OJPChemOpen Journal of Polymer Chemistry2165-6681Scientific Research Publishing10.4236/ojpchem.2013.31001OJPChem-28468ArticlesChemistry&Materials Science Dosimeter Film Based on Ethyl Violet-Bromophenol Blue Dyed Poly(Vinyl Alcohol) eifEbraheemMousheraEl-Kelany28022013030115November 1, 2012December 2, 2012 December 14, 2012© Copyright 2014 by authors and Scientific Research Publishing Inc. 2014This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

Dyed poly(vinyl alcohol) (PVA) films, prepared by a simple technique of casting aqueous solutions of PVA containing a mixture of Ethyl violet and bromophenol blue (EV-BPB) on a horizontal glass plate, are useful as routine high-dose dosimeter in the 1 - 30 kGy range. The color of films changes from violet to yellow when exposed to gamma radiation. The response of this dosimeter depends up on the concentration of chloral hydrate (CH) in the polymer material. The radiation chemical yield (G-value) of PVA dyed film was calculated and found to increase by increasing concentration of chloral hydrate. Post-irradiation storage on the response of the films are discussed. The overall combined uncertainty (at 2σ) associated with measurement of response (ΔA mm-1) at 600 nm for dose range 1 - 15 kGy is 5.6%.

Ethyl-Violet and Bromo-Phenol Blue; Poly(Vinyl Alcohol); Gamma Ray Dosimeter1. Introduction

Treatment of food by radiation has rendered routine dosimeters and labels in the 1 - 30 kGy range necessary. There are few solid-state dosimeters known to be applicable in this dose range, e.g. amber and Gammachrome perpex [1,2] and analnine dosimeters [3]. Radiation-sensitive indicators may be used to show that products have been exposed to radiation source. A new label dosimetry system based on the idea of mixing more than one dye having different sensitivities to radiation has been developed [4]. Radiation sensitive materials consisting of a chlorine-containing polymer and an acid-sensitive dye are known [5,6]. The chlorine-containing polymer is dehydro-chlorinated when the material is irradiated there by reducing pH and causing the acid-sensitive dye to change color. A similar color can be produced if a halogen-containing substance is present in the dye-containing matrix [7]. Many other films containing a radiation sensitive pH indicator dye with chloral hydrate have been prepared to be used γ-radiation monitoring dosimeters and indicators [8]. Radiation bleachable organic dyes were widely investigated [9], and for monitoring the absorbed dose delivered by electron beams and gamma rays [10]. A radiation dosimeter from acid indicators by coating a high molecular weight polymer support (e.g. polyester film) with a composition containing a halogen-containing polymer (e.g. PVC) developed [11], a pigment which changes color with the changes of pH and basic material (e.g. KOH in EtOH). A chlorine-containing polymer is not necessary for this reaction to occur.

The current work describes the initial investigations of films which combine (PVA), mixture of EV and BPB and chloral hydrate to give dosimeter films.

2. Experimental2.1. Preparation of Stock Dye Solutions of EV and BPB

The stock of the dye was prepared by dissolving 0.08 g of ethyl violet dye (EV) (product of RIEDEL DEHAEN, Germany) in 50 ml distilled water. Also, the stock solution of the sodium salt of the dye was prepared by dissolving 0.08 g of bromo-phenol blue (BPB) (product of CHAMPOL, Czech Republic) in 50 ml distilled water. These two stock solutions were used in the preparation process of the mixed dye dosimetry film.

2.2. Preparation of (EV-BPB)/PVA Mixed Dye Films

10 grams of fully hydrolyzed poly vinyl alcohol (99% - 100%) from J. T. Baker chemicals Co., USA were dissolved in 250 ml doublydistilled water at about 60˚C. The solution was kept well stirred at the same temperature of about 24 h, then left to cool. To this solution 2 mg of (EV-BPB) mixture was added and further stirred for 3 hour so as to obtain a uniformly colored PVA solution. To each 30 ml of the well mixed solution 0.2, 0.5, 0.8 and 1 g of chloral hydrate CH (from Merck Co.) were added. The dyed PVA solution are poured onto a 15 × 15 cm polyester sheet (0.1 mm thickness) fixed on a horizontal leveled glass plate and kept to dry in dark room at temperature (25˚C ± 2˚C). After stripping the films they were stored in dark at relative humidity of 35%. The thicknesses of the films were measured using DigitrixMark II thickness gauge at 5 randomly selected places with a thickness gauge having an accuracy of 0.055 ± 0.002 mm.

3. Instruments

The absorption spectra of unirradiated and irradiated films were measured throughout the wavelength range 200 - 800 nm using a UVIKON 860 spectrophotometer. The film thickness was measured using a Digitrix-Mark II gauge (precision ±1 µm, 1σ). Irradiation was carried out with gamma radiation in the 60Co gamma chamber 4000 A irradiation facility (product of India). The absorbed dose rate in the irradiation facility was measured to be 6.334 kGy/h, using reference Alanine dosimeters. The electronic equilibrium conditions were maintained during irradiation.

4. Results and Discussion4.1. Absorption Spectra

The absorption spectra of (EV-BPB)/PVA films without chloral hydrate recorded before and after irradiation to different doses are shown in Figure 1. The main absorption band in visible region characteristic to violet color peaking at 600 nm. The amplitude of this band, decreases gradually with the increase of dose of γ-ray photon, at λmax 600 nm. The absorption spectra of unirradiated and irradiated films were measured throughout the wavelength range 200 - 800 nm. The absorption spectra of these films with chloral hydrate recorded before and after irradiation to different doses are shown in Figure 2. The ampilitude of this band, decreases gradually with the increase of dose of γ-ray photon. It is clear from the spectra of irradiated film that, the mixed dyes (EV-BPB) degraded by applying of gamma rays on the film. Four different chloral hydrate concentrations 16.6, 41.6, 66.6 and 83.3 phr with 0.3 phr of (EV-BPB) were examined.

The acid sensitive dye in the film changes its color from violet to yellow by irradiation due to consequent lowering of the pH of the film caused by the HCl generated from the radiolysis of chloral hydrate [12].

4.2. Response Curves

For dosimetry, optical density read out was carried out at 600 nm for (EV-BPB)/PVA films for different concentration of chloral hydrate (16.6, 41.6, 66.6 and 83.3 phr). Figure 3 show the response curves in terms of change

optical density per unit thickness ∆A = Ao − Ai where Ao and Ai are values of optical density for the unirradiated and irradiated films, respectively. The curves show that the useful dose range extends up to 30 kGy. It can be noticed that all curves show the same trend where they are linear up to about 15 kGy, then tend to saturate at higher doses. But, all curves differ in the response value (initial curve slope). Figure 4 shows the relation between the response value (initial curve slope) and the concentration of chloral hydrate. It can be seen that, the response increases by increasing the concentration of chloral hydrate.

Figure 5 shows the relation between the dose at saturation (reach saturation more than 95% of indicator changes its color) and the concentration of chloral hydrate. It can be seen that, the dose at saturation decreases with the increase of [CH] from 16.6 up to 83.3 phr. Plotting the concentration of chloral hydrate scale a straight line was obtained which can be expressed as follows:

D = 21.8 − 0.23 [chloral hydrate]

D is the dose at saturation in kGy.

4.3. Calculation of Concentration of Hydrogen Ion

Figure 6 shows the total amount of H+ ion in films containing different concentrations of chloral hydrate as a function of absorbed dose at 600 nm wavelength [13]. It can be seen that the amount of acid formed increases gradually with the increase of absorbed dose. The rate of increment of acid increases with the increase of both absorbed dose and concentration of chloral hydrate.

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