Dosimetric characteristics of a Radiochromic polyvinyl butyral film containing 2,4-hexadiyn-1,6-bis(n-butyl urethane

Dosimetric characteristics of a Radiochromic polyvinyl butyral filmcontaining 2,4-hexadiyn-1,6-bis(n-butyl urethane)

A.A. Abdel-Fattah a, Y.S. Soliman a,n, A.M.M. Bayomi a, A.A. Abdel-Khalek b

a National Center for Radiation Research and Technology (NCRRT), Atomic Energy Authority, P. O. Box 8029, Nasr City, Cairo 11787, Egyptb Faculty of Science, Chemistry Department, Beni-Suef University, Beni-Suef City, Egypt

H I G H L I G H T S

� A new thin film based on 2,4-hexadiyn-1,6-bis(n-butyl urethane) is developed.� The film is suitable for industrial dosimetry in the 3–150 kGy range.� Overall uncertainty of dose measurements does not exceed 6.9% (2s).

a r t i c l e i n f o

Available online 31 December 2013

Keywords:DosimetryRadiochromic filmIndustrial irradiations

a b s t r a c t

A radiation-sensitive compound 2,4-hexadiyn-1,6-bis(n-butyl urethane) (HDDBU) was synthesized,characterized by FTIR spectroscopy, and introduced into a thin polyvinyl butyral film to form a radiationdosimeter for industrial irradiation facilities. The monomer polymerizes under gamma radiation,inducing change in the film spectrum in the range of 200–400 nm. According to XRD spectroscopy,the film contains monomeric HDDBU in a non-crystalline state. The dose response function, radiationsensitivity, and dependences of the response on environmental factors were studied. Uncertainty of dosemeasurements with the proposed dosimetry system was analyzed in detail.

& 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Conjugated diacetylene monomers are radiation-sensitive mate-rials. When irradiated in the crystalline state, they undergo atopochemical polymerization (1,4-addition reaction) to form inten-sely colored fully conjugated polydiacetylenes (Wegner, 1972; Caoand Mallouk, 1991). The color of polydiacetylenes stems from theextensive delocalization of π-electrons along π-conjugated polymerchains. The color intensifies progressively with increasing absorbeddose (Patel, 1979, 1981). Fig. 1 (a–c) shows a diagram of topochemicalpolymerization of diacetylene units into π-conjugated polydiacety-lene under ionizing radiation in the crystalline state (Janzen et al.,2006; Hu and Li, 2002). However, there is also crosslinking in thenon-crystalline state, as shown in Fig. 1 (d and e) (Hu and Li, 2002).

Conjugated diacetylenes have been extensively investigated asdosimetric materials for industrial irradiation processes (Patel,1981, 2009; Soliman et al., 2013). They are commonly used asradiation-sensitive components in Gafchromic film formulations(Butson et al., 2001; Cheung et al., 2005; Vandana et al., 2011).

Generally, conjugated diacetylenes are synthesized by oxidativecoupling of the corresponding acetylenes (Hay, 1962). This method iscommonly used to prepare diacetylene diol compounds from acet-ylenic alcohols, such as propargyl alcohol (Hu and Li, 1999). Diace-tylene diols can undergo an addition reaction to produce highly π-conjugated and highly radiation-sensitive monomers of diacetylenediurethane (Wegner, 1972; Patel, 1981; Shchegolikhin et al., 2003).

A thin solid film with diacetylene polyester of poly(hexa-2,4-diynylene adipate) as a radiation-sensitive component was proposedfor monitoring doses in the range of 0.5–60 kGy (Soliman, 2007).Under gamma rays, this component undergoes crosslinking polymer-ization and changes the color of the solid film from faint yellowish-orange to deep orange. The spectrum of the irradiated film features anabsorption band in the vicinity of 500 nm with a shoulder near465 nm. The expanded uncertainty of dose measurements based onthis phenomenon was reported to be less than 5.6% at the confidencelevel 95%. A conjugate diacetylene-diol monomer of 2,4-hexadiyn-1,6-diol was synthesized by oxidative coupling of propargyl alcohol andincorporated into a thin polyvinyl butyral (PVB) film for dosimetry inthe dose range of 0.5–65 kGy (Abdel-Fattah et al., 2009). The reportedoverall uncertainty of dose measurements at 273 nm was under 5%(2s), provided that the contributions from the temperature andhumidity effects were not included. A conjugated monomer of 10,12-pentacosadiynoic acid (PCDA) undergoes topochemical solid-state

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0969-8043/$ - see front matter & 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.apradiso.2013.12.023

n Corresponding author. Tel./fax: þ2 02 2671 4166.E-mail address: [email protected] (Y.S. Soliman).

Applied Radiation and Isotopes 86 (2014) 21–27

polymerization by the gamma and UV radiations, which makes itpossible to prepare a very thin film using the Langmuir–Blodgetttechnique; the films thus obtained can be used for dosimetry invarious dose ranges (Ali et al., 1996). PCDA was recently added tosolutions of PVB in low (3–10%) (Soliman et al., 2013) and high(20–50%) (Abdel-Fattah et al., 2012) concentrations to manufacturethin film dosimeters. The thin film dosimeters containing PCDA at thelower concentrations were found to be useful for spectrophotometricmeasurements of high doses (3–100 kGy). On the other hand, thedosimeters with the higher PCDA concentrations enable one tomeasure doses in the 15–2500 Gy range using spectral reflectancecolorimetry. Upon gamma-ray exposure, films with the lower PCDAconcentrations remained colorless, while the films with the highermonomer concentrations developed a deep blue color. These resultssuggest that PVB films with PCDA can be used as dosimeters in variousradiation processing technologies, such as sterilization of medicaldevices, food irradiation, insect population control, and blood irradia-tion. Additionally, the films can be used as detectors of irradiatedblood and food (Abdel-Fattah et al., 2012). The spectrum of theunirradiated thin film of lower PCDA amount exhibits four absorptionbands, namely, at 216, 227, 241, and 256 nm (Soliman et al., 2013).Upon gamma-ray exposure, two new bands appear at 271 nm and286 nm, and their intensities grow with the absorbed dose. Theexpanded uncertainty of dose measurements with both the dosi-meters was approximately 6% (2s).

The objective of the present study was to synthesize radiation-sensitive monomer 2,4-hexadiyn-1,6-bis(n-butyl urethane) (HDDBU),to characterize it with FTIR spectroscopy, and to study the dosimetrypotential of PVB films containing this substance. The prepared filmswere characterized by the UV-visible and XRD spectroscopies beforeand after gamma-ray exposure. The radiation sensitivity of thedosimeters was characterized, and the uncertainty of doses mea-sured with them was calculated and discussed.

2. Experimental

2.1. Synthesis of 2,4-hexadiyn-1,6-diol

Conjugated diacetylenes are usually synthesized by oxidativecoupling of acetylenes (Hay, 1962). This monomer was synthesizedby oxidative coupling of propargyl alcohol (99%, Aldrich) in thepresence of cuprous chloride (97%, Nice Chemicals, India) and N,N,N0,N0-tetramethyl ethylenediamine (98%, Fluka) under oxygenbubbling (Shchegolikhin et al., 2003; Abdel-Fattah et al., 2009;Hu and Li, 1999). Fig. 2a shows the reaction of synthesis of 2,4-hexadiyn-1,6-diol. The product was recrystallized from ethylacetate (99.5%, Sigma-Aldrich) and stored in a sealed bottlewrapped in aluminum foil in a desiccator in a cool and dark place.The obtained 2,4-hexadiyn-1,6-diol had pale yellow color; theyield was about 67%; and the melting point was 110–112 1C. Thecompound is highly sensitive to UV light, and it is stronglyrecommended to put it into a dark and cool place immediatelyafter crystallization and drying. A polymeric film with this mono-mer was previously investigated as a dosimeter in the dose rangeof 0.5–65 kGy (Abdel-Fattah et al., 2009).

2.2. Synthesis of 2,4-hexadiyn-1,6-bis(n-butyl urethane (HDDBU)

HDDBU was synthesized by adding freshly-prepared monomer2,4-hexadiyn-1,6-diol to an anhydrous THF (Aldrich) solution ofbutyl isocyanate (98%, Aldrich), di-n-butyltin bis(2-ethylhexano-ate) (Alfa-Aesar) and triethylamine (99%, Merck) (Wegner, 1972;Patel, 2009; Shchegolikhin et al., 2003). Fig. 2b shows the synth-esis of HDDBU. The product was recrystallized from acetone(99.5%, Merck) twice and kept in a dark, cool, and dry place. Itwas faint blue with the melting point at 74–76 1C. Gammarays readily polymerized the monomer, making it deep blue.

Fig. 1. Possible reactions of conjugated diacetylene molecules under ionizing radiation (Hu and Li, 2002). Diacetylene units in a stack in a crystal (a) react via topochemicalsolid-state polymerization to form polydiacetylene chains (b) and (c). By contrast, conjugated diacetylene units in a non-crystalline environment (d) crosslink via randomreactions of C0C triple bonds to form polymer (e).

A.A. Abdel-Fattah et al. / Applied Radiation and Isotopes 86 (2014) 21–2722

The intensity of the color grew with the absorbed dose, in linewith the results by Patel (1981). A FTIR analysis of the monomer(spectrometer ATI Mattson, Genesis Series, Unicam, UK) revealedtwo absorption bands, namely, at 3329 and 1545 cm-1, whichindicated N–H stretching and bending vibrations of a secondaryamine, respectively. In addition, the absorption band of diacety-lenes (C� C, medial alkyne) around 2149 cm�1 was observed. Thespectrum also featured absorption bands in the range 2956–2872 cm�1 (C–H stretching of aliphatic hydrocarbons), a band at1707 cm�1 (C¼O), and another band at 1647 cm�1 (C¼C).

2.3. Preparation of the thin-film dosimeter

Three batches of thin films with different concentrations ofHDDBU in PVB (pioloform BR18, average MW �50–60�103,Wacker Co., USA) were prepared. Three solutions containing 20%PVB along with 5, 10, or 15 phr (parts per a hundred parts of theresin) of HDDBU in a mixture of butanol and acetone (1/2 v/v)were stirred for about 24 h at room temperature in the dark. Thenthe mixtures were put onto polyester sheets (size A4) using anAutomatic Film Applicator System (Braive Instrument, Belgium)adjusted to 250 mm. The coated polymer films thus obtained weredried in a dark place at room temperature for 72 h. Finally, the thinfilms were stripped from the polyester sheets, cut into 1�1 cm2

pieces and stored in a tightly enclosed envelop at 10 1C and normalhumidity. The thickness of the obtained dry films was found to be0.03270.004 mm (1s).

2.4. Radiation source and measurement instruments

The manufactured films were irradiated to 3–150 kGy in aGamma Cell GC-220 Excel, (MDS Nordion, Canada) using aspecially designed polystyrene holder to ensure electron equili-brium. The dose rate to water in the center of the sample holderwas calibrated by the National Physical Laboratory (NPL) in the UKusing the alanine dosimetry system according to the standard ISO/ASTM 51261 (2004). During the period of the study, the dose ratewas approximately �2.50 kGy h�1. The radiation source wasequipped with a temperature control unit manufactured andinstalled in the cavity of the GammaCell by NPL. The temperaturesystem made use of an oven comprising a cross-linked polystyreneshell with aluminum lining. Heating and, to a lesser extent, coolingwere provided by means of a peltier junction mounted in the baseof the oven. Platinum thermistors were used to measure the

temperature of the sample and the temperatures at both sides ofthe peltier junction. The thermistors had been calibrated at NPL,and their calibration was periodically verified during the studyagainst another calibrated thermometer.

The absorption spectra of the film dosimeters irradiated todoses between 3 kGy and 150 kGy were recorded with a UV–visspectrophotometer Evolution 500 (Thermo Electro Corp., UK) inthe range 200–400 nm. The optical density at the wavelength λmax

of the most intense peak was plotted vs. the absorbed dose. Thefilm thicknesses were measured with a Digitrix-Mark II thicknessgauge (precision71 mm).

The x-ray diffraction (XRD) patterns of pure solid HDDBU, purePVB film, and the compound PVB film with HDDBU before andafter irradiation were recorded at room temperature with aShimadzu x-ray diffractometer (Model XRD-6000, 40 kV, 30 mA)equipped with an x-ray tube containing a Cu target. A continuousscanning mode at the scanning speed 8 deg min-1 in the range of4–90o (2θ) was used.

3. Results and discussion

3.1. Effect of gamma rays on the HDDBU/PVB films

Fig. 3 shows absorption spectra of the films irradiated tovarious doses. In this study, we focused only on the radiation-induced changes of the spectrum in the UV range (200–400 nm).The spectrum of unirradiated films featured three absorptionbands at 233, 245, and 259 nm, which are characteristic of thediacetylene chromofore (Soliman et al., 2013; Kühling et al., 1990).These bands grow in intensity with the radiation dose without anyshifts. In addition, two new absorption bands, namely, at 273 and285 nm, which are characteristic of a diacetylene polymer, developupon irradiation, and their intensities increase proportionally tothe absorbed dose. Additionally, the band initially located at273 nm shifts gradually to higher wavelengths as the absorbeddose grows. We selected the 259-nm band to study the doseresponse because its radiation sensitivity was similar to the

Fig. 2. Syntheses of 2,4-hexadiyn-1,6-diol (a) and HDDBU (b).

Fig. 3. Absorption spectra of the PVB films with 10 phr of HDDBU irradiated tovarious doses.

A.A. Abdel-Fattah et al. / Applied Radiation and Isotopes 86 (2014) 21–27 23

sensitivities of the other bands, its position in the spectrum wasstable, and its peak was sharp. Irradiation makes the film faintyellow, in accordance with the absorption band developing around440 nm (inset in Fig. 3).

Pure HDDBU in the solid state polymerizes under gammairradiation topochemically, which makes it blue. However, whenirradiated as a low-concentration additive in the PVB film, like inthis study, it changes its color only to faint yellow (inset in Fig. 3).This can be attributed to a lower probability of formation of long π-conjugated polymer chains in the polymer matrix, a high degree ofconjugation of which would produce the blue color. Also, in thepolymer matrix, the monomer molecules are not in the crystallinestate (Fig. 4), which would enable them to polymerize topochemi-cally, but in the amorphous state, where they can polymerize onlyrandomly (Wegner, 1972; Janzen et al., 2006; Hu and Li, 2002). Thetransformation of the monomer from the crystalline to theamorphous state in the process of the film preparation isevidenced by the very broad diffraction bands of HDDBU in PVB,which overlap with the bands of the matrix. These are differentfrom the sharp diffraction bands of HDDBU in the pure solid state.

3.2. Dose response

Fig. 5 shows dose response functions of the films with variousconcentrations of HDDBU. Each dose point corresponds to fourreplicate films. The dose dependences are linear up to 50 kGy(Fig. 6): the linear correlation coefficients were found to be 0.997,0998, and 0.995 for the films with the HDDBU concentrations of 5,10, and 15 phr, respectively. The sensitivity of the films to radiationdoses, expressed as the slope of the dose response curve, increaseslinearly with the HDDBU concentration (Fig. 7). The film with15 phr of HDDBU is approximately 2.4 times more sensitive thanthe film with 5 phr of HDDBU.

3.3. Effect of the pre-irradiation storage conditionson the dose response

To investigate possible effects of preirradiation storage on themanufactured films, we monitored absorbances of unirradiatedfilms stored under different conditions. Three groups of filmsmanufactured approximately one month before the start of theexperiment were stored under different conditions, and theirabsorbances at 259 nm were monitored for 85 days. One of thegroups was stored at room temperature in the dark; another groupwas stored at room temperature exposed to laboratory fluorescentlight; and yet another group was stored at �4 1C in the dark. Therelative humidity of the air was (4273)% in all the cases. As onecan see from Fig. 8, the absorbances of the films stored in the darkat �4 1C remained essentially unchanged during the whole periodof the observations. The absorbances of the films stored at roomtemperature in the dark changed about 3% over the same period oftime. However, the absorbances of the films stored at roomtemperature under fluorescent light increased approximately 8%by the end of the observation. So, storage of unirradiated films inthe dark at �4 1C is recommended.

Fig. 4. XRD patterns of unirradiated solid pure HDDBU, an unirradiated PVB filmwithout additives, and a PVB film containing HDDBU before and after irradiation.

Fig. 5. Dose response of the HDDBU/PVB films at 259 nm in the full dose range of3–150 kGy. ΔA¼(Ai�Ao) / f, where Ai and Ao are absorbances of the irradiated andunirradiated films, respectively, and f is the film thickness. Error bars represent 2s.

Fig. 6. Dose response of the HDDBU/PVB films at 259 nm in the low-dose range of3–50 kGy. Error bars represent 2s.

A.A. Abdel-Fattah et al. / Applied Radiation and Isotopes 86 (2014) 21–2724

3.4. Effect of the post-irradiation storage conditions on the doseresponse

Multiple HDDBU/PVB films with 10 phr of HDDBU were irra-diated to 25 kGy approximately one month after their manufactur-ing. After the irradiation, they were stored under differentconditions. One group was stored at room temperature in thedark; another group was stored at room temperature underlaboratory fluorescence light; and yet another group was storedat �4 oC in the dark. The relative air humidity was always(4273)%. The absorbances of the films at 259 nm were measuredperiodically over 85 days of storage (Fig. 9). The signals of the filmsstored at �4 1C were very stable over the whole observationperiod. On the contrary, the responses of the films stored at roomtemperature, either in the dark or under fluorescent light,increased rapidly during the first week of storage and then grewmore slowly until the end of the observation period. The responsesof the films stored in the dark grew roughly 1.5%, 9%, and 13%during the first 1, 8, and 24 days of storage, respectively. Thus, tominimize the systematic errors from the absorbance changeduring the post-irradiation storage, it is recommended to keepthe films between the irradiation and absorbance measurementsin a dark cool place or to standardize the period between

irradiations and measurements in both calibrations and routinedose determinations.

3.5. Effect of the air humidity during irradiation on the doseresponse

Several films were irradiated simultaneously to 10 Gy in airatmospheres with different relative humidities to investigate theeffect of humidity levels on the dose response function (Fig. 10).The following exactly known relative humidities were achieved inthe air above saturated salt solutions in tightly closed jars at 25 1C(Greenspan, 1977) 33% (magnesium chloride), 53% (magnesiumnitrate), 75% (sodium chloride), and 94% (potassium nitrate). Therelative humidity, (RH) in an additional jar with dry silica gel wasassumed to be 0%. The films were stored in the jars for 72 h beforethe irradiation and remained in the jars during the irradiationitself.

The dose response increases slightly (within 5%) with increas-ing RH from 0% to 33% and then tends to be stable in the RH rangeof 33–75%. However, if RH increases further, the dose responsegrows dramatically. So, in order to minimize the effect of the RH ofthe environment during irradiations, it is advisable to pack the

Fig. 7. Radiation sensitivity of the HDDBU-containing PVB films as a function of theHDDBU concentration in the film.

Fig. 8. Pre-irradiation stability of the absorbances of the PVB films with 10 phr ofHDDBU stored under different conditions.

Fig. 9. Absorbances of the PVB films with 10 phr of HDDBU stored under differentconditions after the irradiation to 25 kGy.

Fig. 10. Response of the PVB films with 15 phr of HDDBU to 10 kGy as a function ofthe relative humidity of the air during the irradiation. Error bars represent 2s. Theabsorbances were measured after the irradiation.

A.A. Abdel-Fattah et al. / Applied Radiation and Isotopes 86 (2014) 21–27 25

films into sealed aluminum pouches in an atmosphere with the RHin the range of 33–75%.

3.6. Effect of irradiation temperature on the dose response

Sets of the film with 15 phr of HDDBU were irradiated to thesame dose 10 kGy in a temperature-controlled environment pro-vided by the temperature controller described in the experimentalsection. The film had been kept in the environment with thedesired temperature for 5 min before the irradiation and remainedtheir during the irradiation. Fig. 11 shows that there is a steepincrease in the response with increasing irradiation temperaturein the range of 30–50 1C. The temperature dependence can bedescribed with a polynomial function

ΔA mm�1 ¼ 7:857–0:271 Tþ6:891� 10�3 T2

with the correlation coefficient r2¼0.9995 in the entire studiedtemperature range of 20–50 1C. The average temperature coeffi-cients in the ranges 20–30 1C and 30–50 1C are approximately 1.22and 4.29%/oC, respectively. To eliminate systematic errors resultedfrom the irradiation temperature variations, it is strongly advisedto construct a calibration curve using dosimeters irradiated at thetemperature to be used in irradiations of future routine dosemeasurements (Sharpe and Miller, 2009).

4. Estimated overall uncertainty of determined doses

Uncertainty of a dose measurement can be defined as aparameter associated with the result of a measurement thatcharacterizes the dispersion of the values that could reasonablybe attributed to the measurand (ISO/ASTM 51707, 2004). Contribu-tions to the overall uncertainty can be classified into two cate-gories, namely, Type A (uA, evaluated by statistical methods from aseries of repeated observations) and Type B (uB, evaluated by non-statistical methods, for example, based on manufacturer–suppliedinformation) (ISO/ASTM 51707, 2004).

Sources of uncertainty in dose measurements with the pro-posed film system can be summarized as follows: calibration ofthe radiation source used for film calibration; irradiation itself(geometric factors, source decay correction, timer setting); batchnonuniformity; measurement of absorbance; environmentalfactors (temperature and humidity during the irradiation and

post-irradiation changes of the response); and the calibrationfunction fit.

Table 1 presents the uncertainty budget for measurements inthe dose range between 3 kGy and 50 kGy, which is suitable forsterilization and food irradiation. Some of these components areexplained in the footnotes to Table 1, while the others arediscussed below.

The uncertainty resulted from the batch nonuniformity (lotheterogeneity) was investigated by irradiating different sets offilms to different doses and analyzing them at 259 nm immedi-ately after irradiation. The following equation can be used toestimate this parameter (ISO/ASTM 51707, 2004; Sharpe andMiller, 2009):

u¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiΣiðni�1ÞðsiÞ2

Σiðni�1Þ

s;

where ni and si are the number of dosimeters and the coefficientof variation of the measured doses at a given dose level, respec-tively. The uncertainty was found to be 1.2%. This value inevitablyincludes, in addition to the the batch heterogeneity, effects of thevariation of the actual absorbed doses given to the dosimeters andof the variability in the performance of the measurement instru-ment and analysis procedures (Mehta, 2006).

The uncertainty of the analytical function chosen to fit theresponses of the calibration dosimeters will affect the overalluncertainty. The standard uncertainty of the fit was calculatedusing the following formula (Sharpe and Miller, 2009):

u¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiΣðresidualsÞ2

nd�nc

s;

where nd is the number of dosimeters and nc is the number ofvariable paramaters in the selected function. The values of theresiduals were provided by the commercial program TableCurve2D (Version 5.01, Jandel Scientific Software), which was used tofind the best function to fit the responses of the calibration films.The uncertainties of the fit were found to be 1.5% and 1.3% for thelow (3–50 kGy) and high (50–150 kGy) dose ranges, respectively.Absorbances of all individual calibration films, rather than theiraverages, were used in the uncertainty estimation. The standard

Fig. 11. Response of the PVB films with 15 phr of HDDBU to 10 kGy as a function ofthe irradiation temperature. Error bars represent 2s.

Table 1Uncertainties of dose measurements in the range of 3–50 kGy with PVB filmscontaining 15 phr HDDBU.

Source of uncertainty Type ofuncertainty

Standarduncertainty, %

Calibration of the radiation sourcea B 1.145Process of irradiation of calibration filmsb B 0.44Variations of the sensitivity of the

spectrophotometercA 0.035

Reproducibility of the absorbancemeasurementsd

A 0.38

Uniformity of the dosimeter batch A 1.20Uncertainty of the calibration curve fit A 1.55Irradiation temperature variations B 0.20Post-irradiation variations of the

responseA 0.43

Irradiation temperature effect A 2.47Combined standard uncertainty (uc), 1s 3.42Expanded uncertainty (2r) 6.84

a Taken from the NPL calibration certificate.b Includes geometry imperfections, source decay correction, timer setting and

nonuniformity of the gamma field (Mehta, 2006).c Estimated from 100 replicate measurements of the absorbance of irradiated

film to 25 kGy while the film was immobile in the sample holder.d Estimated from 100 replicate measurements of the absorbance of an

irradiated film with film reinserted into the holder after each measurement.

A.A. Abdel-Fattah et al. / Applied Radiation and Isotopes 86 (2014) 21–2726

uncertainty can be reduced by increasing the number of dosesgiven to the calibration films.

The temperature of the film dosimeter during the irradiationwill affect its dose response and, accordingly, the determined dose.Assuming that the dosimeters are used within the temperaturerange of 30–50 1C, the temperature coefficient is approximately4.29%/1C. If the uncertainty in the difference between the irradia-tion temperatures during the calibration and the dose measure-ment is 71 1C and the temperature effect has a rectangularprobability distribution (divisor √3Þ (IAEA, 2013), the standarduncertainty related to the temperature effect will be

u ð1sÞ ¼ ð1 � 4:29Þffiffiffi3

p ¼ 2:47 %:

If the dosimeters are used at lower temperatures (20–30 1C), theuncertainty will decrease down to 0.71%. This component of theuncertainty can by smaller if the dosimetry system is calibrated atirradiation temperatures close to those actually used in theirradiation facilities (ISO/ASTM 51261, 2004).

The instability of the absorbance of the film after irradiation isyet another factor that contributes to the uncertainty of theresulted dose (Soliman and Abdel-Fattah, 2012). Here, we assumethat the absorbance measurements in calibration and routine dosedeterminations are performed in similar periods of time afterirradiation. The study of the post-irradiation color stability showedthat the variations of the absorbances during 24 h after irradiationare within 1.5%. So, if the periods between the absorbancemeasurements in calibration and dose determination are within712 or 724 h, the standard uncertainties will equal 0.43% and0.87%, respectively, provided that the divisor √3 is used (ISO/ASTM 51707, 2004).

A similar analysis showed that the overall uncertainties ofdoses measured in the ranges of 3–50 and 50–100 kGy would beabout 6.845% and 6.34%, respectively (2s). These uncertainties areacceptable for dose measurements in radiation process control.The uncertainties go down to less than 5% if the dosimeters areused within the temperature range 20–30 1C and the absorbancesare measured in similar periods of time after the irradiations in thecalibration and dose determinations. It is assumed that calibrationfilms have been irradiated under radiation conditions very similarto those used in the irradiation of the test films. If this assumptionis wrong, an unknown error in the determined dose may occur.The standard uncertainty of the measured dose can be reduced byincreasing the number of replicate films at each dose point and bycorrecting the dosimeter response for irradiation temperature(Sharpe and Miller, 2009).

5. Conclusion

A radiation-sensitive compound HDDBU was synthesized bythe reaction of butyl isocyanate with freshly prepared 2,4-hex-adiyn-1,6-diol. The compound, characterized with FTIR spectro-scopy, was introduced into a PVB film to prepare a radiationdosimeter suitable for a wide range of applications in radiationprocessing. XRD diffraction showed that HDDBU in PVB was in anon-crystalline form and radiation-induced polymerization wasrandom rather than topochemical. The spectrum of HDDBU/PVBfilms undergoes a change upon gamma irradiation. Two newbands, at 273 nm and 285 nm, appear, and their intensitiesincrease with the radiation dose, as do intensities of the bandsat 233, 245, and 259 nm originally present in the spectrum ofHDDBU. The dosimeters with appropriate concentrations ofHDDBU can be used for dose measurements in the range 3–150 kGy. They are suitable for use in monitoring various industrial

processes, such as food irradiation, radiation sterilization ofmedical devices, and polymer modification. The response of thefilmwas not affected by variations of relative humidity of the air inthe range of (33–75)%; however, it was significantly affected byvariations of the irradiation temperature in the range of 30–50 1C.To minimize the environmental effects, it is strongly recom-mended to calibrate the dosimeters under actual radiation proces-sing conditions in the production facility using an independentreference dosimetry system. The overall uncertainty of absorbeddose determined with this system is below 6.2% (2s).

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