DSpace at VNU: Dose response of polyvinyl alcohol films dyed by methyl red under gamma irradiation

Int J Low Radiation, Vol 6, No 3, 2009 Dose response of polyvinyl alcohol films dyed by methyl red under gamma irradiation Nguyen Trieu Tu and Nguyen Van Dung College of Sciences Hanoi National University 334 Nguyen Trai Road Hanoi, Vietnam E-mail: nguyentrieutu@yahoo.com E-mail: nvdung@yahoo.com Tran Dai Nghiep* Institute for Nuclear Science and Techniques P.O Box 5T-160, Hoang Quoc Viet Road Hanoi, Vietnam E-mail: tdnghiep@vaec.gov.vn *Corresponding author Abstract: Polyvinyl Alcohol (PVA) films containing Methyl Red (MR) were prepared by the cast drying of an aqueous solution of the constituents Irradiation was performed in air at room temperature with 60Co gamma rays at a dose rate of 0.9 kGy/h The characteristics of the films were analysed by a spectrophotometer and densitometer The dose response of the films was described by the energy transfer model The sensitivity of the films was determined The film is recommended for use in gamma dosimetry, gamma radiation protection and accident analysis Keywords: dose response; PVA film; absorbance; optical density; radiation protection; energy transfer model Reference to this paper should be made as follows: Tu, N.T., Dung, N.V and Nghiep, T.D (2009) ‘Dose response of polyvinyl alcohol films dyed by methyl red under gamma irradiation’, Int J Low Radiation, Vol 6, No 3, pp.177–184 Biographical notes: Nguyen Trieu Tu, who died recently, was a Professor at the College of Sciences, Hanoi National University, Vietnam His main interests were in the interaction of radiation with matter, radiation measurement and radiation protection He had published many scientific papers and some books Nguyen Van Dung is an MSc in Physics at the College of Sciences, Hanoi National University, Vietnam His research interest is in applied nuclear physics Tran Dai Nghiep is a Researcher and Lecturer of Nuclear Physics at the Institute for Nuclear Science and Techniques and Hanoi National University, Vietnam His research interests focus on the modern aspects of nuclear physics and the methods applied in nuclear and related sciences Copyright © 2009 Inderscience Enterprises Ltd 177 178 N.T Tu, N.V Dung and T.D Nghiep Introduction Polyvinyl Alcohol (PVA) is an excellent matrix for radiochromic centres and widely used for low- and high-dose dosimetry purposes (Lavrentovich et al., 1965; Chung and Kojima, 1994) An important feature of plastic dosimeters (including PVA film) is their dose response, which is often expressed as a set of exposure calibration factors at different absorbed energies (McLaughlin et al., 1979; Ueno, 1988) The range of linear dose response was preferable to using for PVA dosimeters A desirable characteristic of some dosimeters with a minimal variation in sensitivity over a wide range of doses was given by Poisson statistics (Katz et al., 1972) It was shown that the dose response of any dosimeter could be described by the energy transfer model (Nghiep and Kojima, 1996; Nghiep and Anh, 2006; Nghiep et al., 2006) The energy transfer model was tested for clear and dyed PVA films at a specific wavelength in gamma irradiation (Nghiep et al., 1997; Nghiep, 1998) In this work, the model was tested with optical densities for PVA-Methyl Red (MR) film, in a wide range of doses under gamma irradiation Energy transfer model and dose response of the films According to the energy transfer model, an interested dosimeter is considered a collectively acting aggregate of numerous identical sensitive elements that are uniformly distributed in the dosimeter Gamma irradiation leads to the formation of activated elements from the sensitive ones The correlation between the number of activated elements n(D) at absorbed dose D, dose rate D' and the number of radiation-sensitive elements C can be written as follows: ⎡ D ⎞⎤ D⎞ ⎛ ⎛ n(D) = n s ⎢1 − exp ⎜ − k ⎟ ⎥ + n exp ⎜ − k ⎟ , D′ ⎠ ⎦ D′ ⎠ ⎝ ⎝ ⎣ (1) and ns = pC , p−q (2) where: k0 = the probability that one sensitive element will be activated and detectable per unit of time in the irradiation process ns and n0 = the numbers of activated elements at D = ∞ and D = 0, respectively p and q = the probabilities that one sensitive element will be activated and reactivated per unit of time, respectively Experiment PVA (–CH2CHOH–)1500 was dissolved in ionised water Added to the mixture was 0.005 g of MR, (CH3)2NC6H4N:NC6H4COOH, heated and stirred at 80°C for 30 to make a homogeneous solution containing 1.5% PVA by weight The resulting mixture was poured onto a flat glass plate to form a film about 20 µm thick by naturally drying at room temperature Dose response of PVA films dyed by methyl red under gamma irradiation 179 Films of three pieces with dimensions of 40 × 10 mm were prepared and put in polyethylene pouches for irradiation and obtaining the average value of absorbances The dyed PVA films were irradiated under gamma rays of 60Co source of the irradiation centre Irradiation was carried out at doses from to 140 kGy with a dose rate of 0.9 kGy h–1 The electron equilibrium was achieved by using polymethyl methacrylate (PMMA) sandwiched slabs The absorbances (Abs) A0 and A of the films before and after irradiation, respectively, were measured at wavelength 480 nm by spectrophotometer UV-VIS JASCO-V-350 (JASCO, Japan) with a wavelength accuracy ±0.2 nm The film densities (OD) were also measured by the densitometer X-Rite Model 301 A ratio of specific absorbances per thickness unit AR is used for the correction of film thickness variation, as follows: A A AR = t = , A0 A0 t (3) where t is the thickness of the film The ratio of absorbances (Equation 3) is not dependent on film thickness t It was shown that, to a first-order approximation, the relative film absorbance AR and relative film optical density (OD)R are proportional to the number of activated elements n(D), as follows: A(D) = α n(D), (4) (OD) = β n(D) (5) where α and β are proportional coefficients In our case, an activated element implies a unit of the optical density per unit of film thickness Consequently, the correlation between (OD)R and D could be described by Equation (1) The sensitivity of the film is defined as follows: k= k0 D′ (6) Results and discussion The specific absorption spectra with a specific absorbance (Abs) at 425 nm for the PVA film dyed by MR before and after gamma irradiation are introduced in Figures and Note that the initial form of spectra with a specific wavelength at 425 nm is strongly changed at high doses and broaden to the side of large wavelengths with a new specific peak at 485 nm (Figures 3–6) 180 N.T Tu, N.V Dung and T.D Nghiep Figure The absorption spectrum of PVA-MR film before irradiation with a specific wavelength at 425 nm (see online version for colours) Figure The absorption spectrum of PVA-MR under 60Co gamma-ray irradiation at D = 50 kGy (see online version for colours) Dose response of PVA films dyed by methyl red under gamma irradiation Figure The absorption spectrum of PVA-MR film at D = 100 kGy (see online version for colours) Figure The absorption spectrum of PVA-MR film at D = 120 kGy (see online version for colours) 181 182 N.T Tu, N.V Dung and T.D Nghiep Figure The absorption spectra of PVA-MR film at D = 120 kGy (1) and D = 140 kGy (2) (see online version for colours) Figure The absorption spectra of PVA-MR film at D = 100 kGy (1), 120 kGy (2), 130 kGy (3) and 140 kGy (4) (see online version for colours) The correlation between absorbed doses and optical densities measured in relative units with average error of 5% by the densitometer X-Rite Model 301, is introduced in Figure The solid line was described by Equations (1) and (5) with the following coefficients: (OD)Rs = 4.35 ± 1.87 (OD)R0 = 1.028 ± 0.031 k = 0.0027 ± 0.0018 R2 = 0.9856 The value of the correlation coefficient R2 shows a good agreement between the experimental data and theoretical descriptions Dose response of PVA films dyed by methyl red under gamma irradiation Figure Note: 183 The dose response of the PVA-MR film The solid line is described by Equation (1) Conclusions The dose response of PVA-MR films was investigated in a wide range of absorbed doses for gamma rays The correlation between the optical densities and the absorbed dose was described by the energy transfer model The film is recommended in use for gamma dosimetry, gamma radiation protection and accident analysis References Chung, W.H and Kojima, T (1994) ‘Application of dyed PVA films to 150–300 keV electron beam dosimetry’, Radioisotopes, Vol 43, No 5, pp.16–20 Katz, R., Sharma, S.C and Homayoofar, M (1972) ‘The structure of particle track’, in F.H Attix (Ed.) Topics in Irradiation Dosimetry, Supplement No 1, Academic Press Lavrentovich, Y.I., Levon, A.I., Mel’nikova, G.N and Kabakchi, A.M (1965) ‘Gamma and neutron dosimetry in nuclear reactors by means of colored polyvinyl alcohol films’, Soviet Atomic Energy, Vol 19, pp.1189–1192 McLaughlin, W.L., Humphreys, J.C., Radak, B.B., Miller, A and Olejnik, T.A (1979) ‘The response of plastic dosimeters to gamma rays and electrons at high absorbed dose rates’, Radiation Physics and Chemistry, Vol 14, pp.535–550 Nghiep, T.D (1998) ‘Correlation between low linear energy transfer and interaction characteristics of gamma rays for dyed polyvinyl alcohol’, Communications in Physics, Vol 8, No 4, pp.237–240 184 N.T Tu, N.V Dung and T.D Nghiep Nghiep, T.D and Anh, V.T (2006) ‘Correlation between the radon levels and the lung cancer mortality rates – experimental and theoretical problems’, Int J Low Radiation, Vol 2, Nos 1–2, pp.84–87 Nghiep, T.D and Kojima, T (1996) ‘An energy transfer model for radiation dosimetry’, Communications in Physics, Vol 6, No 2, pp.5–12 Nghiep, T.D., Kojima, T., Tu, N.T and Ha, T.V (1997) ‘Dose-response characteristics of high-sensitive clear Polyvinyl Alcohol (PVA) film’, Communications in Physics, Vol 7, No 1, pp.5–12 Nghiep, T.D., Minh, D.T.N and Minh, L.V (2006) ‘Dose-response of photographic emulsions under gamma irradiation’, Int J Low Radiation, Vol 3, No 1, pp.88–92 Ueno, K (1988) ‘Development of a plastic dosimeter for industrial use with high doses’, Radiation Physics and Chemistry, Vol 31, Nos 4–6, pp.467–472  ... naturally drying at room temperature Dose response of PVA films dyed by methyl red under gamma irradiation 179 Films of three pieces with dimensions of 40 × 10 mm were prepared and put in polyethylene... for irradiation and obtaining the average value of absorbances The dyed PVA films were irradiated under gamma rays of 60Co source of the irradiation centre Irradiation was carried out at doses... value of the correlation coefficient R2 shows a good agreement between the experimental data and theoretical descriptions Dose response of PVA films dyed by methyl red under gamma irradiation