or in diffused sunlight inside the laboratory (12 days). 3.5. Effect of temperature on post-irradiation stability The effects of low- and high-storage temperatures (71C and 401C) on the stability of the response of brilliant green dosimeter after irradiation were also checked. Prior to spectrophotometric analysis the solutions were brought to room temperature. Measurements of absorbance were made at different wavelengths (427, 550, 590 and 626 nm). The results showed that at 71C the radiation-induced absorbance decreased for the first 12 h, afterwards the dosimetric response was stable up to 40 days. However, at a longer storage period the response decreased significantly. The effect of postirradiation storage at 401C showed that the dosimetric response was stable up to only 8 days followed by a decrease in response at all the wavelengths of analysis. The above results suggested that the response of the dosimeter was relatively more stable at lower storage temperature (71C) and the stability period decreased as the storage temperature is increased (251C, 401C). Therefore, if a situation arises where the absorbance of
Dilute aqueous solution of brilliant green can be used for low dose applications in food irradiation (20– 200 Gy), such as inhibition of sprouting in fresh vegetables. The solution before and after irradiation is stable for about 2 weeks at room temperature in dark. The solution is also stable for more than 1 week in room fluorescence light and in diffuse sunlight; however, the solution should be protected from direct sunlight. The solution is relatively more stable at lower storage temperatures. The estimated overall uncertainty for dose assessment over all the dose range of interest is about 75% (at 95% confidence level) at constant temperature. Other errors due to variation of response from one batch of dye to other and due to irradiation temperature have not been determined and calibration of each dosimeter solution under given environmental conditions is recommended.
References Aldrich, 1992–1993. Handbook of Fine Chemicals. Aldrich Chemical Co., Milwaukee, WI, p. 179, 333. El-Assay, N.B., Roushdy, H.M., Rageh, M., McLaughlin, W.L., Levine, H., 1982. g-Ray dosimetry using pararosaniline cyanide in dimethyl sulfoxide solutions. Int. J. Appl. Radiat. Isot. 33, 641–645. El-Assay, N.B., Yun-Dong, C., Walker, M.L., Al-Sheikhly, M., McLaughlin, W.L., 1995. Anionic triphenylmethane dye solutions for low-dose food irradiation dosimetry. Radiat. Phys. Chem. 46, 1189–1197. Khan, H.M., Anwer, M., 1993. Stability of response of the ferrous-cupric sulfate dosimeter at different temperature. J. Radioanal. Nucl. Chem. Lett. 173, 199–206. Khan, H.M., Anwer, M., 1995. Effect of temperature and light on the response of an aqueous coumarin dosimeter. J. Radioanal. Nucl. Chem. Lett. 200, 521–527. Khan, H.M., Anwer, M., 1999. Characterization of aqueous solution of congored for food irradiation dosimetry, Techniques of High-Dose Dosimetry in Industry, Agriculture and Medicine, IAEA, Vienna, IAEA-TECHDOC1070, pp. 45–51. Kovacs, A., Wojnarovits, L., Kuructz, C., Alsheikhly, M., McLaughlin, W.L., 1998. Large scale dosimetry using dilute methylene blue dye in aqueous solution. Radiat. Phys. Chem. 52, 539–542. McLaughlin, W.L., Boyd, A.W., Chadwick, K.H., McDonald, J.C., Miller, A., 1989. Dosimetry for Radiation Processing. Taylor & Francis, London, Chapter 8.
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717 McLaughlin, W.L., Chen, Y., Soares, C.G., Miller, A., Van Dyke, G., Lewis, D.F., 1991. Sensitometry of the response of a new radiochromic film dosimeter to gamma radiation and electron beams. Nucl. Instrum. Methods. A 302, 165–176.
717
Sehested, K., 1970. The Fricke dosimeter. In: Holm, N.W., Berry, R.J. (Eds.), Manual on Radiation Dosimetry. Marcel Dekker, New York, pp. 313–317.
Dosimetric characterisation of aqueous solution of brilliant green for low-dose food irradiation dosimetry Hasan M. Khan*, Mohammad Anwer, Zahid S. Chaudhry Radiation Chemistry Laboratory, National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar 25120, Pakistan
Abstract Dosimetric characterisation of aqueous solution of brilliant green has been studied spectrophotometrically for possible applications in low-dose food irradiation dosimetry. Absorption spectra of unirradiated and irradiated solutions were determined which showed two absorption bands with peaks at 427 and 626 nm and a decrease in absorption as the radiation dose is increased. Radiation-induced bleaching of the dye was measured at wavelengths of maximum absorbance (427 and 626 nm) as well as at 550 and 570 nm. At all these wavelengths, the decrease in absorbance of the dosimeter was linear with respect to the absorbed dose from 20 to 120 Gy. However, the upper dose limit was increased to 200 Gy when the negative logarithm of the absorbance ( log A) was plotted versus absorbed dose. The stability of dosimetric solution during post-irradiation storage in dark at room temperature showed that after some initial bleaching within the first 5 h of irradiation the response was stable for about 18 days. The effect of different light and temperature conditions to which a dosimeter may be exposed during commercial irradiation has been discussed. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Food irradiation; Dosimetry; Brilliant green; Aqueous solution
1. Introduction Interest in food irradiation technology for preservation of food and improving hygienic quality of food is increasing worldwide and in some countries commercialisation of food irradiation has already become a reality. This technology can help countries to reduce food loses during post-harvest storage and to control causes of food-born diseases. A reliable dosimetry system is necessary for commercialisation of food irradiation to satisfy regulatory requirements and for quality assurance. Several chemical dosimeters as well as dye or leuco dye solutions have been used for food irradiation dosimetry over a wide range of doses (McLaughlin et al., 1989; El-Assay et al., 1982, 1995; Kovacs et al., *Corresponding author. Tel.: +92-91-921-6766; fax: +9291-921-6671. E-mail address: hmkhan [email protected], [email protected] (H.M. Khan).
1998). These dyes systems have an advantage of being commercially available, relatively inexpensive and the solution can be easily prepared, handled and measured spectophotometrically. We have earlier reported the dosimetric characteristics of some aqueous solutions that can be used for food irradiation dosimetry (Khan and Anwer, 1993, 1995, 1999). In the present paper, we have investigated the dosimetric properties of aqueous solution of brilliant green with possible applications in low-dose food irradiation dosimetry, such as irradiation of onions, potatoes and garlic, which has been authorised in Pakistan with a maximum dose of 0.2 kGy for inhibition of sprouting (ICGFI Clearance Database; http://www.iaea.org/icgfi/).
2. Experimental procedure Brilliant green was purchased from Aldrich Chemical Co. (USA) and was used as received (dye contents 93%).
0969-806X/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 6 X ( 0 1 ) 0 0 6 4 0 - 5
714
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717
Brilliant green solution was prepared by dissolving 0.0121 g of the compound in 1 l of triply distilled water to make 25 mmol l 1 solution at natural pH (ca. 4.1). The solution was saturated with oxygen by passing oxygen through the solution for about 30 min. The cobalt-60 gamma rays source (Issledovatel, former USSR) of the Nuclear Institute for Food and Agriculture (NIFA), Tarnab, was used for irradiations. To get reliable and reproducible results, all the samples were irradiated at a fixed position in the radiation field. The dose rate at the selected irradiation position was determined using Fricke dosimetry or radiochromic films (Sehested, 1970; McLaughlin et al., 1991). For irradiation of solutions, about 10 ml of solution was taken in a Pyrex glass tube with a ground stopper and the tubes were placed in the radiation field at a fixed position with the help of a stand and irradiated for a predetermined interval of time. For each absorbed dose, at least three samples were irradiated in order to calculate an average value and standard deviation and all irradiations were carried out at room temperature (ca. 251C). Before and after irradiation, the dosimetric solutions were protected from light. Absorbance measurements were made using a Varian DMS-200 UV-VIS spectrophotometer. Radiation-induced absorption changes were determined against an unirradiated solution as blank unless specified.
3. Results and discussion Absorption spectra of unirradiated as well as irradiated solutions were recorded in the range of 350– 750 nm using distilled water as blank. The absorption spectra of brilliant green solution at pH 4.1 recorded for a range of absorbed doses (20–200 Gy) of gamma rays is shown in Fig. 1. The spectra of the unirradiated solution showed two absorption peaks at 427 and 626 nm which are comparable to the reported values of 428 and 625 nm (Aldrich, 1992–1993). The spectra also showed that there is bleaching of dye around both the regions of maximum wavelengths as the absorbed dose is increased. Therefore, wavelengths of maximum absorption (i.e. 427 and 626 nm) should be suitable wavelengths for dosimetric characterisation; however, in the present study measurements have been made at these peak wavelengths as well as at 550 and 590 nm. 3.1. Response curves and useful dose range The absorbance of the 25 mmol l 1 aqueous brilliant green solution was plotted against absorbed dose and showed linearity with the absorbed dose up to 120 Gy at all the wavelengths and then some deviation from linearity was observed. However, if negative logarithm of the absorbance ( log A) is plotted versus absorbed
Fig. 1. Absorption spectra of 25 mmol l 1 aqueous solution of brilliant green versus water. Top to bottom: unirradiated, 50, 80, 100, 120, 160 and 200 Gy.
dose, a linear response was observed up to 200 Gy as shown in Fig. 2 for all four wavelengths. Therefore, the dosimetric solution can be used in the dose range of 20– 200 Gy. This low-dose range covered by the brilliant green solution is useful for dosimetric applications in the inhibition of sprouting in vegetables, such as onion, potatoes and garlic. Environmental conditions, such as pre-irradiation and post-irradiation storage temperature and light conditions, may affect the response of the dosimeter. Therefore, pre-irradiation stability of the stock solution and post-irradiation stability of the response of brilliant green solution at different storage temperatures and under different conditions of light, which a dosimeter may experience under commercial applications, were investigated. 3.2. Pre-irradiation shelf life Aqueous solutions of brilliant green (25 mmol l 1 at pH 4.1) were stored at room temperature under different light conditions (dark, white fluorescent light inside the laboratory and direct sunlight). To observe any changes in the absorption due to storage time, the absorption spectra were recorded at different time intervals after the preparation of solution. No spectral changes in the solution were observed for a storage period of about 60 days in dark and up to 40 days under white fluorescent light inside the laboratory. However, the solution was unstable in direct sunlight and significant changes in absorption spectra were observed even after 30 min exposure to direct sunlight. The results suggest that the stock solution of brilliant green at its natural pH (4.1) can be used up to 40 days and for daily experiments
- Log (Absorbance)
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717
1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4
550 nm
715
427 nm
590 nm 626 nm
0
40
80
120
160
200
Absorbed Dose, Gy Fig. 2. Radiation response function (in terms of negative logarithm of absorbance) versus absorbed dose in water for 25 mmol l aqueous solution of brilliant green measured at 427, 550, 590 and 626 nm.
1
For longer storage times, all solutions showed a marked decrease in the response.
3.4. Post-irradiation stability under different light conditions
Fig. 3. Stability of response of aqueous brilliant green solution during post-irradiation storage in dark.
fresh solution preparation is not necessary. However, the solution should not be exposed to direct sunlight. 3.3. Post-irradiation stability The post-irradiation stability of the response was checked at room temperature (ca. 251C) in dark. The dosimetric solutions were irradiated to two absorbed doses of 40 and 100 Gy. The stability of the response was studied for a period of about 40 days at 427, 550, 590 and 626 nm as a function of storage time. The results at two peak wavelengths are shown in Fig. 3 and revealed that after a very slight decrease in absorbance during the first 5 h, the response was almost stable up to 18 days.
The light conditions investigated in the present study were white fluorescent light, diffused sunlight inside the laboratory and direct sunlight. To check the stability of response under white fluorescent light, the dosimetric solutions were irradiated to dose levels of 40 and 100 Gy. After irradiation the dosimeters were exposed to white fluorescent light inside the laboratory and analysed at selected wavelengths after regular interval of time. The results are shown in Fig. 4 and it was observed that the radiation-induced absorbance slightly decreased within the first 5 h, after which the absorbance was stable for 9 days. However, at longer storage times, there was a significant decrease in the response. These results are similar to storage experiments in dark except that the solutions exposed to fluorescence light are stable up to a short interval of time (9 days as compared to 18 days). To investigate the effects of diffused sunlight on the stability of response, the irradiated solutions were exposed to diffused sunlight inside the laboratory. The results showed a stable response up to 12 days for both the absorbed doses at all wavelengths; however, a drastic decrease in response was observed for longer storage times. Similar experiments were conducted where the dosimeter solutions were exposed to direct sunlight. The results showed extreme sensitivity of the solution towards direct sunlight, similar to that observed in several other dosimetry solutions, such as ferrous cupric
716
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717
the irradiated solution cannot be measured after irradiation, the irradiated solution should be stored at lower temperatures.
4. Conclusions
Fig. 4. Stability of response of aqueous brilliant green solution during post-irradiation storage in room fluorescence light.
sulphate, coumarin, congo red and triphenyl methane solutions (Khan and Anwer, 1993, 1995, 1999; El-Assay et al., 1995). During this exposure time, the atmospheric temperature was not controlled and the atmospheric temperature at some stages raised up to about 421C. This higher temperature can also affect the response of the dosimeter as discussed below. The foregoing results suggest that the exposure of dosimeter to direct sunlight should be avoided. The other two light conditions (white fluorescent light and diffused sunlight) showed results similar to those observed for storage in dark. However, the irradiated solution is more stable in dark (18 days) as compared to storage in fluorescence light (9 days) or in diffused sunlight inside the laboratory (12 days). 3.5. Effect of temperature on post-irradiation stability The effects of low- and high-storage temperatures (71C and 401C) on the stability of the response of brilliant green dosimeter after irradiation were also checked. Prior to spectrophotometric analysis the solutions were brought to room temperature. Measurements of absorbance were made at different wavelengths (427, 550, 590 and 626 nm). The results showed that at 71C the radiation-induced absorbance decreased for the first 12 h, afterwards the dosimetric response was stable up to 40 days. However, at a longer storage period the response decreased significantly. The effect of postirradiation storage at 401C showed that the dosimetric response was stable up to only 8 days followed by a decrease in response at all the wavelengths of analysis. The above results suggested that the response of the dosimeter was relatively more stable at lower storage temperature (71C) and the stability period decreased as the storage temperature is increased (251C, 401C). Therefore, if a situation arises where the absorbance of
Dilute aqueous solution of brilliant green can be used for low dose applications in food irradiation (20– 200 Gy), such as inhibition of sprouting in fresh vegetables. The solution before and after irradiation is stable for about 2 weeks at room temperature in dark. The solution is also stable for more than 1 week in room fluorescence light and in diffuse sunlight; however, the solution should be protected from direct sunlight. The solution is relatively more stable at lower storage temperatures. The estimated overall uncertainty for dose assessment over all the dose range of interest is about 75% (at 95% confidence level) at constant temperature. Other errors due to variation of response from one batch of dye to other and due to irradiation temperature have not been determined and calibration of each dosimeter solution under given environmental conditions is recommended.
References Aldrich, 1992–1993. Handbook of Fine Chemicals. Aldrich Chemical Co., Milwaukee, WI, p. 179, 333. El-Assay, N.B., Roushdy, H.M., Rageh, M., McLaughlin, W.L., Levine, H., 1982. g-Ray dosimetry using pararosaniline cyanide in dimethyl sulfoxide solutions. Int. J. Appl. Radiat. Isot. 33, 641–645. El-Assay, N.B., Yun-Dong, C., Walker, M.L., Al-Sheikhly, M., McLaughlin, W.L., 1995. Anionic triphenylmethane dye solutions for low-dose food irradiation dosimetry. Radiat. Phys. Chem. 46, 1189–1197. Khan, H.M., Anwer, M., 1993. Stability of response of the ferrous-cupric sulfate dosimeter at different temperature. J. Radioanal. Nucl. Chem. Lett. 173, 199–206. Khan, H.M., Anwer, M., 1995. Effect of temperature and light on the response of an aqueous coumarin dosimeter. J. Radioanal. Nucl. Chem. Lett. 200, 521–527. Khan, H.M., Anwer, M., 1999. Characterization of aqueous solution of congored for food irradiation dosimetry, Techniques of High-Dose Dosimetry in Industry, Agriculture and Medicine, IAEA, Vienna, IAEA-TECHDOC1070, pp. 45–51. Kovacs, A., Wojnarovits, L., Kuructz, C., Alsheikhly, M., McLaughlin, W.L., 1998. Large scale dosimetry using dilute methylene blue dye in aqueous solution. Radiat. Phys. Chem. 52, 539–542. McLaughlin, W.L., Boyd, A.W., Chadwick, K.H., McDonald, J.C., Miller, A., 1989. Dosimetry for Radiation Processing. Taylor & Francis, London, Chapter 8.
H.M. Khan et al. / Radiation Physics and Chemistry 63 (2002) 713–717 McLaughlin, W.L., Chen, Y., Soares, C.G., Miller, A., Van Dyke, G., Lewis, D.F., 1991. Sensitometry of the response of a new radiochromic film dosimeter to gamma radiation and electron beams. Nucl. Instrum. Methods. A 302, 165–176.
717
Sehested, K., 1970. The Fricke dosimeter. In: Holm, N.W., Berry, R.J. (Eds.), Manual on Radiation Dosimetry. Marcel Dekker, New York, pp. 313–317.