Etching Properties of Polyethyleneterephthalate (PET) Melinex-E Nuclear Track Detectors (NTDs)

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1 Etching Properties of Polyethyleneterephthalate (PET) Melinex-E Nuclear Track Detectors (NTDs) E. H.Ghanim* a, A. Hussein b, H. M. El-samman b, and S. P. Tretyakova c a Department of Basic Sciences, Faculty of Industerial Education, Beni-Sueif University, Beni- Sueif, East of Nile, Egypt. b Physics Department, Faculty of Science, Menoufia University, Shebin El-koam, Egypt. c Joint Institute for Nuclear Research(JINR), Dubna, Russia. * - emadhamed_65@yahoo.com (E. H. Ghanim) ABSTRACT One of the main parameters that control track formation is the bulk etch rate, V B. The dependence of V B on etchant concentrations and temperatures was extensively carried out. It is found that, V B of the PET Melinex-E (C 10 H 8 O 4 ) depends upon the etchant temperature T through an Arrhenius equation. While, the dependence of V B on the etchant concentration; C followed the relation V B = A C n. The activation energy of etching, E b, for the studied Melinex-E detector was calculated. An average value of E b = 0.83 ± 0.03 ev was extracted. The variation of, V B, of PET with etching duration was studied and compared with that of CR-39 plastic at certain etching temperature; T e =60 o C and at different etchant concentrations. The irradiation facilities were performed with the 252 Cf fission fragments and 129 Xe +8 (θi =π/2). Results of these studies were discussed in the frame work of nuclear track formation and etching theories. Key words:pet, CR-39 detectors, chemical etching, V B determination, 129 Xe and 252 CF ions INTRODUCTION A great deal of interest has been focused on the use of solid state nuclear track detectors (SSNTDs) in a large variety of applications in science and technology [1-3]. These applications include up-to-date studies in nuclear, cluster and fission physics, charged particle radiography, micro filters, industrial and medical applications [4-6]. Improvement in the understanding of track formation mechanism and related processes will further widen the application spectrum of these detectors [7-10]. Operation of the solid state nuclear track detector is based on the fact that a heavy charged particle will cause extensive ionization in the material when it passes through [11-12]. The main parameters that govern track formation are the bulk etch rate V B and track etch rate V T. Dependence of V B on different parameters such as the preparation procedures, etching conditions, irradiation before etching, environmental conditions etc. must be taken into account [13-15]. To count etched tracks easily, the shape and size of etched track must be applied to distinguish true tracks from other features such as scratches, surface contamination or defects within the plastics [16-17]. 323

2 Among these SSNTDs, PET plastic, a polymer of Polyethyleneterephthalate Melinex E (C 10 H 8 O 4) or (C 5 H 4 O 2 ) n is the most commonly used as nuclear track microfilters and nuclear membranes [18-20]. Because of its low radiation sensitivity, PET can be used as SSNTD for the detection of fission fragments and other heavily ionizing particles in a high background of lighter particles (p, d, α) [21]. In spite of the scientific and technical applications of PET for particle track etching only a few attempts have been made to elucidate the kinetics of particle track etching in this material [22]. This paper includes a study of chemical etching properties of Polyethylene terephthalate (PET) Melinex-E nuclear track detectors. The etchant concentration was varied from 2.5 up to 10.0 N NaOH, under different etching temperature T e (40-90 o C). The bulk etch rate V B was measured by standard method (Mass decrement method), fission fragment and heavy ion track diameter method. (1) Materials EXPERIMENTAL PROCEDURES (i) PET Melinex - E A PET Melinex E detector sheets of molecular formula (C 10 H 8 O 4 ), thickness 185 µm and density ρ = 1.39 gm/cm 3 (TRADE MARK: by Imperial Chemical Industries, Ltd., England) were used. The PET sheets were cut into pieces of about 3 cm x 3 cm to minimize errors in calculation of V B with mass decrement method. (ii) CR-39 An allyl digylicol carbonate CR-39 (C 12 H 18 O 7 ) TASTRAK films (Track Analysis System Limited, Bristol, U. K.) of about 300 µm thickness were used for comparative study. (2) Bulk etch rate; V B Measurements For bulk etch rate determination of Melinex E we apply the following relation:- V B = m / 2Aρt e (1) Where m is the weight decrement of the PET detectors before and after etching process, A is surface area of the used film, ρ is the density of the detector and t e is the etching time. In case of heavy ion tracks, V B was calculated using the following relation V b = D X / 2t e (2) Where D X is the track diameter of the heavy ion energetic projectile. (3) Irradiation Facility (i) PET irradiation PET samples were irradiated at room temperature by 129 Xe +8 (E = 1.0 MeV/n, F = ions/cm 2 ), at Joint Institute of Nuclear Reaction (JINR ) Flerove Laboratory of Nuclear Reaction ( FLNR ), Dubna, Russia. The plastic samples have been irradiated normally relative to the detector surface using 129 Xe +8 and fission fragment of 252 Cf source (1.0 µci). 324

3 (ii) CR-39 irradiation The plastic sheets used in this study were exposed in air to fission fragments (f.f), from 252 Cf source through 2π geometry. (4) Equipments setup (i) Etching of exposed detectors For etching process a Julabo water bath and Kottermann shaker, of stabilizing temperature accuracy ± 0.5 and ± 1.0 ο C respectively, were used. All etched samples were held at the same depth of etchant. After etching, PET detectors were washed in running water for suitable time interval and then washed in distilled water for sufficient time using an ultrasonic cleaner bath to remove etchant and etch products from the surface of the detector. Finally, the films were carefully dried before they were weighted again for mass decrement measurements. (ii) Track parameter measurements The diameter of circular fission fragment tracks in CR-39 detectors as well as 129 Xe +8 and f. f tracks in Melinex-E PET were measured after each etching step under suitable etching conditions. The diameters of tracks in all the exposed detectors were measured using an optical microscope, (BH-2), with a magnification of 600 X and uncertainty of about ± 0.22 µm. The diameters of 200 tracks (100 from each of two kind detectors) in the case of fission fragments particles as well as 129 Xe +8 tracks were counted. RESULTS AND DISCUSSION Bulk etch rate V B of Melinex-E detectors was determined in a temperature range from 40 up 90 ο C in step of 5 ο C with different concentrations of NaOH, viz. 2.5, 4, 5, 6.25, 7, 8 and 9 N. The bulk etch rate data represented against etching temperature T e in the concentration range N of NaOH etchant are given in fig. 1 (as an example), where V B is plotted versus T e and results are represented by the following equation: V B = A exp. (-E b /kt) (3) PET 185 NaOH Exponential Fit, VB = A exp.(bt) C=2.5 N Bulk etch rate VB ( m /hr) 8.00 C =4 N C = 5 N C=6.25N Etching Temperature Te (C ) Fig. (1) Variation of V B B with etching temp., T e, using 185 μ m PET foils. 325

4 It is clear from fig. 2 that the dependence of Ln V B on 1000/T (K ) reflects an exponential behaviour of VB with T e. The results of V B with T e can be denoted by the relation: 3 Ln V B = Ln A (E b /10 k) 1000/T (4) where A is a constant, Eb is the activation energy of bulk etching and k is the Boltzmann's constant. Using a least square fit method; the values of E b were calculated from the slopes of the straight lines given in figure 2. An average value of E b was found to be 0.83 ev, where the maximum deviation in E b was less than 3 %. -1 PET 185 NaOH Fit Eq. LnVB= LnA - Eb/kT LnVB =Lna+nLnC - Eb/kT C=2.5N Bulk etch rate Ln VB ( m / hr ) 2.00 C=4N C=5N C=6.25N C=7N C=8N C=9N Resiprocal of etching temperature 1000/T ( k ^ -1 ) Fig.(2) Relation between Ln VB and 1/T at varying etchant concentration of 185 μm PET foils. It was found that the constant of proportionality, A, in equation (3) is a function of etchant concentration C as shown in fig. 3. The best fit of data is a power law with high regression factor of about 96 % PET 185 Power fitting, A = f (c) A = a C^n, Regresion Parameter of the fitted function a = n = 1.86 R= A = f (c) x10^-4 ( m / hr) Etching Concentration C ( N ) Fig. (3) The dependence of the constant A (see eqn. 3) on C. 326

5 The dependence of V B on etchant concentration was also studied. Figure 4 shows the variation of V B with C at temperatures of 40, 45, 55, and 60 0 C. Data of Fig. (4) can be fitted through an empirical power representation in the form n V B B = A1 C 1 (5) PET 185 NaOH Fit Eq. Power: VB = ac^n Bulk etch rate VB ( m / hr) Te=40 C Te=45 C Te=55 C Te=60 C 0.40 Fig. (4) Variation of V BB with Etchant concentration C (N) etchant Concentration, C, at different etching Temp., T e, of a 185 μm PET Plastics. Values of A 1 and were n 1 then calculated from the slopes of the straight lines given in Fig. (5) and Fig. (6) as follows. PET 185 NaOH Fit Eq.: Linear Ln VB =Ln a + n Ln C Te=40 C R.P.= Te=45 C TE=55 C R.P.=0.98 R.P.=0.97 Bulk etch rate Ln VB ( m / hr ) Te=60 C Te=65 C R.P=0.97 R.P.= Etchant concentration LnC (N) Fig. (5) Variation of Ln V B B with Ln C, at different etching Temp., T e, of a 185 μm PET foils. 327

6 6.00 PET 185 NaOH Fit Eq.: Linear Ln VB =Ln a + n Ln C Te=70 C R.P.=0.93 Te=75 C Te=80 C R.P/=0.92 R.P.=0.91 Bulk etch rate Ln VB ( m /hr ) 2.00 Te=85 C Te=90 C R.P.=0.94 R.P.= Fig. (6) Variation of Ln V BB with Etchant concentration LnC (N) Ln C, at different etching Temp., T e, of a 185 μm PET foils. Table 1 contains the extracted values of A 1 and n 1 with the etching temperature. The average values of A 1 and n 1 were, respectively, found to be and 1.53x Table 1. Displays the values A 1, and n 1 given in equation (5). T e (C) n A x x x x x x x x x x x10 11 Accordingly a general formula of V B extracted from equation (5) can be take the form: V B = x10 11 C exp (E b /kt) (6) In Fig. (7) Values of V B B calculated from equation (6) are correlated with the experimental data with good verification. 328

7 B IX Radiation Physics & Protection Conference, November 2008, Nasr City - Cairo, Egypt V B = 1.53x C exp(-e b /kt) V B (μm/hr) T=40 C T=45 C T=50 C T=55 C T=60 C T=65 C T=70 C T=75 C T=80 C T=85 C T=90 C Calc.40 Calc.45 Calc.50 Calc.55 Calc.65 Calc.70 Calc.75 Calc.80 Calc.85 Calc.90 Calc C (N) Fig. (7) Representation of calculated (using eqn. 6) V BB values experimental values (given in data). ( given in solid curves) and the The behaviour of V B of PET with etching duration t e was studied at T e = 60 o C using etchant concentration ranged from 2.5 N to 9.0 N of NaOH. Fig.8 studies the variation of V B with etching time t e from 2.0 up to 44.0 hrs. In the first few hrs. V B shows a decrease and then remains almost constant. The beginning decrease in V B might be due to the decrease in oxygen [23] as one goes deeply through the detector. PET -185 m Na OH Te = 60 C C1= 2.5 N C2= 4 N Bulk etching rate VB ( m / hr ) C3 = 5 N C4 = 6.25 C5 = 7 N C6 = 8 N C7 = 9 N etching time te (hr) Fig.(8) The behaviour of V B, with duration of etching at fixed etchant concentration o using 185 μm PET Melinex-E etched at constant etching Temperature, Te= 60 ( C). Fig. 9 represents the dependence of VB on t e both PET and CR-39 foils etched in 5 N o NaOH at T e =60 C for a matter of comparison. It is clear from Fig 9 that the stability in VB is much more obvious in case of CR-39 than that in case of PET foils. 329

8 1.20 5N NaoH, Te = 60 C 1.10 PET CR Bulk Etch rate VB ( m/ hr) Fig. (9) The behaviour of V B, B with T o NaOH at T e = 60 ( C) etching time te (hr ) e using of 185 μm PET and 300 μm CR-39 etched in 5N The values of VB were also determined using the fission track method. Fig.10 illustrates the relation between fission track diameter, D ff, with t e using PET foils etched in 6.25N NaOH at 60, 70, and 75 o C. Comparing results of V B in Fig.10 with those obtained from mass decrement method, one can finds reasonable agreements with deviations better than 5%. 4 PET m 6.25N NaOH Te = 60 C Te = 70 C Track Diameter Dff ( m) Te = 75 C VB= , R. P.= 99.7 % VB= , R. P.=98.9 % VB= , R. P. =95 % etching time te (hr) Fig. (10) Relation between fission track diameter, D ff, and etching time, t e, of 185 μm PET foils etched in 6.25N NaOH at different etchant temperatures, T e. Fig.11 shows the relation between D ff in CR-39 with t e at etching condition of 6.25 N NaOH at 60 and 70 o C where one can easily extract the V B values from the slopes of these straight lines and using eqn. (2). 330

9 CR-39 T = 60 C T = 70 C Track diameter Dff ( m ) VB= , R.P= 97 % VB= R. P =95 % Etching time te ( hr ) Fig. (11) Relation between D ff, and t e of 300 μm CR-39 foils etched in 6.25N NaOH at different etchant temperature T e. Also, fig. 12 shows the variation of track diameter with t e using 129 Xe +8 and ff ions in PET etched in 5 N and 6.25N NaOH, respectively at 60 o C. Data extracted from both figures (see 11 and 12) are in good agreement with those resulted from the mass decrement method. 2 PET m Te= 60 C, NaOH Xe (129 Mev), C= 5 N f.f, C = 6.25 Track diameter Dx ( m) VB= , R. P. = 97.8 % VB = , R. P. =97.5 % Etching time, te (hr) Fig. (12) Variation of Track diameter D x ; of two heavy ions 129 Xe & ff 252 Cf with etching time; t e in 185 μm PET Plastics etched in 5N and 6.25 N NaO respectively, at T e =60 o C CONCLUSION The detailed studies on V B determination reflects the strong dependence of V B on C and T. Also, these values of V B can usefully be used in future without any further measurements. Also, the above results can be used to determine the response function of Melinex-E and to identify between heavy ions with different E, Z, A on the basis of measured track diameter as well track length and related parameters. 331

10 Throughout the present work the V B determination of plastic foils was obtained using different methods. Detailed studies were carried out in case of mass decrement method where different values of etchant concentrations and temperatures were included using PET foils. An important semiempirical formula is deduced in order to relate V B with both C and T of NaOH etchant solution, where V B is given by V B = x10 11 C exp (E b /kt), E b = 0.83 ± ev. The importance of this relationship is to provide a user with fast, quick estimation of V B values if he /she knows both C and T. Moreover, the determination of V B using the track diameter measurements of either fission or Xe ions provides additional results to assure the validity of using such V B relationship given above. REFERENCES (1) P. B. Price, Radiat. Meas., 43 (2008) S19-S25. (2) Reimar Spohr, Radiat. Meas., 40 (2005) (3) V. V. Shrikova, S. P. Tretyakova, Radiat. Meas., 34(2001) (4) S. P. Tretyakova, Radiat. Meas., 25(1995) (5) P. Apel, Nucl. Inst. and Meth. B 208 (2003) (6) V.R.Oganessian, V.V.Trofimov,J.Vetter,B.Dorschel, D.Hermsdrof, Radiat. Meas., 37 (2003) (7) Mukhtar Ahmed Ranna, Nucl. Inst. Mth. B 266 (2008) (8) M.Abdesselam M.Djebara, A. C. Chami, M. Siad, Nucl. Inst. and Meth. B 266 (2008) (9) B. Basu, S. Biswas, S. Dey, A. Maulik, A.Mazumdar, S.Raha, S.Saha, Swapan K.Saha, D.Syam, Rad. Meas. 43 (2008) S262-S265. (10) B.Basu, S.Dey, B.Fischer, A.Maulik, A.Mazumdar, S.Raha, S.Saha, D.Syam, Rad. Meas. 43 (2008) S95-S97. (11) A. Hussein, S.A.Hager, M.K. El-Nimr ande.h.ghanim, Nucl. Instr. Meth. B 88 (1994) (12) A. Hussein, S.A.Hager, A.M.I. Kany, M.K. El-Nimr ande.h.ghanim, Radiation Effects Defects in Solids 139 (1996) (13) A.A.Abbou El-kheir, A.Hussein and Kh.Shnishin, Radiat.Phys.Chem.47, 4(1996)527. (14) A. Hussein,Kh.Shnishin and A.A.Abou El-kheir, J.Mater.Sci 28 (1993) (15) D.Hermsdrof, M.Hunger, S. Starke, F.Weickert, Radiat. Meas. 42(2007)1-7. (16) V. Ditlov, Radiat. Meas. 40(2005) (17) D. Nikezic, K. N. Yu, Materials Science and engineering R 46 (2004) (18) A.I.Vilensky, D.L.Zagorski, S.A.Bystrov, S.S. Michailova, R.V.Gainutdinov, A.N. Nechaev, Surface Science (2002) (19) Z.Y.Zhu,J.L.Duna,Y.Mackawa,H.Koshikawa,M.Yshida,Radiat.Meas.38(2004)255. (20) S.P.Tretyakova, Sov. J. Part. Nucl. 23 (2) (1992) (21) H.B.Luck, Nucl. Inst. Meth 213 (1983)507. (22) S.P.Tretyakova, P. Apel, L.Joles, T.Mamonova and V.Shirkova, Solid state Nuclear Track Detectors, pergamon press, Oxiford and Newyork, (1980)283. (23) T. Yamauchi, Radiat. Meas. 36 (2003)