Modifications in the optical and thermal properties of a CR-39 polymeric detector induced by high doses of γ-radiation

Author’s Accepted Manuscript Modifications in the optical and thermal properties of a CR-39 polymeric detector induced by high doses of γ-radiation A.F. Saad, Mona H. Ibraheim, Aya M. Nwara, S.A. Kandil www.elsevier.com/locate/radphyschem

PII: DOI: Reference:

S0969-806X(17)30615-1 https://doi.org/10.1016/j.radphyschem.2017.10.011 RPC7670

To appear in: Radiation Physics and Chemistry Received date: 12 June 2017 Revised date: 16 September 2017 Accepted date: 15 October 2017 Cite this article as: A.F. Saad, Mona H. Ibraheim, Aya M. Nwara and S.A. Kandil, Modifications in the optical and thermal properties of a CR-39 polymeric detector induced by high doses of γ-radiation, Radiation Physics and Chemistry, https://doi.org/10.1016/j.radphyschem.2017.10.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Modifications in the optical and thermal properties of a CR-39 polymeric detector induced by high doses of γ-radiation A.F. Saad1, *, Mona H. Ibraheim 1, Aya M. Nwara1, S.A. Kandil 2 1

Physics Department, Faculty of Science, Zagazig University, Zagazig, Egypt

2

Cyclotron Project, Nuclear Research Centre, Atomic Energy Authority, B.O. 13759, Cairo Egypt

Abstract

Effects of γ-radiation on the optical and thermal properties of a poly allyl diglycol carbonate (PADC), a form of CR-39, polymer have been investigated. CR-39 detectors were exposed to γ-rays at very high doses ranging from 5.0×105 to 3.0×106 Gy. The induced changes were analyzed using ultraviolet-visible spectroscopy (UV-VIS) in absorbance mode, and thermogravimetric analysis (TGA). The UV-visible spectra of the virgin and γ-irradiated CR-39 polymer detectors displayed a significant decreasing trend in their optical energy band gaps for indirect transitions, whereas for the direct ones showed a little change. This drop in the energy band gap with increasing dose is discussed on the basis of the gamma irradiation induced modifications in the CR-39 polymeric detector. The TGA thermograms show that the weight loss rate increased with increase in dose, which may be due to the disordered system via scission followed by crosslinking in the irradiated polymer detector. The TGA thermograms also indicated that the CR-39 detector decomposed in three/four stages for the virgin and irradiated samples. The activation energy for thermal decomposition was determined using a type of Arrhenius equation based on the TGA experimental results. These experimental results so obtained can be well used in radiation dosimetry.

Key Words: CR-39; γ -radiation; UV-Vis; TGA; radiation dosimetry * Corresponding author. Tel.: +20 55 2303252; Fax: +20 55 2308213, Mobile: +20 1016746496;1225307497 E-mail address:[email protected] (A.F. Saad).

1. Introduction Poly allyl diglycol carbonate (PADC), a form of CR-39, polymer is one of the most sensitive solid state nuclear track detectors (SSNTDs) widely used for radiation detection (Cartwright et al., 1978; Cassou and Benton, 1978). CR-39 is also widely used in various fields such as neutron dosimetry, high energy interactions and cosmic ray, environmental radioactivity, complex radioactivity and many other fields in particle and nuclear physics (Price, 2005, 2008 ). CR-39 polymeric detector is transparent in visible spectrum and almost totally opaque in spectroscopic range. Thus, it is desirable because of its constructive uses as mentioned above and also for its good sensitivity, uniformity, and high degree of optical transparency. In CR-39 detectors, only those charged particles with high linear energy transfer (LET) can create radiation damage trails, or tracks. Radiations such as UV rays and X-rays, gamma rays are low LET radiations, those photons cannot create any tracks, but can affect etch rate values of detectors depending upon the exposure dose of photons. Radiation, in the form of swift heavy ions, neutrons, X-rays and gamma rays, can play a significant role in modification of physical, structural, chemical, optical, and electrical properties of polymeric materials (Marletta, 1990; Calcagno et al., 1992; Steckenreiter et al., 1997; Saha et al., 2000; Zhu et al., 2000; Srivastava et al., 2002; Phukan et al., 2003; Khan et al., 2005; Kumar et al., 2011; Singh and Prasher, 2005; Raghuvanshi et al., 2012). These modifications are caused by chain scission, bond breaking, free radical formation and creation of unsaturated bonds followed by

intermolecular cross-linking subsequently producing a new various complex chemical compounds. (Akber et al., 1980; Chong et al., 1997; Malek and Chong, 2000, 2002; Saad et al., 2001; Yamauchi, 2003). Several works have been carried out on low and medium doses of gamma-induced changes in polymers (Saad et al., 2005; Sharma et al., 2007; Saad et al., 20014a). In fact, radiation damage processes induced by high doses of gamma ray might be different from those triggered by low doses. Consequently, in the current paper, our motivation was aimed to study these changes in CR-39 detector induced by γ-ray at high doses ranging from 5×105 to 3×106 Gy. For this purpose, two standard techniques of ultraviolet-visible spectroscopy (UV-VIS) in absorbance mode, and thermogravimetric analysis (TGA) of material investigation are used. 2. Theoretical considerations 2.1 Calculations of optical properties The absorption coefficient a (hn ) can be calculated from the absorbance ( A) by using the following formula (Fox, 2001)

a (hn ) = A l

(1)

where l is the sample thickness in cm and A is defined as A = log( I o I ) , where I o and I are the intensity of the incident and transmitted UV-VIS beams, respectively. The absorption coefficient is very small below the band edge in insulators and follows the Urbach relation (Urbach, 1953)

a (hn ) = a o exp (hn Eu )

(2)

where a (hn ) is the absorption coefficient, which is a function of photon energy hn . a o is a constant and Eu , Urbach’s energy, is equal to the inverse logarithmic slope of the absorption coefficient. To determine the optical band gap energy, eq. (2) has been adapted to a more general form by Mott and Davis (1979)

a (hn ) = B(hn - Eg )n hn

(3)

where hn is the energy of the incident photons, the factor B depends on the transition probability and can be assumed to be constant within the optical frequency range, and E g is the value of the gap energy between the valence band and the conduction band and n is the power, which characterizes the electronic transition, whether it is direct or indirect during the absorption process in K-space. Specifically, n is 2, 3, 1/2 and 3/2 for indirect allowed, indirect forbidden, direct allowed and direct forbidden transitions, respectively. In the case of the direct energy band gap, the optical transition due to excitation of electrons between the lower band and upper band takes place directly, whereas in the indirect one the relative positions of the conduction band and valence band do not match and the transition involves phonons in order to conserve momentum. The phonon energy e can be calculated from the energy difference between the optical band gap energy transitions (direct, E gd , and indirect,

E gind ) using the following formula (Saad et al., 2014b):

e = E gd - E gind

(4)

The number of carbon atoms per conjugation length N for a linear structure (Fink et al., 1995) is given by

N = 2bp E g

(5)

where N is the number of carbon atoms per conjugated length and 2b gives the band structure energy of a pair of adjacent p sites. The value of β is taken to be - 2.9eV as this is associated with the p ® p * optical transition in the - C = C - structure. 2.1 Calculations of activation energy based on TGA results The activation energy Ea stands to the energy needed to activate the molecules constituting the physical system to undergo a phase transition. Consequently, it must be measured to assess the thermal stability of a heat-resisting polymer material. Based on Arrhenius equation, the dependence of normalized weight loss on temperature can be reformed (Saad et al., 2014a): =

(6)

where mo and Δm are the initial weight at room temperature and the weight loss at temperature

of the CR-39 sample, respectively;

and

are the heights of the

initial weight and weight loss on a plot of the thermogram, which actually represent mo and Δm, respectively; plot of ln

against 103/

is a fitting parameter and k is the Boltzmann constant. A will produce a straight line of slope

activation energy of the physical system.

3. Experimental procedure

, Ea is the

Poly allyl diglycol carbonate (PADC), a form of CR-39, high polymer based nuclear track detectors (NTDs) sheets of TASTRAK were produced and provided by Track Analysis Systems Ltd. (TASL), Bristol, UK. A standard thickness of 750 µm was used. The polymeric detector samples were cut to a size of 2×3 cm2. The detector samples were irradiated by the 60Co gamma cell irradiation facility of type MC-20 fabricated by the Russian Atomic Energy. The dose rate was 1.2 kGy/h. The detector samples were positioned at the centre of the driving belt and the irradiation process was achieved automatically. The detector samples were irradiated at different gamma doses ranging from 5×105 to 3×106 Gy. The samples were irradiated for various times in order to maintain the various doses. These irradiations were performed at the Gamma Division, Atomic Energy Authority, Cairo. The UV-Visible spectrophotometer Model (Spectro UV-Vis 2800, USA) was operated in spectrum mode (ABS mode) at a scanning speed of 25 nm/min. The working wave length range of the spectrometer is 190–1100 nm. The instrument is specified by wavelength accuracy ± 0.30 nm at a variable spectral bandwidth ( of 5, 2, 1, and 0.5 nm) in the UV/VIS region. Thermo gravimetric analyzer, Shimadzu TGA-50, made in Japan, was operated at heating rate 10 ºC min-1 and cooled by nitrogen gas with rate 20 mL min-1.

4. Results and discussion 4.1 UV-visible spectroscopy The optical absorption measurements with UV-visible spectrophotometer carried out in the wavelength range from 190 to 1100 nm at room temperature on the virgin and irradiated CR-39 detector samples are shown in Fig.1. The absorption peak shifts from the UV region towards the visible region, i.e., towards the higher wavelength, for the irradiated

samples. The samples become gradually opaque to the visible light and the material of these films changes from very high transparent to yellowish with the increase of the gamma dose. From a systematic study of the spectral behavior of the exposed samples as a function of γray dose, the wavelength values of UV-visible light transmitted through the exposed samples compared with that of the virgin sample at selected absorbance values of 0.5, 1.0, 1.5 and 2.0 (arbitrary unit) are plotted as a function of the exposure dose, as shown in Fig. 2. The UV spectral technique was tested on the unidentified doses in NTDs gamma dosimetry by using a standard exposure. In this figure, we will show an example of the application of UV spectral technique by using CR-39 irradiated with an unknown dose of γ-radiation. This unknown dose was found to be about 765 kGy as shown in Fig. 2. The uncertainty in the unknown dose was found to be about 4.38 % deviation from the actual dose of 800 kGy. The results show that the unknown γ-dose can be rapidly estimated. The logarithm of the absorption coefficient a (hn ) as a function of the photon energy

(hn ) for the virgin and irradiated CR-39 polymer detectors are plotted in Fig. 3. The values of the Urbach energy (Eu ) are calculated by taking the reciprocal of the slopes of the linear portion in the lower photon energy region of these curves and are enlisted in Table 1. The results show that the Eu values increase as the γ-ray dose increases and this may be attributed to the enhancement of chain scission in the irradiated CR-39 detectors, whereas the highest dose shows an opposite behavior. From the UV-visible absorption spectra, the band gap of the virgin and irradiated CR1n

39 polymer detectors was calculated by extrapolation of the plot of (ahn ) versus (hn ) on

12

the hn axes. For the determination of indirect and direct energy band gap, (ahn )

and

(ahn )2 , respectively, were plotted as a function of photon energy (hn ) , taking into account the linear portion of the fundamental absorption edge of the UV-Visible spectra, as shown in Fig. 1. These plots are presented in Figs. 4 and 5, respectively. From the intercept of the fit lines on the hv axis as depicted in Figs. 4 and 5, the indirect and direct band gaps have been determined for pristine and γ-irradiated CR-39 polymer detectors with different doses. The results are presented in Table 1. It can be seen that the band gap for the PADC film based NTDs decreases from 3.51 to 2.59 and 3.87 to 3.41 eV for indirect and direct transitions, respectively, as a result of γ-ray irradiation. The results show that the optical band-gap values decrease as the γ-ray dose increases. Thus, we can say that our present study proves that the optical band gap energies of CR-39 is rather dependent on the gamma dose. This is somewhat consistent with published data for gamma irradiation (Sinha et al., 2001), although our results show that the optical band-gap was gradually reduced with gamma dose and reached a minimum of 2.59 eV for the CR-39 (TASTRACK) irradiated by a dose of 2500 kGy, while it shows further dependence on gamma dose in the case of CR-39 (American Acrylics) and reached a minimum of 2.46 eV at a dose of 1000 kGy (106 Gy) as reported (Sinha et al., 2001). It should be noted that gamma radiation damage process induced by high dose of 2500 kGy, as observed in the current study, might be no different from those triggered by low dose of 1000 kGy as recorded (Sinha et al., 2001). This may be because the polymerization conditions of the detector material of both kinds of CR-39 detectors, CR-39 (TASTRAK) and CR-39 (American Acrylics), were different. The variation of optical band gap with γ-ray irradiation can be explained as the drastic chain scissions followed by the cross-linking

process which gives a high degree of disorder due to the fact that γ-rays create along their path a region of damage

produced by three processes, physical, physico-chemical and

chemical (Durrani and Bull, 1987). The results of the number of carbon atom (N ) values per conjugation length, known as a cluster, are enlisted in Table 1. It can be seen that the number of carbon atoms (N) per conjugation length in the case of direct transitions remains constant, i.e., N = 5 carbon atoms in a cluster for pristine and irradiated CR-39 detectors for all doses, as shown in Table 1. While, in the case of indirect transitions, N per conjugation length increases non-linearly with γ-rays dose. From 0 to 500 kGy, there is a considerable increase in N to 6 atoms per conjugation length and this remains constant thereafter up to the dose of 1500 kGy. From 1500 to 2000 kGy, there is another significant increase in N to 7 atoms per conjugation length, and this also remains constant thereafter up to the end of the irradiation dose at 3000 kGy. It is very interesting to note that the number of carbon atoms (N) in a cluster in the direct transition case does not change over the entire irradiation dose, while in the indirect transition case, the number of carbon atoms gradually and systematically increased over three stages. This behavior is attributed to the significant decline in the band gap, indirect transitions, cause a considerable increase in the number of carbon atoms N while the direct one shows an insignificant change which reflects a null change in this number N (Saad et al., 2015). 4.2 TGA study CR-39 polymeric detectors exposed to different doses of γ-rays were heated from about 30 ºC to around 700 ºC and the progressive weight losses were recorded.

Fig. 6 compares the thermograms of virgin and γ-ray-irradiated CR-39 detectors, showing the weight loss (%) as a function of temperature. The temperatures Tend (ºC) corresponding to the start of decomposition and the four decomposition zones, major, minor, a formed zone produced by γ-rays, and residual, are summarized in Table 2. The temperature at which the mass change reaches a magnitude that the thermobalance can detect was taken as the onset of decomposition temperature, and was found to be about 143 ºC for the virgin CR-39 sample. It was observed to be significantly raised in the irradiated sample, measured as about 222 for the CR-39 detector exposed to 500 kGy of γ-rays. It was also observed to be somewhat raised in the other irradiated samples, measured as about 167, and 163 ºC for the CR-39 detectors exposed to 1000, and 1500 kGy of γ-rays, respectively, while for the other two detector samples exposed to 2500 and 3000 kGy showed a little bit decrease compared to the virgin one. However, the sample exposed to 2000 kGy noticeably showed the opposite effect, its onset of decomposition temperature being just 135 ºC. Fig. 6a shows that in the case of no gamma dose the polymer detector underwent a weight loss of 66.35 % at around 383 ºC followed by a further 21.81 % at around 441 ºC, and that 11.84 % weight remained at the end of the temperature range. The detectors exposed to γ-ray doses of 500, 1000, 1500, 2000, 2500, and 3000 kGy underwent weight losses of 65.0, 62.04, 44.98, 59.10, 60.06, and 60.38 % at around 384, 383, 382, 367, 375, and 364 ºC, respectively, followed by a further 28.47, 24.98, 17.20, 25.69, 26.52 and 30.12 % at around 337, 445, 440, 447, 450 and 450 ºC, respectively, and residues of 6.53, 12.98, 37.82, 15.21, 9.07, and 9.50 % remained at the end of the temperature range, as indicated in Table 2. Fig. 6a also shows that in

the case of gamma dose of 2500 kGy the polymer detector underwent a weight loss of 4.35 % at around 464 ºC as a decomposition of new chemical products induced by gamma rays named as a third unstable zone, as also indicated in Table 2. Fig. 6b shows that in the case of gamma dose of 1500 kGy the polymer detector underwent abnormal increase in the thermal stability compared to the virgin sample and the other irradiated ones. It should be mentioned that there was an irregular decrease in thermal stability of the irradiated CR-39 samples, while the dose of 1500 kGy generally show opposite trend. The change in thermal stability of the irradiated CR-39 detectors may be attributed to the production of some chromophoric groups and /or scattering due to new complex compounds formed. Fig. 7 shows the first derivative decomposition curves obtained for the virgin and γ-ray-irradiated CR-39 detectors. For the virgin detector, the first and second Tmax peaks were located at 362 and 435 ºC, respectively. For the irradiated CR-39 detector samples, however, a new derivative peak induced by the γ-rays was observed, in addition to the aforementioned two typical decomposition peaks. The results are summarized in Table 3. It should be noted that for the decomposition zone induced by γ-rays, Tmax was found to have 410 and 506 ºC for doses of 500 and 2500 kGy, respectively, whereas for the other doses no induced-peaks were measured. However, the Tmax values of the characteristic decomposition zones, major and minor, were found to remain at around 355 and 442, 357 and 437, 357 and 434, 343 and 439, 348 and 439, and, 348 and 442 ºC, respectively, in the irradiated CR-39 detectors for doses 500, 1000, 1500, 2000, 2500 and 3000 kGy, respectively, as reported in

Table 3. It is clear that there was a significant change in the CR-39 detector material induced by γ-rays with respect to the thermal properties of the virgin polymer. It is very interesting to note that the thermal stability of a CR-39 detector exposed to doses of 1500 and 2500 kGy of γ-rays was considerably altered, the first dose is in increase while the other one is in decrease. The CR-39 detector must have undergone a significant degree of scission of its long-chain molecules, converting them into shorter fragments, as a result of the γ-ray exposure. Indeed, the CR-39 detector became permanently softened, resulting in an increase in the total mass loss and a decrease in the thermal stability and thermo balance thresholds at certain γ-ray doses, except the detector exposed to a dose of 1500 kGy show opposite trend. Fig. 8 shows plots of ln Δm/mo versus 1/T (1000/k) for the virgin CR-39 detector and CR-39 detectors exposed to different doses of γ-rays ranging from 500 to 3000 kGy. Using a least-squares fitting method, the activation energies of thermal decomposition in the CR-39 detectors were deduced from the slopes of the straight lines in Fig. 8. The activation energies of the CR-39 detectors irradiated with different doses of γ-rays are composed in Table 4. The activation energy of the first-order decomposition increases at a dose of 500 kGy, then regularly decreases with increasing gamma dose up to 2000 kGy, but once again increases at 2500 kGy and then decreases at the end of dose range, making the CR-39 polymer more susceptible to thermal decomposition. For the second-order decomposition, however, irradiation was observed to have more or less the same effect.

5. Conclusion

The data analysis of the UV–visible spectra and TGA thermograms of the virgin and γ-irradiated CR-39 polymeric detector led to the following conclusions: ·

Gamma-ray irradiation had a considerable effect on the optical band gap energy, and direct and indirect transitions, of the irradiated CR-39 detectors. Decreases of 23.9 and 10.6 % were observed in the energy band gaps for the virgin CR-39 detector and the γ-irradiated CR-39 detectors, from 3.51 and 3.87 eV to 2.67 and 3.46 eV, respectively, for indirect and direct transitions. Very large increases of 127.8 and 130.4 % were observed in the phonon energy and Urbach energy for the virgin detector and the irradiated detector with dose of 2500 kGy, from 0.36 and 0.23 eV to 0.82 and 0.53 eV, respectively. Also, increases of 40 % in the number of carbon atoms (N) per conjugated length from 5 to 7 for the virgin detector and the irradiated detectors in the indirect transition, while that number of carbon atoms remains constant at 5 in the direct transition.

·

The TGA thermograms indicated a significant degradation of the polymer chain under gamma irradiation, making the material more vulnerable to decomposition than a virgin detector, while a CR-39 detector exposed to 1500 kGy shows opposite trend .

·

Analysis of weight-loss derivative data showed a clearly discernible effect on the thermal stability, which was most prominent at a dose of 2500 kGy. An increase in the weight-loss derivative of the CR-39 detector by this dose further enhances the potential usable range of this polymer in high-temperature applications.

·

The first- and second-order activation energies of thermal decomposition of a CR-39 detector are more or less similarly affected by g-irradiation. The activation energies were greatened by around 7 and 14 % at a dose of 500 kGy and were lowered by

around 14 % at a dose of 2000 kGy for the first and second-order processes, respectively. ·

UV-VIS and TGA observations suggested that the CR-39 polymer detector enabled an estimated gamma radiation dose to be determined.

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Fox, Mark, 2001. Optical Properties of Solids. Oxford University Press Inc., New York. Kumar, V., Sonkawade, R.G., Chakarvarti, S.K., Kulriya, P., Kant, K., Singh, N.L., Dhaliwal, A.S., 2011. Study of optical, structural and chemical properties of neutron irradiated PADC film. Vacuum 86, 275–279. Malek, M.A., Chong, C.S., 2000. FTIR study of H2O in poly allyl diglycol carbonate. Vib. Spectrosc. 24, 181–184. Malek, M.A., Chong, C.S., 2002. Generation of CO2 in γ-ray irradiated CR-39 plastic. Radiat. Meas. 35, 109–112. Marletta, G., 1990. Chemical reactions and physical property modifications induced by keV ion beams in polymers. Nucl. Instrum. Methods Phys. Res. B 46, 295–305. Mott, N.F., Davies, E.A., 1979. Electronic Processes in Non-Crystalline Materials. Clarendon Press, Oxford. Phukan, T., Kanjilal, D., Goswami, T.D., Das, H.L., 2003. Study of optical properties of swift heavy ion irradiated PADC polymer. Radiat. Meas. 36, 611–614. Raghuvanshi, S.K., Ahmad, B., Siddhartha, Srivastava, A.K., Krishna, J.B.M., Wahab, M.A., 2012. Effect of gamma irradiation on the optical properties of UHMWPE (ultra-highmolecular-weight-polyethylene) polymer. Nucl. Instrum. Methods Phys. Res. B 271, 44–47.

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Figure's Captions Fig. 1. UV–visible spectra of the virgin and γ-ray-exposed CR-39 polymer

detectors

for different doses ranging from 500 to 3000 kGy. Fig. 2. Plots of wavelength of UV-visible light transmitted through the virgin and γray-exposed CR-39 detectors at absorbance values of 0.5, 1, 1.5 and 2

(arbitrary

unit) with exposure dose. Fig. 3. Logarithmic variation of the absorption coefficient a (hn ) as a function of photon energy (hn ) , for the virgin and irradiated CR-39 detectors exposed to different doses. The solid linear lines stand for the fitting lines of curves to the energy axis (hn ) . The values of the the reciprocal of the slopes of theses linear lines.

γ-rays

with

the straight parts of the

Urbach energy are determined by taking

Fig.4. Plots for indirect band gap (eV) in virgin and irradiated CR-39 detectors γ-rays with different doses. The solid linear lines stand for the parts of the curves to the energy axis (hn ) . The the energy axis (hn ) yields the

fitting lines of the straight

extrapolation of these solid linear lines to

indirect band gaps.

Fig. 5. Plots for direct band gap (eV) in virgin and irradiated CR-39 detectors γ-rays with different doses. The solid linear lines stand for the parts of the curves to the energy axis (hn ) . The the energy axis (hn ) yields the direct

exposed to

exposed to

fitting lines of the straight

extrapolation of these solid linear lines to

band gaps.

Fig. 6. TGA thermograms of a virgin CR-39 detector and detectors irradiated with γrays at different doses up to 3000 kGy (a) stacked thermograms and (b)

composed

thermograms.

Fig. 7. Weight-loss derivative curves of a virgin CR-39 detector and detectors with γ-rays at different doses up to 3000 kGy (a) stacked

irradiated

thermograms and (b) composed

thermograms.

Fig.8. Plot of the logarithm of normalized weight loss as a function of inverse temperature 1/T at different doses ranging from 500 to 3000 kGy (a) first order (b) second-order decompositions.

and

Table 1

γ-ray dose

( kGy ) 0 500 1000 1500 2000 2500 3000

Band gap energy (eV) Indirect Direct 3.51 3.30 3.11 3.00 2.80 2.59 2.67

Phonon energy (eV)

3.87 3.74 3.64 3.55 3.49 3.41 3.46

Urbach energy (eV)

0.36 0.44 0.53 0.55 0.69 0.82 0.79

0.23 0.30 0.34 0.36 0.43 0.53 0.43

Carbon atoms (N) in a cluster Indirect Direct 5 6 6 6 7 7 7

5 5 5 5 5 5 5

Optical band gap energy, phonon energy, Urbach energy, and carbon atoms (N) in a cluster of PADC polymer-based NTDs exposed to γ-rays with different high doses.

Table 2 Temperatures corresponding to the percentage weight losses at the end of the stable zone and the thermal decomposition zones, Tend (⁰C), of PADC-based CR-39 NTDs exposed to different doses of γ-rays.

Gamma dose (kGy)

Tend(⁰C)/percentage weight loss Stable zone

1st unstable 2nd unstable 3rd unstable 4th unstable zone: zone: zone: zone:* residual major minor Decomposition decomposition decomposition decomposition of new zone 383/66.35 441/21.81 700/11.84

0

143/ ̴0

500

222/ ̴0

384/65.00

337/28.47

700/6.53

1000

167/ ̴0

383/62.04

445/24.98

700/12.98

1500

163/ ̴0

382/44.98

440/17.20

700/37.82

2000

135/ ̴0

367/59.10

447/25.69

2500

140/ ̴0

375/60.06

450/26.52

3000

142/ ̴0

364/60.38

450/30.12

700/15.21 464/4.35

700/9.07 700/9.50

* Decomposition of new chemical products zone induced by gamma rays.

Table 3 Temperatures of maximum mass loss rate Tmax (⁰C) in the thermal decomposition of PADCbased CR-39 NTDs irradiated with different doses of γ-rays.

Gamma dose (kGy)

Tmax (⁰C) Characteristic major zone

Characteristic minor zone

0

362

435

500

355

442

1000

357

437

1500

357

434

2000

343

439

2500

348

439

3000

348

442

γ-ray-induced new zone 410

506

Table 4 Activation energies Ea (eV) for the thermal decomposition of CR-39 detector irradiated with different doses of γ-rays.

Gamma dose (kGy)

Activation energy (eV)

1st order 0.57 0.61 0.57 0.55 0.49 0.53 0.50

0 500 1000 1500 2000 2500 3000

2ndorder 0.21 0.24 0.22 0.23 0.18 0.21 0.18

3rd order

0.07

Highlights γ-ray irradiation has been proposed to study CR-39 based NTDs. The effect of wide range of high doses on CR-39 detectors was investigated. Optical and thermal properties of virgin and irradiated CR-39 detectors were studied. The UV spectral results show that the unknown γ-dose can be rapidly estimated. Effectiveness of different irradiation doses against thermal stability was determined. Dose of 2500 kGy was established as sufficient for highly degradation in CR-39.

3.5

3.0

0KGy 500KGy 1000KGy 1500KGy 2000KGy 2500KGy 3000KGy

2.5

Absorbance

· · · · · ·

2.0

1.5

1.0

0.5

0.0 200

400

600

Wavelength (nm)

800

1000

Fig. 1

475

absorbance 0.5 absorbance 1.0 absorbance 1.5 absorbance 2.0

450

Wavelength (nm)

425

400

Unknown Dose

375

350

325

300 0

500

1000

1500

Dose (kGy)

2000

2500

3000

Fig. 2.

5

0 kGy 500 kGy 1000 kGy 1500 kGy 2000 kGy 2500 kGy 3000 kGy

3

-1

Ln a (cm )

4

2

1

0 0

1

2

3

4

5

hv (ev)

Fig. 3

6

7

7

0 KGy 500 KGy 1000 KGy 1500 KGy 2000 KGy 2500 KGy 3000 KGy

6

4

3

a

1/2

(cm

-1/2

)

5

2

1

0 0

1

2

3

4

hv (ev)

Fig. 4.

5

6

7

.

1800

0 kGy 500 kGy 1000 kGy 1500 kGy 2000 kGy 2500 kGy 3000 kGy

1600 1400

2

a (cm

-2

)

1200 1000 800 600 400 200

. 0 0

1

2

3

4

hv (ev) Fig. 5.

5

6

7

100

3000 kGy

Weight loss %

-1.271 mg -60.380 %

Fig.6.

50

100

0 kGy 500 kGy 1000 kGy 1500 kGy 2000 kGy 2500 kGy 3000 kGy

-0.634 mg -30.119 %

2500 kGy

Weight loss %

-1.257 mg -60.057 %

50

Weight loss %

0 100

50

-0.555 mg -26.517 %

-0.091 mg -4.348 % 0 100

2000 kGy

Weight loss %

-0.436 mg -25.692 %

100 0

1500 kGy

Weight loss %

-1.007 mg -44.975 %

-0.385 mg -17.195 %

0 100

Weight loss %

1000 kGy

-1.500 mg -62.035 % 50

-0.604 mg -24.979 %

0 100

500 kGy

Weight loss %

-1.055 mg -65.003 %

50

-0.462 mg -28.466 %

0 100

Weight loss %

0 kGy

-1.518 mg -66.346 % 50

-0.499 mg -21.809 %

0 0

200

400

Temperature (°C)

200

400

Temperature (°C)

50

50

0 0

-1.003 mg -59.104 %

600

600

0.002

3000 kGy 0.001

Arbitrary unit

0.000

-0.001

Fig. 7. 0.002

-0.002

-0.003

0.001 -0.004 0.002

2500 kGy

0.000

Arbitrary unit

0.000

Arbitrary unit

0.001

-0.001

0 kGy 500 kGy 1000 kGy 1500 kGy 2000 kGy 2500 kGy 3000 kGy

-0.001

-0.002 -0.002

-0.003

-0.003

-0.004 0.002

2000 kGy

-0.004 0

0.001

100

200

300

400

Temperature (°C)

Arbitrary unit

0.000

-0.001

-0.002

-0.003

-0.004 0.002

1500 kGy 0.001

Arbitrary unit

0.000

-0.001

-0.002

-0.003

-0.004 0.002

1000 kGy 0.001

Arbitrary unit

0.000

-0.001

-0.002

-0.003

-0.004

0.002

500 kGy 0.001

Arbitrary unit

0.000

-0.001

-0.002

-0.003

-0.004

0.002

0 kGy 0.001

Arbitrary unit

0.000

-0.001

-0.002

-0.003

-0.004 0

100

200

300

400

Temperature (°C)

500

600

700

500

600

700

-1

1000/T (K )

a)

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

0

0 kGy 500 kGy 1000 kGy 1500 kGy 2000 kGy 2500 kGy 3000 kGy

-1

ln (Dm/mo)

-2

-3

-4

-5

-6

b)

-1

1000/T (K ) 1.30 0.1

1.35

1.40

1.45

1.55

1.60

1.65

0 kGy 500 kGy 1000 kGy 1500 kGy 2000 kGy 2500 kGy 3000 kGy

0.0 -0.1 -0.2

ln (Dm/mo)

1.50

-0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9

Fig. 8.