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On induced-modifications in optical properties of Makrofol® DE 1-1 SSNTD by UVB and UVA
Results in Physics 7 (2017) 1361–1366
Contents lists available at ScienceDirect
Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics
On induced-modifications in optical properties of MakrofolÒ DE 1-1 SSNTD by UVB and UVA A. Al-Amri a,b,⇑, M. El Ghazaly c,d, M.S. Abdel-Aal a,e a
Department of Physics, Faculty of Science, Taif University, P.O. Box 888, Taif, Saudi Arabia Department of Physics, Faculty of Science in Al Namas, Bisha University, Saudi Arabia c Department of Physics, Faculty of Science, Zagazig University, PO 44519, Zagazig, Egypt d Department of Physiology, Faculty of Medicine, Taif University, P.O. Box 888, Taif, Saudi Arabia e Department Spectroscopy, National Research Centre, 12311, Dokki, Cairo, Egypt b
a r t i c l e
i n f o
Article history: Received 29 November 2016 Received in revised form 19 March 2017 Accepted 19 March 2017 Available online 30 March 2017
a b s t r a c t The induced modifications in the optical properties of MakrofolÒ DE 1-1 solid state nuclear track detectors upon irradiation by UVB (302 nm) and UVA (365 nm) were characterized and compared. MakrofolÒ DE 1-1 detectors were irradiated separately for different durations with UVB (302 nm) and UVA (365 nm). The measurements revealed insignificant changes were observed at all in UVA (365 nm)irradiated MakrofolÒ DE 1-1, irrespective the irradiation time (dose). All UVB (302 nm)-irradiated MakrofolÒ DE 1-1 detectors show a substantial red shift in UV–Vis spectra and a continuous increase in absorbance as the exposure time (Dose) to UVB increases. UVC-irradiated MakrofolÒ DE 1-1 exhibits absorption bands at 315 ± 5 nm in UV–visible spectra. The absorption increases exponential with the increasing the UVB irradiation time gets saturated started from 75 h to 400 h. In the visible light range no significant changes were observed in MakrofolÒ DE 1-1 detector irrespective the exposure time to UVB of 302 nm. It is found that the direct band gap is higher than indirect band gap and both decrease with the increase in the irradiation time of UVB of 302 nm. The obtained results of the Urbach energy and carbon atoms per cluster indicate that both increase with the increase in the irradiation time to UVB (302 nm). The induced modification in the optical properties of MakrofolÒ DE 1-1 can be used in UVB dosimetry, meanwhile it is not applicable for UVA of 365 nm. Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).
1. Introduction Solid state nuclear track detectors (SSNTDs), which made up of polymers, are utilized as detecting mechanism in physics experiment and for industrial applications [1,2]. Significant works characterizing the response of SSNTDs has been published in the last four decades; a recent comprehensive paper on SSNTDs has been published by Nikezic and Yu along with a comprehensive bibliography of studies on SSNTDs [3]. One of the well-known polymer-based SSNTDs is MakrofolÒ DE, which are widely used to prepare track-etched membranes, alpha, neutron, and charged particles radiography, cosmic rays detection, and in the radiation dosimetry even for low linear energy transfer radiation such as Gamma-rays-and ultraviolet radiation [4–10]. However, all these applications rely either on the observation of the nuclear tracks of heavy ions that are ⇑ Corresponding author at: Department of Physics, Faculty of Science, Taif University, P.O. Box 888, Taif, Saudi Arabia. E-mail address: [email protected] (A. Al-Amri).
developed by chemical etching in a suitable etchant, under an optical microscope, or by measuring the induced modifications in the physical properties of the detector that is induced by low linear energy transfer radiations through chemical structure modifications [11–14]. Using polycarbonate-based SSNTDs in LLET radiation dosimetry based normally on the induced physio-chemical modifications in detector material, which should be different from detector to detector and even for the same detector depending on many parameters including manufacturing procedure, production date, and storing procedure. Therefore, different polycarbonate-based SSNTDs react differently with LLET radiation of the same type and same dose. Polymers degradation upon exposure to UVB radiation of different wavelengths has been investigated, but the data available with MakrofolÒ DE 1-1 is quite insufficient [11]. The repeating unit of the MakrofolÒ DE 1-1 detector is presented in Fig. 1, while the aromatic group is known for reduction the polycarbonate irradiation sensitivity as a result of delocalization of the excitation energy, Carbonyl group C@O is known for higher irradiation sensitivity [3,11].
http://dx.doi.org/10.1016/j.rinp.2017.03.024 2211-3797/Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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Fig. 1. The repeating unit of MakrofolÒ DE 1-1 polycarbonate.
Ultraviolet radiation with its wide spectrum of wavelength ranging from 100 to 400 nm is divided by the international Commission Illumination (CIE) into three regions according to wavelength, these are: UVA in the range 315 to 400 nm, UVB in the wavelength range from 280 to 315 nm, which are the main components reaching the earth surface, and UVC in the wavelength range from 100 to 280 nm [15], which is completely absorbed in the most outer atmosphere layers. However, ultraviolet radiation with such wide spectrum would be absorbed and interacted differently in SSNTDs. The purpose of this paper is to characterize and compare the induced modifications in the optical properties of MakrofolÒ DE 1-1 solid state nuclear track detector upon irradiation of UVB (302 nm) and UVA (365 nm) for different durations. UV–Vis absorbance spectra will be measured and discussed as a function in the exposure time to UVB and UVA. The indirect and direct band gap energy will be calculated and correlation between change their changes and UVB and UVA exposure time (Dose) will be established. Furthermore, the Urbach’s energy and number of carbon atoms per cluster as a function of the UVB and UVA doses will be reported. 2. Material and method MakrofolÒ DE1-1 (Bisphenol-A polycarbonate) detector, which is of the molecular formula of C16H14O3, the molecular weight of 254 and density of 1.2 g/cm3, was supplied by Bayer AG Leverkusen, Germany [16,17]. MakrofolÒ DE 1-1 samples of 4 cm2 were cut from a large sheet of thickness 250 lm. The MakrofolÒ DE 1-1 samples were irradiated with ultraviolet radiation (UVB) of 302 nm wavelength and UVA of 365 nm wavelength for different durations at the same distance of 5 cm in air from an UVLMS38lampofapower8 W [18]. For ultraviolet radiation of wavelength 302 exposure of 1 h corresponding to 7.53 Joule/cm2, while for ultraviolet radiation of wavelength 365 nm exposure of 1 h corresponding to 7.94 J/cm2 However, the thermal effects of the UVC lamp were minimized by fixing the sample temperature at 303 K. The mass of all detectors were measured before and after irradiation with the aid of sensitive balance of 0.0001 g sensitivity. The MakrofolÒ DE 1-1 detectors were digitized using a Canon CanoScan 9000F Mark II flatbed scanner [19]and images were analyzed using ImageJ code [20]. UV–visible spectra of the SSNTDs were measured using an UV–visible spectrophotometer(Model Spectro dual split beam,UVS-2700) in the wavelengths range of 190–900 nm keeping air as a Ref. [21]. 3. Results and discussion 3.1. Color change b UVB (302 nm) and UVA (365 nm) Upon UVB (302 nm) irradiation of MakrofolÒ DE 1-1 for different durations even for 400 h, there was insignificant change in MakrofolÒ DE 1-1 mass before and after irradiation. However, the colorless MakrofolÒ DE 1-1 was changed to yellow color, which indicates the occurrence of induced modifications in the optical properties of detectors by UVB of 302 nm. However, to quantitative analysis of color change in MakrofolÒ DE 1-1 by UVB of 302 nm
Fig. 2. [a] the digitized image of pristine MakrofolÒ DE 1-1 and [b] UVB (302 nm)irradiated MakrofolÒ DE 1-1 for 400 h. [C] is the corresponding histograms of grey level distribution for pristine and UVB irradiated MakrofolÒ DE 1-1.
irradiation, MakrofolÒ DE 1-1 samples were digitized using a Canon CanoScan 9000F Mark II flatbed scanner in the reflection scan mode and at resolution of 600 dpi and dynamic range of 28, and analyzed using free ImageJ software [20]. Fig. 2. presents [a] the digitized image of pristine MakrofolÒ DE 1-1 and [b] the digitized image of UVB (302 nm)-irradiated MakrofolÒ DE 1-1 for 400 h. [C] is the corresponding histograms of grey level distribution for pristine and UVB irradiated MakrofolÒ De 1-1. As can be seen, the UVB irradiated MakrofolÒ DE 1-1 is darker than pristine MakrofolÒ DE 1-1, which indicates the photodegradation of MakrofolÒ DE 1-1 by UVB. The grey level histograms of both pristine and UVB irradiated MakrofolÒ DE 1-1 is present on the same graph to show the effect of UVB. The grey level histogram of pristine is fitted using Gauss function
FðgÞ ¼ 22806 þ 13243Exp½ðg 244Þ2 =1:13 The center of the grey level is about 244 which indicates high transparency of detector which agree with the data [16,17], and the standard deviation is about 0.64. The data of UVB irradiated MakrofolÒ DE 1-1 for 400 h are fitted as well with the gauss function of
FðgÞ ¼ 76307 þ 8632Exp½ðg 231Þ2 =5:65 The center of the grey level is about 231 which indicates loss of the transparency of MakrofolÒ DE 1-1 detector which and the standard deviation is about 1.43. However, the increase in the standard deviation of the irradiated MakrofolÒ DE 1-1 shows the increase the inhomogeneous in the detector material by UVB of 302 nm. 3.2. UV–Vis absorption spectra The extinction coefficient of MakrofolÒDE1-1 in the UVB range of 302 nm shows that its photodegradation may be considered exclusively as a surface reaction limited to topmost few microns thick layer of the MakrofolÒDE 1-1 detector. Fig. 3. Presents the
A. Al-Amri et al. / Results in Physics 7 (2017) 1361–1366
Fig. 3. UV–Vis absorption spectra at different durations for pristine and UVB (302 nm)-irradiated MakrofolÒDE 1-1.
UV–Vis absorption spectra of the pristine and UVB (302 nm)–irradiated MakrofolÒDE 1-1 detector for different irradiation times [23,24]. There is a high absorbance band at shorter wavelength from 190 to 280 nm that is completely saturated with noise. This high absorbance, however, is attributed to a transition from a non-bonding orbital to p⁄ (n ? p⁄) and p ? p⁄ in C@O (Carbonyl group) and C@C. Staring from 280 nm at the absorption decreases sharply to 300 nm and the absorbance becomes almost constant from 300 nm to 450 nm and amounts to 0.8 ± 0.05. A new absorbance band is formed at about 310 nm, where the absorbance at this band increases with the increase in the irradiation time to UVB of 302 nm. This high absorbance, however, is attributed to a transition from a non-bonding orbital to p⁄ (n ? p⁄) and p ? p⁄ in C@O (Carbonyl group)and C@C [22]. Staring from 280 nm at the absorption decreases sharply to 300 nm and the absorbance becomes almost constant from 300 nm to 450 nm and amounts to 0.1 ± 0.5. As can be seen from Fig. 3 there exist a continuous red shift (shift towards longer wavelength in the UV–Vis spectra) by increasing the exposure time to ultraviolet radiation UVB (302 nm). The photochemistry of MakrofolÒDE 1-1 detector is strongly correlated with the spectral distribution of ultraviolet radiation either UVB of 302 nm either 365 nm. At wavelength of 302 nm mainly direct excitation of MakrofolÒDE 1-1 take place, beginning with the scission of the CO-O bond followed by two successive Photo-Fires rearrangements of aromatic carbonate group and leading to formation of phenylsalicylate and dihydroxybenzophenone units. However, the minor changes in UV–Vis spectra were elucidated by calculated the difference between the UVB (302) irradiated and pristine MakrofolÒDE 1-1. These difference spectra indicate the existence of a clear band at 280 nm and clear band at about 317 nm which increase with the increase in the irradiation time to UVB. As presented in Fig. 3. The formation of the band between 305 and 325 nm is assigned to the formation of a phenylsalicylate moiety that is formed by the first photo-Fires rearrangement. This is, however, is expected for UVB (302 nm) [23]. The second shoulder at about 350 nm attributed to the formation of dihydroxybenzophenone moiety, which is the second rearrangement step in the photo-Fries rearrangement, which is not observed by Diepens [11]. The regular shift in the absorption edge of UVB (302 nm)-irradiated MakrofolÒDE 1-1 reveals the reduction in the energy difference between HOMO-LUMO, which shows the possibility of tuning the optical properties of MakrofolÒDE 1-1 by exposure to UVB of 302 nm for different durations.
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The extinction coefficient of MakrofolÒDE 1-1 detector in the UVA range of 365 nm shows that its photodegradation may be considered exclusively as a bulk reaction spread over the all thickness of the MakrofolÒDE 1-1 detector, nevertheless, the ultraviolet radiation of 365 nm doesn’t absorbed by the MakrofolÒDE 1-1 detector since the absorbance at 365 nm amounts to 0.06 ± 0.02, which corresponding to attenuation coefficient of 5.6 cm1, as can be seen in Fig. 4. The influences of UVA of 365 nm irradiation for different duration on the MakrofolÒ DE 1-1 detector were monitored using UV–Vis spectrometer. On the UV–Vis exemplified in Fig. 4., which shows the absorbance of pristine and 400 h irradiated with UVA of 365 nm, no really significant changes were observed between pristine and 400 h irradiated MakrofolÒ DE 1-1. However, the results agree with the theoretical predication from the calculation of the attenuation coefficient as discussed above. Three wavelengths in the UV–Vis absorption spectra of 310, 350, and 550 have been selected to examine and characterize the correlation between the irradiation time (Dose) and the induced modifications in the UV–Vis absorption spectra of the MakrofolÒDE 1-1 detector are presented in Fig. 5. The absorbance of UVB (302 nm) irradiated MakrofolÒDE 1-1 detector at 310 and 350 nm
Fig. 4. UV–Vis absorption spectra at different durations for pristine and UVA (365 nm)-irradiated MakrofolÒDE 1-1.
Fig. 5. The absorbance band intensities versus the exposure time for the UVBirradiated MakrofolÒ DE 1-1 detector.
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is increased linearly for short irradiation time up to 35 h, the increment rate decreases with the increase in the exposure time getting saturated especially for extreme exposure time of 400 h. These results, however, confirm a formation a photo-stabilized groups on the irradiated surface of the MakrofolÒDE 1-1 detector, which hinder the further modification and the bulk MakrofolÒDE 1-1 detector. The parameterization of the absorbance at 310 nm as a function of the UVB (302 nm) irradiation time (Dose) can be carried out by fitting the data using the exponential growth function;
AbsðtExp: Þ ¼ 1:49 1:22Exp½0:019t Exp: :
ð1Þ
The parameterization of the absorbance at 350 nm as a function of the UVB (302 nm) irradiation time (Dose) can be carried out by the fitting using the exponential growth function;
AbsðtExp: Þ ¼ 1:08 0:97Exp½0:008t Exp:
ð2Þ
For the absorbance at 550 nm (in visible light region) of MakrofolÒ DE 1-1 detector, no significant changes in the absorbance were observed even for extreme exposure time of 400 h, the data are fitted using the a linear function
AbsðtExp: Þ ¼ 0:067 2 105 tExp:
Fig. 6. The indirect optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒDE 1-1 for different durations.
ð3Þ
The standard deviation is 0.43 and R equals to 0.12 and P amounts to 70%. The rate linear regression of the fitting line is about 0.00005, which indicates stability of the MakrofolÒ DE 1-1 detector in visible light region and no correlation at all between absorbance and irradiation dose at 550 nm in the absorption spectra. 3.3. Optical energy gaps UV–Vis spectroscopy can be applied to determine the modification in the optical properties of the MakrofolÒDE 1-1, including the determination of the inducedtransitions and for characterization the band structure and optical energy gaps. In principle, the optical absorption coefficient is correlated with energy of the incident electromagnetic radiation. The optical absorption coefficient (a) can be determined in terms of absorbance Abs(hm), which is measured by UV–Vis spectroscopy, and the thickness t measured in cm by [25]:
aðhmÞ ¼ 2:303
AbsðhmÞ t
ð4Þ
Fig. 7. The direct optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒDE 1-1 for different durations.
Meanwhile, the optical band gap (Eg) is correlated with optical absorption coefficient (a) and the photons energy (hm) the by Tauc’s expression [26],
aðhmÞ ¼
Cðhm Eg Þm ; hm
ð5Þ
where m characterizes the transition process in the K-space, which can assume the values 0.5, 1.5, 2, and 3 for direct allowed, direct forbidden, indirect allowed, and indirect forbidden, respectively [17]. C is known as band tailing parameter that amounts to C ¼ 4pr=ncEc where c is the speed of the light, r is the minimum conductivity, n is the refractive index, and Ec is the width of the trail states distribution. However, C correlates with the transition probability. The direct and indirect optical band gap energies are evaluated by plotting (ahm)2 and (ahm)0.5against the photon energy (hm). Considering the linear part of the fundamental absorption edge of the UV–Vis spectra, the best fit lines were employed to determine on the energy axis. Fig. 5. Presents the indirect optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒ DE 1-1 for different durations up to 400 h. There exists a continuous reduction in the optical band gap towards the lower energy. The indirect optical band gaps
Fig. 8. The dependence of natural logarithm of the absorption coefficient a on photon energy for a pristine and irradiated MakrofolÒDE 1-1 with UV wave of 302 nm wavelength.
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Table 1 Direct, indirect energy gaps, Urbach’s energy values, and the corresponding number of carbon atoms in the cluster (M) for MakrofolÒDE1-1 detectorirradiated with UVB of 365 nm for different durations. Exposure time [h]
Direct Eg [eV]
Indirect Eg[eV]
Eu[eV]
M direct
M Indirect
0 1 2 5 10 15 20 35 75 115 300 400
4.23 ± 0.02 4.21 ± 0.02 4.21 ± 0.02 4.19 ± 0.02 4.16 ± 0.02 4.14 ± 0.02 4.11 ± 0.02 4.07 ± 0.02 4.02 ± 0.02 4 ± 0.02 3.94 ± 0.02 3.90 ± 0.02
3.96 ± 0.02 3.87 ± 0.02 3.84 ± 0.02 3.82 ± 0.02 3.76 ± 0.02 3.68. ± 0.02 3.65 ± 0.02 3.59 ± 0.02 3.57 ± 0.02 3.52 ± 0.02 3.48 ± 0.02 3.45 ± 0.02
0.13 0.15 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.21 0.25 0.27
65 66 66 67 67 68 69 71 72 73 75 77
75 78 79 80 83 86 88 91 91 94 97 98
for different UVB (302 nm)-irradiation time decreases with the increase in the irradiation time. Fig. 7 shows the direct optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒ DE 1-1 for different durations up to 400 h. There exists a continuous reduction in the optical band gap towards the lower energy. The indirect optical band gaps for different UVCB (302 nm)-irradiation time decreases with the increase in the irradiation time. The values of the direct and indirect bands are summarized in Table 1 with their standard errors. Some characteristic aspects regarding the direct and indirect band gaps could be obtained from Table 1; these are: (1) observation of the coexistence of direct and indirect band gaps in UV (302)-irradiated MakrofolÒ DE 1-1, (2) the direct band gap is higher than the corresponding indirect band gap for UVB (302 nm)-irradiated MakrofolÒ DE 1-1, and (3) there was significant change in both direct and indirect band gaps, which suggested the possibility to use the MakrofolÒ DE 1-1 as UVB (302 nm) dosimeter. The energy gap Eg changes points to the formation of photochemical compounds between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy states. Urbach energy Eu, which is corresponding to the localized state width in the optical band gap, is related to the absorption coefficient and photon energy by the following equation [27]:
aðhmÞ ¼ a Exp
hm : Eu
ð6Þ
Here, ao is a constant and a(hm) is the absorption coefficient, Eu is the Urbach energy or the energy of the band tail. The Urbach energies are calculated by considering the inverse of the slop of the linear part of plotting curve of Ln [a(hm)] against (hm) as depicted in Fig. 6. The Urbach energies of pristine and UVB (302 nm) MakrofolÒ DE 1-1 for different durations are summarized in Table 1. One can observe that Urbach energy increases from 0.13 eV for pristine MakrofolÒ DE 1-1 detector and decreases to be around 0.27 eV at exposure time of 400 h (see Fig. 8). The energy of the optical band gaps depends on the number, type, and structural arrangement of the carbon bonds per molecule. Concerning the MakrofolÒ DE 1-1 as Bisphenol-A poly carbonate and considering Robertson’s relation that is reformulated by Fink [28], the number of the carbon atoms, M, per cluster is calculated using the following equation
34:3 Eg ¼ pffiffiffiffiffi M
ð7Þ
The values of carbon atoms per cluster in the pristine and UVB (302 nm) MakrofolÒ DE 1-1 are summarized in Table 1 for direct and indirect band gaps. The number of carbon atoms per cluster for direct band gap is found to increase as the irradiation time to
UVB of 302 nm from 65 for pristine to 77 for UVB irradiated MakrofolÒ DE 1-1 for 400 h for direct energy gap and from 75 for pristine to 98 for 400 h. However, according to the results summarized in Table 1, the UVB (302 nm) MakrofolÒ DE 1-1 detector is instable against UVB (302 nm) even for short exposure time. 4. Conclusion Throughout the current work, the induced modifications in the optical properties of MakrofolÒDE 1-1 solid state nuclear track detectors upon irradiation by UVB (302 nm) and UVA (365 nm) were characterized. Substantial red shifts in UV–Vis spectra and continuous increase in absorbance as the exposure time (Dose) to UVB increases were observed, meanwhile, there was insignificant change in the UV–Vis spectra of MakrofolÒDE 1-1 upon irradiation by UVA (365 nm), irrespective the irradiation time (dose). UVCirradiated MakrofolÒDE 1-1 exhibits absorption bands at 280 ± 5 nm and 315 ± 5 nm in UV–visible spectra, which are increasing exponentially as the irradiation time (dose) increase getting saturated at prolonged exposure times more than 35 h. The direct band gap is higher than indirect band gap and both decrease with the increase in the irradiation time of UVB of 302 nm. The Urbach energy and carbon atoms per cluster increase with the increase in the irradiation time. The induced modification in the optical properties of MakrofolÒDE 1-1 can be used in UVB dosimetry which it is not applicable for UVA of 365 nm. References [1] Durrani SA, Bull RK. Solid state nuclear track detection, principles, methods and applications. Pergamon Press; 1987. [2] Fleischer RL, Price PB, Walker RM. Nuclear tracks in solids: principles and applications. Berkeley: University of California Press; 1975. [3] Nikezic D, Yu KN. Mater Sci Eng 2004;46:51–123. [4] Pugliesi R, Pereira MA. Instrum Methods B 2002;484:613. [5] El Ghazaly M. Radiat Eff Defects Solids 2011;167:141. [6] Salamon MH, Price PB, Drach J. Nucl Instrum Methods Phys Res B 1986;17 (2):173. [7] Pugliesia F, Stanojev Pereira MA, Pugliesia R, Diasa MS. Appl Radiat Isot 2014;89:1. [8] Singh L, Samra KS. J Macromol Sci Part B Phys 2007;46:1041. [9] Fink D, Ghosh S, Klett R, Dwivedi KK, Kobayashi Y, Hirata K, Vacik J, Hnatowicz V, Cervena J, Chadderton LT. Nucl Instrum Methods Phys Res B 1998;146:486. [10] Wu T, Lee S, Chen W. Macromolecules 1995;28:5751. [11] Diepens M. Photodegradation and stability of bisphenol a polycarbonate in weathering conditions. Netherland: Eindhoven University of Technology; 2009. [12] Shah H, Rufus I, Hoyle C. Macromolecules 1994;27:553–61. [13] El Ghazaly M. Radiat Eff Def Solids 2012;167(2):141–8. [14] El Ghazaly M. Res Phys 2016;3:634–9. [15] Diffey BL. Rev Phys Med Biol 1991;36(3):299–328. [16] http://www.anilinkompaniet.se/img/folie/Makrofol-DE-1-1-ISO.pdf (access date 08.06.2014). [17] http://www.films.covestro.com/Products/Makrofol/ProductList.aspx (access date 09.07.2016). [18] https://www.uvp.com/elseries.html (access date 25.11.2016).
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[19] http://www.canon.com.cy/scanners/flatbed-scanners/canoscan_ 9000f_markii/ (access date 25.11.2016). [20] https://imagej.nih.gov/ij/(access date 25.11.2016). [21] http://www.labomed.com/Dual.htm (access date 22.06.2016). [22] Hareesh K, Pandey AK, Sangappa Y, Bhat Ravishankar, Venkataraman A, Sanjeev Ganesh. Nucl Instrum Methods B 2013;295:61–8. [23] Geretovszky Zs, Hopp B, Bertóti I, Boyd IW. Appl Surf Sci 2002;186:85–90.
[24] [25] [26] [27] [28]
Rivaton A, Sallet D, Lemaire J. Polym Photochem 1983;3:463–81. Migahed M, Zidan HM. Cur Appl Phys 2006;6(1):91–6. Tauc J, Grigorovici R, Vancu A. Phys Stat Sol 1966;15:627–37. Urbach F. Phys Rev 1953;92:1324–953. Fink D, Chung WH, Klett R, Schmoldt A, Cardoso J, Montiel R, Vazquez MH, Wang L, Hosoi F, Omichi H, Goppelt-Langer P. Radiat Eff Defects Solids 1995;133:193–208.
Contents lists available at ScienceDirect
Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics
On induced-modifications in optical properties of MakrofolÒ DE 1-1 SSNTD by UVB and UVA A. Al-Amri a,b,⇑, M. El Ghazaly c,d, M.S. Abdel-Aal a,e a
Department of Physics, Faculty of Science, Taif University, P.O. Box 888, Taif, Saudi Arabia Department of Physics, Faculty of Science in Al Namas, Bisha University, Saudi Arabia c Department of Physics, Faculty of Science, Zagazig University, PO 44519, Zagazig, Egypt d Department of Physiology, Faculty of Medicine, Taif University, P.O. Box 888, Taif, Saudi Arabia e Department Spectroscopy, National Research Centre, 12311, Dokki, Cairo, Egypt b
a r t i c l e
i n f o
Article history: Received 29 November 2016 Received in revised form 19 March 2017 Accepted 19 March 2017 Available online 30 March 2017
a b s t r a c t The induced modifications in the optical properties of MakrofolÒ DE 1-1 solid state nuclear track detectors upon irradiation by UVB (302 nm) and UVA (365 nm) were characterized and compared. MakrofolÒ DE 1-1 detectors were irradiated separately for different durations with UVB (302 nm) and UVA (365 nm). The measurements revealed insignificant changes were observed at all in UVA (365 nm)irradiated MakrofolÒ DE 1-1, irrespective the irradiation time (dose). All UVB (302 nm)-irradiated MakrofolÒ DE 1-1 detectors show a substantial red shift in UV–Vis spectra and a continuous increase in absorbance as the exposure time (Dose) to UVB increases. UVC-irradiated MakrofolÒ DE 1-1 exhibits absorption bands at 315 ± 5 nm in UV–visible spectra. The absorption increases exponential with the increasing the UVB irradiation time gets saturated started from 75 h to 400 h. In the visible light range no significant changes were observed in MakrofolÒ DE 1-1 detector irrespective the exposure time to UVB of 302 nm. It is found that the direct band gap is higher than indirect band gap and both decrease with the increase in the irradiation time of UVB of 302 nm. The obtained results of the Urbach energy and carbon atoms per cluster indicate that both increase with the increase in the irradiation time to UVB (302 nm). The induced modification in the optical properties of MakrofolÒ DE 1-1 can be used in UVB dosimetry, meanwhile it is not applicable for UVA of 365 nm. Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).
1. Introduction Solid state nuclear track detectors (SSNTDs), which made up of polymers, are utilized as detecting mechanism in physics experiment and for industrial applications [1,2]. Significant works characterizing the response of SSNTDs has been published in the last four decades; a recent comprehensive paper on SSNTDs has been published by Nikezic and Yu along with a comprehensive bibliography of studies on SSNTDs [3]. One of the well-known polymer-based SSNTDs is MakrofolÒ DE, which are widely used to prepare track-etched membranes, alpha, neutron, and charged particles radiography, cosmic rays detection, and in the radiation dosimetry even for low linear energy transfer radiation such as Gamma-rays-and ultraviolet radiation [4–10]. However, all these applications rely either on the observation of the nuclear tracks of heavy ions that are ⇑ Corresponding author at: Department of Physics, Faculty of Science, Taif University, P.O. Box 888, Taif, Saudi Arabia. E-mail address: [email protected] (A. Al-Amri).
developed by chemical etching in a suitable etchant, under an optical microscope, or by measuring the induced modifications in the physical properties of the detector that is induced by low linear energy transfer radiations through chemical structure modifications [11–14]. Using polycarbonate-based SSNTDs in LLET radiation dosimetry based normally on the induced physio-chemical modifications in detector material, which should be different from detector to detector and even for the same detector depending on many parameters including manufacturing procedure, production date, and storing procedure. Therefore, different polycarbonate-based SSNTDs react differently with LLET radiation of the same type and same dose. Polymers degradation upon exposure to UVB radiation of different wavelengths has been investigated, but the data available with MakrofolÒ DE 1-1 is quite insufficient [11]. The repeating unit of the MakrofolÒ DE 1-1 detector is presented in Fig. 1, while the aromatic group is known for reduction the polycarbonate irradiation sensitivity as a result of delocalization of the excitation energy, Carbonyl group C@O is known for higher irradiation sensitivity [3,11].
http://dx.doi.org/10.1016/j.rinp.2017.03.024 2211-3797/Ó 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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Fig. 1. The repeating unit of MakrofolÒ DE 1-1 polycarbonate.
Ultraviolet radiation with its wide spectrum of wavelength ranging from 100 to 400 nm is divided by the international Commission Illumination (CIE) into three regions according to wavelength, these are: UVA in the range 315 to 400 nm, UVB in the wavelength range from 280 to 315 nm, which are the main components reaching the earth surface, and UVC in the wavelength range from 100 to 280 nm [15], which is completely absorbed in the most outer atmosphere layers. However, ultraviolet radiation with such wide spectrum would be absorbed and interacted differently in SSNTDs. The purpose of this paper is to characterize and compare the induced modifications in the optical properties of MakrofolÒ DE 1-1 solid state nuclear track detector upon irradiation of UVB (302 nm) and UVA (365 nm) for different durations. UV–Vis absorbance spectra will be measured and discussed as a function in the exposure time to UVB and UVA. The indirect and direct band gap energy will be calculated and correlation between change their changes and UVB and UVA exposure time (Dose) will be established. Furthermore, the Urbach’s energy and number of carbon atoms per cluster as a function of the UVB and UVA doses will be reported. 2. Material and method MakrofolÒ DE1-1 (Bisphenol-A polycarbonate) detector, which is of the molecular formula of C16H14O3, the molecular weight of 254 and density of 1.2 g/cm3, was supplied by Bayer AG Leverkusen, Germany [16,17]. MakrofolÒ DE 1-1 samples of 4 cm2 were cut from a large sheet of thickness 250 lm. The MakrofolÒ DE 1-1 samples were irradiated with ultraviolet radiation (UVB) of 302 nm wavelength and UVA of 365 nm wavelength for different durations at the same distance of 5 cm in air from an UVLMS38lampofapower8 W [18]. For ultraviolet radiation of wavelength 302 exposure of 1 h corresponding to 7.53 Joule/cm2, while for ultraviolet radiation of wavelength 365 nm exposure of 1 h corresponding to 7.94 J/cm2 However, the thermal effects of the UVC lamp were minimized by fixing the sample temperature at 303 K. The mass of all detectors were measured before and after irradiation with the aid of sensitive balance of 0.0001 g sensitivity. The MakrofolÒ DE 1-1 detectors were digitized using a Canon CanoScan 9000F Mark II flatbed scanner [19]and images were analyzed using ImageJ code [20]. UV–visible spectra of the SSNTDs were measured using an UV–visible spectrophotometer(Model Spectro dual split beam,UVS-2700) in the wavelengths range of 190–900 nm keeping air as a Ref. [21]. 3. Results and discussion 3.1. Color change b UVB (302 nm) and UVA (365 nm) Upon UVB (302 nm) irradiation of MakrofolÒ DE 1-1 for different durations even for 400 h, there was insignificant change in MakrofolÒ DE 1-1 mass before and after irradiation. However, the colorless MakrofolÒ DE 1-1 was changed to yellow color, which indicates the occurrence of induced modifications in the optical properties of detectors by UVB of 302 nm. However, to quantitative analysis of color change in MakrofolÒ DE 1-1 by UVB of 302 nm
Fig. 2. [a] the digitized image of pristine MakrofolÒ DE 1-1 and [b] UVB (302 nm)irradiated MakrofolÒ DE 1-1 for 400 h. [C] is the corresponding histograms of grey level distribution for pristine and UVB irradiated MakrofolÒ DE 1-1.
irradiation, MakrofolÒ DE 1-1 samples were digitized using a Canon CanoScan 9000F Mark II flatbed scanner in the reflection scan mode and at resolution of 600 dpi and dynamic range of 28, and analyzed using free ImageJ software [20]. Fig. 2. presents [a] the digitized image of pristine MakrofolÒ DE 1-1 and [b] the digitized image of UVB (302 nm)-irradiated MakrofolÒ DE 1-1 for 400 h. [C] is the corresponding histograms of grey level distribution for pristine and UVB irradiated MakrofolÒ De 1-1. As can be seen, the UVB irradiated MakrofolÒ DE 1-1 is darker than pristine MakrofolÒ DE 1-1, which indicates the photodegradation of MakrofolÒ DE 1-1 by UVB. The grey level histograms of both pristine and UVB irradiated MakrofolÒ DE 1-1 is present on the same graph to show the effect of UVB. The grey level histogram of pristine is fitted using Gauss function
FðgÞ ¼ 22806 þ 13243Exp½ðg 244Þ2 =1:13 The center of the grey level is about 244 which indicates high transparency of detector which agree with the data [16,17], and the standard deviation is about 0.64. The data of UVB irradiated MakrofolÒ DE 1-1 for 400 h are fitted as well with the gauss function of
FðgÞ ¼ 76307 þ 8632Exp½ðg 231Þ2 =5:65 The center of the grey level is about 231 which indicates loss of the transparency of MakrofolÒ DE 1-1 detector which and the standard deviation is about 1.43. However, the increase in the standard deviation of the irradiated MakrofolÒ DE 1-1 shows the increase the inhomogeneous in the detector material by UVB of 302 nm. 3.2. UV–Vis absorption spectra The extinction coefficient of MakrofolÒDE1-1 in the UVB range of 302 nm shows that its photodegradation may be considered exclusively as a surface reaction limited to topmost few microns thick layer of the MakrofolÒDE 1-1 detector. Fig. 3. Presents the
A. Al-Amri et al. / Results in Physics 7 (2017) 1361–1366
Fig. 3. UV–Vis absorption spectra at different durations for pristine and UVB (302 nm)-irradiated MakrofolÒDE 1-1.
UV–Vis absorption spectra of the pristine and UVB (302 nm)–irradiated MakrofolÒDE 1-1 detector for different irradiation times [23,24]. There is a high absorbance band at shorter wavelength from 190 to 280 nm that is completely saturated with noise. This high absorbance, however, is attributed to a transition from a non-bonding orbital to p⁄ (n ? p⁄) and p ? p⁄ in C@O (Carbonyl group) and C@C. Staring from 280 nm at the absorption decreases sharply to 300 nm and the absorbance becomes almost constant from 300 nm to 450 nm and amounts to 0.8 ± 0.05. A new absorbance band is formed at about 310 nm, where the absorbance at this band increases with the increase in the irradiation time to UVB of 302 nm. This high absorbance, however, is attributed to a transition from a non-bonding orbital to p⁄ (n ? p⁄) and p ? p⁄ in C@O (Carbonyl group)and C@C [22]. Staring from 280 nm at the absorption decreases sharply to 300 nm and the absorbance becomes almost constant from 300 nm to 450 nm and amounts to 0.1 ± 0.5. As can be seen from Fig. 3 there exist a continuous red shift (shift towards longer wavelength in the UV–Vis spectra) by increasing the exposure time to ultraviolet radiation UVB (302 nm). The photochemistry of MakrofolÒDE 1-1 detector is strongly correlated with the spectral distribution of ultraviolet radiation either UVB of 302 nm either 365 nm. At wavelength of 302 nm mainly direct excitation of MakrofolÒDE 1-1 take place, beginning with the scission of the CO-O bond followed by two successive Photo-Fires rearrangements of aromatic carbonate group and leading to formation of phenylsalicylate and dihydroxybenzophenone units. However, the minor changes in UV–Vis spectra were elucidated by calculated the difference between the UVB (302) irradiated and pristine MakrofolÒDE 1-1. These difference spectra indicate the existence of a clear band at 280 nm and clear band at about 317 nm which increase with the increase in the irradiation time to UVB. As presented in Fig. 3. The formation of the band between 305 and 325 nm is assigned to the formation of a phenylsalicylate moiety that is formed by the first photo-Fires rearrangement. This is, however, is expected for UVB (302 nm) [23]. The second shoulder at about 350 nm attributed to the formation of dihydroxybenzophenone moiety, which is the second rearrangement step in the photo-Fries rearrangement, which is not observed by Diepens [11]. The regular shift in the absorption edge of UVB (302 nm)-irradiated MakrofolÒDE 1-1 reveals the reduction in the energy difference between HOMO-LUMO, which shows the possibility of tuning the optical properties of MakrofolÒDE 1-1 by exposure to UVB of 302 nm for different durations.
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The extinction coefficient of MakrofolÒDE 1-1 detector in the UVA range of 365 nm shows that its photodegradation may be considered exclusively as a bulk reaction spread over the all thickness of the MakrofolÒDE 1-1 detector, nevertheless, the ultraviolet radiation of 365 nm doesn’t absorbed by the MakrofolÒDE 1-1 detector since the absorbance at 365 nm amounts to 0.06 ± 0.02, which corresponding to attenuation coefficient of 5.6 cm1, as can be seen in Fig. 4. The influences of UVA of 365 nm irradiation for different duration on the MakrofolÒ DE 1-1 detector were monitored using UV–Vis spectrometer. On the UV–Vis exemplified in Fig. 4., which shows the absorbance of pristine and 400 h irradiated with UVA of 365 nm, no really significant changes were observed between pristine and 400 h irradiated MakrofolÒ DE 1-1. However, the results agree with the theoretical predication from the calculation of the attenuation coefficient as discussed above. Three wavelengths in the UV–Vis absorption spectra of 310, 350, and 550 have been selected to examine and characterize the correlation between the irradiation time (Dose) and the induced modifications in the UV–Vis absorption spectra of the MakrofolÒDE 1-1 detector are presented in Fig. 5. The absorbance of UVB (302 nm) irradiated MakrofolÒDE 1-1 detector at 310 and 350 nm
Fig. 4. UV–Vis absorption spectra at different durations for pristine and UVA (365 nm)-irradiated MakrofolÒDE 1-1.
Fig. 5. The absorbance band intensities versus the exposure time for the UVBirradiated MakrofolÒ DE 1-1 detector.
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is increased linearly for short irradiation time up to 35 h, the increment rate decreases with the increase in the exposure time getting saturated especially for extreme exposure time of 400 h. These results, however, confirm a formation a photo-stabilized groups on the irradiated surface of the MakrofolÒDE 1-1 detector, which hinder the further modification and the bulk MakrofolÒDE 1-1 detector. The parameterization of the absorbance at 310 nm as a function of the UVB (302 nm) irradiation time (Dose) can be carried out by fitting the data using the exponential growth function;
AbsðtExp: Þ ¼ 1:49 1:22Exp½0:019t Exp: :
ð1Þ
The parameterization of the absorbance at 350 nm as a function of the UVB (302 nm) irradiation time (Dose) can be carried out by the fitting using the exponential growth function;
AbsðtExp: Þ ¼ 1:08 0:97Exp½0:008t Exp:
ð2Þ
For the absorbance at 550 nm (in visible light region) of MakrofolÒ DE 1-1 detector, no significant changes in the absorbance were observed even for extreme exposure time of 400 h, the data are fitted using the a linear function
AbsðtExp: Þ ¼ 0:067 2 105 tExp:
Fig. 6. The indirect optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒDE 1-1 for different durations.
ð3Þ
The standard deviation is 0.43 and R equals to 0.12 and P amounts to 70%. The rate linear regression of the fitting line is about 0.00005, which indicates stability of the MakrofolÒ DE 1-1 detector in visible light region and no correlation at all between absorbance and irradiation dose at 550 nm in the absorption spectra. 3.3. Optical energy gaps UV–Vis spectroscopy can be applied to determine the modification in the optical properties of the MakrofolÒDE 1-1, including the determination of the inducedtransitions and for characterization the band structure and optical energy gaps. In principle, the optical absorption coefficient is correlated with energy of the incident electromagnetic radiation. The optical absorption coefficient (a) can be determined in terms of absorbance Abs(hm), which is measured by UV–Vis spectroscopy, and the thickness t measured in cm by [25]:
aðhmÞ ¼ 2:303
AbsðhmÞ t
ð4Þ
Fig. 7. The direct optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒDE 1-1 for different durations.
Meanwhile, the optical band gap (Eg) is correlated with optical absorption coefficient (a) and the photons energy (hm) the by Tauc’s expression [26],
aðhmÞ ¼
Cðhm Eg Þm ; hm
ð5Þ
where m characterizes the transition process in the K-space, which can assume the values 0.5, 1.5, 2, and 3 for direct allowed, direct forbidden, indirect allowed, and indirect forbidden, respectively [17]. C is known as band tailing parameter that amounts to C ¼ 4pr=ncEc where c is the speed of the light, r is the minimum conductivity, n is the refractive index, and Ec is the width of the trail states distribution. However, C correlates with the transition probability. The direct and indirect optical band gap energies are evaluated by plotting (ahm)2 and (ahm)0.5against the photon energy (hm). Considering the linear part of the fundamental absorption edge of the UV–Vis spectra, the best fit lines were employed to determine on the energy axis. Fig. 5. Presents the indirect optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒ DE 1-1 for different durations up to 400 h. There exists a continuous reduction in the optical band gap towards the lower energy. The indirect optical band gaps
Fig. 8. The dependence of natural logarithm of the absorption coefficient a on photon energy for a pristine and irradiated MakrofolÒDE 1-1 with UV wave of 302 nm wavelength.
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Table 1 Direct, indirect energy gaps, Urbach’s energy values, and the corresponding number of carbon atoms in the cluster (M) for MakrofolÒDE1-1 detectorirradiated with UVB of 365 nm for different durations. Exposure time [h]
Direct Eg [eV]
Indirect Eg[eV]
Eu[eV]
M direct
M Indirect
0 1 2 5 10 15 20 35 75 115 300 400
4.23 ± 0.02 4.21 ± 0.02 4.21 ± 0.02 4.19 ± 0.02 4.16 ± 0.02 4.14 ± 0.02 4.11 ± 0.02 4.07 ± 0.02 4.02 ± 0.02 4 ± 0.02 3.94 ± 0.02 3.90 ± 0.02
3.96 ± 0.02 3.87 ± 0.02 3.84 ± 0.02 3.82 ± 0.02 3.76 ± 0.02 3.68. ± 0.02 3.65 ± 0.02 3.59 ± 0.02 3.57 ± 0.02 3.52 ± 0.02 3.48 ± 0.02 3.45 ± 0.02
0.13 0.15 0.15 0.16 0.17 0.18 0.19 0.20 0.21 0.21 0.25 0.27
65 66 66 67 67 68 69 71 72 73 75 77
75 78 79 80 83 86 88 91 91 94 97 98
for different UVB (302 nm)-irradiation time decreases with the increase in the irradiation time. Fig. 7 shows the direct optical band gap of a pristine and the UVB (302 nm)-irradiated MakrofolÒ DE 1-1 for different durations up to 400 h. There exists a continuous reduction in the optical band gap towards the lower energy. The indirect optical band gaps for different UVCB (302 nm)-irradiation time decreases with the increase in the irradiation time. The values of the direct and indirect bands are summarized in Table 1 with their standard errors. Some characteristic aspects regarding the direct and indirect band gaps could be obtained from Table 1; these are: (1) observation of the coexistence of direct and indirect band gaps in UV (302)-irradiated MakrofolÒ DE 1-1, (2) the direct band gap is higher than the corresponding indirect band gap for UVB (302 nm)-irradiated MakrofolÒ DE 1-1, and (3) there was significant change in both direct and indirect band gaps, which suggested the possibility to use the MakrofolÒ DE 1-1 as UVB (302 nm) dosimeter. The energy gap Eg changes points to the formation of photochemical compounds between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy states. Urbach energy Eu, which is corresponding to the localized state width in the optical band gap, is related to the absorption coefficient and photon energy by the following equation [27]:
aðhmÞ ¼ a Exp
hm : Eu
ð6Þ
Here, ao is a constant and a(hm) is the absorption coefficient, Eu is the Urbach energy or the energy of the band tail. The Urbach energies are calculated by considering the inverse of the slop of the linear part of plotting curve of Ln [a(hm)] against (hm) as depicted in Fig. 6. The Urbach energies of pristine and UVB (302 nm) MakrofolÒ DE 1-1 for different durations are summarized in Table 1. One can observe that Urbach energy increases from 0.13 eV for pristine MakrofolÒ DE 1-1 detector and decreases to be around 0.27 eV at exposure time of 400 h (see Fig. 8). The energy of the optical band gaps depends on the number, type, and structural arrangement of the carbon bonds per molecule. Concerning the MakrofolÒ DE 1-1 as Bisphenol-A poly carbonate and considering Robertson’s relation that is reformulated by Fink [28], the number of the carbon atoms, M, per cluster is calculated using the following equation
34:3 Eg ¼ pffiffiffiffiffi M
ð7Þ
The values of carbon atoms per cluster in the pristine and UVB (302 nm) MakrofolÒ DE 1-1 are summarized in Table 1 for direct and indirect band gaps. The number of carbon atoms per cluster for direct band gap is found to increase as the irradiation time to
UVB of 302 nm from 65 for pristine to 77 for UVB irradiated MakrofolÒ DE 1-1 for 400 h for direct energy gap and from 75 for pristine to 98 for 400 h. However, according to the results summarized in Table 1, the UVB (302 nm) MakrofolÒ DE 1-1 detector is instable against UVB (302 nm) even for short exposure time. 4. Conclusion Throughout the current work, the induced modifications in the optical properties of MakrofolÒDE 1-1 solid state nuclear track detectors upon irradiation by UVB (302 nm) and UVA (365 nm) were characterized. Substantial red shifts in UV–Vis spectra and continuous increase in absorbance as the exposure time (Dose) to UVB increases were observed, meanwhile, there was insignificant change in the UV–Vis spectra of MakrofolÒDE 1-1 upon irradiation by UVA (365 nm), irrespective the irradiation time (dose). UVCirradiated MakrofolÒDE 1-1 exhibits absorption bands at 280 ± 5 nm and 315 ± 5 nm in UV–visible spectra, which are increasing exponentially as the irradiation time (dose) increase getting saturated at prolonged exposure times more than 35 h. The direct band gap is higher than indirect band gap and both decrease with the increase in the irradiation time of UVB of 302 nm. The Urbach energy and carbon atoms per cluster increase with the increase in the irradiation time. The induced modification in the optical properties of MakrofolÒDE 1-1 can be used in UVB dosimetry which it is not applicable for UVA of 365 nm. References [1] Durrani SA, Bull RK. Solid state nuclear track detection, principles, methods and applications. Pergamon Press; 1987. [2] Fleischer RL, Price PB, Walker RM. Nuclear tracks in solids: principles and applications. Berkeley: University of California Press; 1975. [3] Nikezic D, Yu KN. Mater Sci Eng 2004;46:51–123. [4] Pugliesi R, Pereira MA. Instrum Methods B 2002;484:613. [5] El Ghazaly M. Radiat Eff Defects Solids 2011;167:141. [6] Salamon MH, Price PB, Drach J. Nucl Instrum Methods Phys Res B 1986;17 (2):173. [7] Pugliesia F, Stanojev Pereira MA, Pugliesia R, Diasa MS. Appl Radiat Isot 2014;89:1. [8] Singh L, Samra KS. J Macromol Sci Part B Phys 2007;46:1041. [9] Fink D, Ghosh S, Klett R, Dwivedi KK, Kobayashi Y, Hirata K, Vacik J, Hnatowicz V, Cervena J, Chadderton LT. Nucl Instrum Methods Phys Res B 1998;146:486. [10] Wu T, Lee S, Chen W. Macromolecules 1995;28:5751. [11] Diepens M. Photodegradation and stability of bisphenol a polycarbonate in weathering conditions. Netherland: Eindhoven University of Technology; 2009. [12] Shah H, Rufus I, Hoyle C. Macromolecules 1994;27:553–61. [13] El Ghazaly M. Radiat Eff Def Solids 2012;167(2):141–8. [14] El Ghazaly M. Res Phys 2016;3:634–9. [15] Diffey BL. Rev Phys Med Biol 1991;36(3):299–328. [16] http://www.anilinkompaniet.se/img/folie/Makrofol-DE-1-1-ISO.pdf (access date 08.06.2014). [17] http://www.films.covestro.com/Products/Makrofol/ProductList.aspx (access date 09.07.2016). [18] https://www.uvp.com/elseries.html (access date 25.11.2016).
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[19] http://www.canon.com.cy/scanners/flatbed-scanners/canoscan_ 9000f_markii/ (access date 25.11.2016). [20] https://imagej.nih.gov/ij/(access date 25.11.2016). [21] http://www.labomed.com/Dual.htm (access date 22.06.2016). [22] Hareesh K, Pandey AK, Sangappa Y, Bhat Ravishankar, Venkataraman A, Sanjeev Ganesh. Nucl Instrum Methods B 2013;295:61–8. [23] Geretovszky Zs, Hopp B, Bertóti I, Boyd IW. Appl Surf Sci 2002;186:85–90.
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