Nuclear Instruments and Methods in Physics Research B 325 (2014) 79–83

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Nuclear Instruments and Methods in Physics Research B

journal homepage: www.elsevier .com/locate /n imb

Changes in the thermal properties of PADC film-based nuclear trackdetectors produced by high doses of c-radiation

http://dx.doi.org/10.1016/j.nimb.2014.02.0060168-583X/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author at: Physics Department, Faculty of Science, ZagazigUniversity, 44519 Zagazig, Egypt. Tel.: +20 55 2303252; mobile: +20 1016746496;1225307497; fax: +20 55 2308213.

E-mail address: abdallahsaad56@hotmail.com (A.F. Saad).

A.F. Saad a,b,⇑, Noura Saad b, Y.K. Abdalla b

a Physics Department, Faculty of Science, Zagazig University, 44519 Zagazig, Egyptb Physics Department, Faculty of Science, University of Benghazi, 9480 Benghazi, Libya

a r t i c l e i n f o a b s t r a c t

Article history:Received 23 October 2013Received in revised form 17 January 2014Available online 9 March 2014

Keywords:PADC filmHigh gamma dosesThermogravimetric analysis (TGA)Activation energy

Irradiation effects on the thermal properties of poly allyl diglycol carbonate (PADC) polymer-basednuclear track detectors (in the form of CR-39) have been investigated. PADC films were exposed to c-raysat high doses ranging from 5.0 � 105 to 1.0 � 106 Gy. The induced modifications were analyzed by meansof thermogravimetric analysis, which indicated that the PADC film decomposed in three main stages. Theactivation energy for thermal decomposition was determined using a type of Arrhenius equation basedon the TGA experimental results. This study presents quantitative results showing that the exposed PADCfilms do not undergo continual further degradation from high-energy c-photons with increase in dose.The experimental results also provide insight into the specific property changes induced by c-rays, whichmay be of use for industrial applications.

� 2014 Elsevier B.V. All rights reserved.

1. Introduction [5,20–27]. Although much work has been carried out on the

Radiation plays an important role in modification of thephysical, chemical, structural, electrical, mechanical, and opticalproperties of polymer-based nuclear track detectors (NTDs) [1–10].Ionizing particles passing through solid matter deposit energyin the detector material and cause damage trails along their trajec-tories, known as latent tracks. These damage trails are irreversiblechanges in the macromolecular structure of the detector material[11–13]. As c-rays pass through matter, photons interact withatoms. The type of interaction is a function of the energy of thephotons and the atomic numbers of the elements that constitutethe matter. As a result of the interactions between photons andatoms, the intensity of the photon beam decreases as the beampasses through matter. The energy imparted by the incidentphotons induces changes in the polymer film, such as chainscission, bond breaking, creation of unsaturated bonds, and lossof volatile fragments, which may be followed by intermolecularcross-linking to produce various new complex chemicalcompounds [5,14–19]. The modifications induced in polymers byionizing radiation constitute one of the most important field inradiation physics, and there is much on-going effort to explorefurther radiation-induced modifications in polymer films

changes in polymers induced by low and high doses of c-radiation[5,8,28], research on the effects induced by very high doses hasreceived a great deal of attention [9]. In the present study, we haveexamined the modifications in PADC polymer-based NTDs inducedby c-rays at doses, ranging from 5 � 105 to 1 � 106 Gy, higher thanthat those presented in our previous study [5], using the thermo-gravimetric analysis (TGA).

2. Thermal decomposition model

We propose a simple model based on a type of Arrhenius equa-tion to determine the activation energy of thermal decompositionin PADC film-based NTDs. This model of thermal decompositionhas been proposed to describe the thermal stability kinetics as afunction of temperature at a constant rate. The dependence ofnormalized weight loss on temperature can be expressed by a typeof Arrhenius equation:

Dm=m0 ¼hh0¼ A exp � Ea

kT

� �ð1Þ

where m0 and Dm are the initial weight at room temperature andthe weight loss at temperature T of the PADC sample, respectively;h0 and h are the heights of the initial weight and weight loss on aplot of the thermogram, which actually represent m0 and Dm,respectively; A is a fitting parameter and k is the Boltzmannconstant. A plot of ln h=h0 against 103/T will produce a straight lineof slope �Ea=kT .

80 A.F. Saad et al. / Nuclear Instruments and Methods in Physics Research B 325 (2014) 79–83

3. Experimental procedure

Poly allyl diglycol carbonate (PADC) polymer-based nucleartrack detectors (NTDs) manufactured by Intercast Europe Co. ofParma, Italy, in the form of sheets of uniform thickness 660 lmof size 2 � 2 cm 2, were used in this investigation. The films wereirradiated in a 60Co gamma cell irradiation facility (ISSLEDOVATEL;Russian Atomic Energy Authority). The dose rate was 6 kGy/h. Theuncertainty in the gamma dose was found to be less than 1%. Theactivity of the cell was 5.97 � 1014 Bq. The films were positionedat the center of the driving belt and the irradiation process was car-ried out automatically. The detector films were irradiated at differ-ent gamma doses ranging from 5 � 105 to 1 � 106 Gy. The filmswere irradiated for various times in order to deliver the variousdoses. These irradiations were performed at the Gamma Division,Atomic Energy Authority, Cairo. The nature of the thermal stabilitychanges induced in the PADC films by the c-irradiation at differentdoses was analyzed by means of TGA. TGA was carried out under anitrogen stream at a flow rate of 20 mL min–1 on a Shimadzu 50 Hthermal analyzer fabricated in Japan. The temperature rangecovered was 30–600 �C. Thermal analyses of the detector filmsexposed to high gamma doses were performed at the MicroanalysisCentre of Cairo University.

Fig. 1. TGA thermograms of a pristine PADC film and films irradiated with c-rays at differ

4. Results and discussion

Thermal degradation is a crucial process, providing vital infor-mation on polymer structure from the point of view of thermal sta-bility, the temperature range in which the polymer can be applied,and the activation energy associated with the overall degradationprocess. PADC polymer-based NTDs exposed to different doses ofc-rays were heated from about 30 �C to around 600 �C and theprogressive weight losses were recorded. Fig. 1 compares the ther-mograms of pristine and c-ray-irradiated PADC films, showing theweight loss (%) as a function of temperature. The temperatures Tend

(�C) corresponding to the onset of decomposition and the threedecomposition zones, major, minor, and residual, are summarizedin Table 1. The temperature at which the mass change reaches amagnitude that the thermo-balance can detect was taken as theonset of decomposition temperature, and was found to be about158 �C for the pristine PADC sample. It was observed to besomewhat raised in the irradiated samples, measured as about163, 172, 168, 172, and 177 �C for the PADC films exposed to500, 600, 700, 800, and 900 kGy of c-rays, respectively. However,the sample exposed to 1000 kGy dramatically showed the oppositeeffect, its onset of decomposition temperature being just 89 �C.Fig. 1 also shows that in the case of no gamma dose the polymer

ent doses up to 1000 kGy (a) stacked thermograms and (b) composed thermograms.

Table 1Temperatures corresponding to the percentage weight losses at the end of the stable zone and the thermal decomposition zones, Tend (�C), of PADC-based CR-39 NTDs exposed todifferent doses of c-rays.

Gamma dose (kGy) Tend (�C)/percentage weight loss

Stable zone 1st unstable zone: major decomposition 2nd unstable zone: minor decomposition 3rd unstable zone: residual decomposition

0 158/�0 400/69.83 484/24.50 600/5.35500 163/�0 391/67.05 488/32.57 600/0.48600 172/�0 386/68.05 493/30.65 600/0.70700 168/�0 386/71.80 484/27.66 600/0.52800 172/�0 372/65.96 479/31.37 600/2.63900 177/�0 381/69.99 479/24.89 600/5.13

1000 88/�0 377/67.98 479/27.31 600/4.20

A.F. Saad et al. / Nuclear Instruments and Methods in Physics Research B 325 (2014) 79–83 81

film underwent a weight loss of 69.83% at around 400 �C followedby a further 24.5% at around 484 �C, and that 5.35% weightremained at the end of the temperature range. The films exposedto c-ray doses of 500, 600, 700, 800, 900, and 1000 kGy underwentweight losses of 67.05%, 68.05%, 71.80%, 65.96%, 69.99%, and67.98% at around 391, 386, 386, 372, 381, and 377 �C, respectively,and residues of 0.48%, 0.70%, 0.52%, 2.63%, 5.13%, and 4.20%remained at the end of the temperature range, as indicated inTable 1. It should be mentioned that there was an irregulardecrease in thermal stability of the irradiated PADC samples.

Fig. 2 shows the first-derivative decomposition curves obtainedfor the pristine and c-ray-irradiated PADC films. For the pristinefilm, the first and second Tmax peaks were located at 370 and441 �C, respectively. For the irradiated PADC samples, however, anew derivative peak induced by the c-rays was observed, in addi-tion to the aforementioned two typical decomposition peaks. Theresults are summarized in Table 2. It should be noted that for thedecomposition zone induced by c-rays, Tmax was found to varyonly from 297 to 288 �C for doses ranging from 500 to 900 kGy,

Fig. 2. Weight-loss derivative curves of a pristine PADC film and films irradiated with cthermograms.

whereas at 1000 kGy a higher value of 314 �C was measured. How-ever, the Tmax values of the characteristic decomposition zones,major and minor, were found to remain at around 370 and441 �C, respectively, in the pristine and irradiated films, asreported in Table 2. For more quantitative analysis, the area underthe first-derivative curve gives a measure of the total mass loss forthe process. This was found to increase with increasing gammadose up to a maximum at 700 kGy, but then sharply decreased at800 kGy, remaining constant thereafter as shown in Fig. 3a. Thearea under the second-derivative curve and the new derivativepeak induced by c-rays showed more or less the same behaviour,as can be seen in Fig. 3b and c, respectively. It should be noted that,over the whole gamma dose range, there were increases of 75% and90% in the total mass losses for the first- and second-derivativecurve peaks, respectively. For the peak induced by c-rays, from 0to 700 kGy there was a very sharp increase from 0% to 160% inthe total mass loss, and then from 700 to 1000 kGy there was avery sharp decrease in the mass loss, as shown in Fig. 3 c. It is veryinteresting to note that the thermal stability of a PADC film

-rays at different doses up to 1000 kGy (a) stacked thermograms and (b) composed

Table 2Temperatures of maximum mass loss rate Tmax (�C) in the thermal decomposition of PADC-based CR-39 NTDs irradiated with different doses of c-rays.

Gamma dose (kGy) Tmax (�C)

c-ray-induced zone Characteristic major zone Characteristic minor zone

0 ND 370 441500 297 374 445600 305 371 440700 297 369 443800 293 370 444900 288 366 442

1000 314 365 437

ND: Not detected.

0

0.02

0.04

0.06

0.08

0.1

0.12

0 200 400 600 800 1000 1200

Gamma dose (kGy)

(der

ivt-

Wei

ght l

oss)

(A

rbitr

ary

units

)

0

0.02

0.04

0.06

0.08

0.1

0.12

0 200 400 600 800 1000 1200

Gamma dose (KGy)

deri

tv-W

eigh

t los

s

(Arb

itrar

y U

nits

)

Gamma dose (KGy)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 200 400 600 800 1000 1200

deri

tv-W

eigh

t los

s

(Arb

itrar

y U

nits

)

A B

C

Fig. 3. Weight-loss derivative results of PADC film as a function of gamma dose. The area under the derivative curve gives a measure of the total mass loss for the process(a) the first-derivative curve, (b) the second-derivative curve and (c) the new derivative peak induced by c-rays, respectively.

82 A.F. Saad et al. / Nuclear Instruments and Methods in Physics Research B 325 (2014) 79–83

exposed to a dose of 700 kGy of c-rays was significantly altered.The PADC film must have undergone a significant degree ofscission of its long-chain molecules, converting them into shorterfragments, as a result of the c-ray exposure. Indeed, the PADC filmbecame permanently softened, resulting in an increase in the totalmass loss and a decrease in the thermal stability and thermobalance thresholds at certain c-ray doses.

The activation energy Ea is defined as the minimum energyrequired to start a chemical reaction. In the present case, it refersto the energy needed to activate the molecules constituting the

physical system to undergo a phase transition. Activation energyis best regarded as an experimentally determined parameter thatindicates the sensitivity of a reaction rate to temperature. Hence,it must be measured to assess the thermal stability of a heat-resist-ing polymer material.

Fig. 4 shows plots of ln h=h0 versus 1/T (1000/k) for the pristinefilm and films exposed to different doses of c-rays. Using a least-squares fitting method, the activation energies of thermaldecomposition in the PADC films were deduced from the slopesof the straight lines in Fig. 4. The activation energies of the PADC

1st derivative

2nd derivative

y = -8.2136x + 11.813

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0 1.4 1.5 1.6 1.7 1.8 1.9 2

ln(h

/ho)

1000/T (k-1)

y = -2.4888x + 3.0942

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0 1.3 1.35 1.4 1.45

ln(h

/ho)

1000/T (k-1)

Fig. 4. Plot of the logarithm of normalized weight loss as a function of inversetemperature 1/T.

Table 3Activation energies Ea (eV) for the thermal decomposition of PADC-based CR-39 NTDsirradiated with different doses of c-rays.

Gamma dose (kGy) Activation energy (eV)

1st order 2nd order

0 0.71 0.20500 0.54 0.19600 0.58 0.18700 0.47 0.16800 0.51 0.17900 0.52 0.17

1000 0.41 0.21

A.F. Saad et al. / Nuclear Instruments and Methods in Physics Research B 325 (2014) 79–83 83

films irradiated with different doses of c-rays are collected inTable 3. The activation energy of the first-step decompositiondecreases with increasing gamma dose, making the PADC polymermore susceptible to thermal decomposition. For the second-stepdecomposition, however, irradiation was observed to have moreor less the same effect, except at a dose of 1000 kGy, whereuponthe activation energy was enhanced.

5. Conclusion

The TGA thermograms indicated a degradation of the polymerbackbone under gamma irradiation, making the material moresusceptible to decomposition than a pristine film. Analysis ofweight-loss derivative data showed a clearly discernible effect onthe thermal stability, which was most prominent at a dose of700 kGy. An increase in the weight-loss derivative of the PADC filmby this dose further enhances the potential usable range of thispolymer in high-temperature applications. The first- and second-step activation energies of thermal decomposition of a PADC filmare differently affected by c-irradiation. The c-irradiation predom-inantly induced chain-scission in the polymer material. Theactivation energies were lowered by around 24% and 42% for thefirst-step process and by around 5% for the second-step processin the samples irradiated with the lowest and highest doses, 500and 1000 kGy, respectively. The PADC film-based nuclear trackdetector (in the form of CR-39) may be of use for industrialapplications as a result of its high response to c-rays.

Acknowledgements

We gratefully acknowledge the gamma irradiation team atRadiation Technology Center, Atomic Energy Authority, Cairo, forthe help during the irradiations.

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