- Email: [email protected]
Some more new etchants for CR-39 detector
Radiation Measurements 39 (2005) 551 – 555 www.elsevier.com/locate/radmeas
Short communication
Some more new etchants for CR-39 detector Matiullaha,∗ , S. Rehmana,1 , S. Rehmana,2 , N. Matib , S. Ahmadb a Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O.Nilore, Islamabad, Pakistan b Department of Physics, Government College Satellite Town, Rawalpindi, Pakistan
Received 30 August 2004; accepted 7 October 2004
Abstract Recently, several new etchants have been reported for CR-39 detector (Molten Ba(OH)2 . 8H2 O as an etchant for CR-39 detector, Radiat. Meas. 37 (2003) 205; Discovery of new etchants for CR-39 detector, Radiat. Meas. (2004)). We have made further progress in this direction and have unveiled two more new etchants which are reported in this article. CR-39 detectors were irradiated with fission fragments and alpha particles from a thin 252 Cf disc source. The irradiated detectors were then etched in our newly introduced etching solutions as well as in conventionally used 6 M NaOH aqueous solution at 70 ◦ C. The newly prepared etching solutions included NaOH dissolved in methanol and NaOH dissolved in methanol + water. Optimum values of NaOH concentration in methanol as well as in methanol + water were determined. Optimum etching temperatures were also determined for both the above-mentioned etchants. From fission and alpha track diameters, bulk etching rate (VB ), track etching rate (VT ) and etching efficiency () were determined and compared with that obtained for 6 M NaOH at 70 ◦ C. Both the newly introduced etchants were found more efficient than the conventionally used 6 M aqueous NaOH (64%) at 70 ◦ C and have relatively much smaller etching time. © 2004 Elsevier Ltd. All rights reserved. Keywords: Chemical etching; Processing time; NaOH/methanol; SMW solution; Etching efficiency
1. Introduction CR-39 is the most popular member of the SSNTD’s family (Cartwright et al., 1978). It has been widely used in many fields of science and technology (see, for example, Durrani and Bull, 1987; Fleischer et al., 1975; Matiullah et al., 1988a,b,1990,1991,2001; Khan et al., 1991; Rashid et al., 1993; Benton and Richmond, 1986; Brandt, 1993; Qureshi et al., 1991; Bashir et al., 1993; Matiullah, 2000; Dwivedi, 1997). Besides working on improving the quality ∗ Corresponding author. Tel.: +92 051 220 7380;
fax: +92 051 922 3727. E-mail address: [email protected] (Matiullah). 1 Shafi-ur-rehman. 2 Shakeel-ur-rehman. 1350-4487/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2004.10.009
of CR-39 detector, continuing efforts have been made to discover new etchants for which CR-39 detector have higher efficiency and shorter etching time. This is desirable because the chemical etching techniques reported for CR-39 detectors are time-consuming. Aqueous solutions of the hydroxides of alkali metals (group-IA) viz. NaOH and KOH have been extensively studied as etchants for CR-39 detector (see, for example Durrani and Bull, 1987). Tahiri et al. (2003) studied groupIIA metal-hydroxides such as Mg(OH)2 , Ca(OH)2 and Ba(OH)2 · 8H2 O, dissolved in distilled water. They have reported that molten Ba(OH)2 · 8H2 O is more efficient than that of 6 M NaOH aqueous solution. In addition to this, etching time is drastically reduced if molten Ba(OH)2 · 8H2 O is used as an etchant. Matiullah et al. (2005) went one step further and reported two more new etchants, namely
552
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555
NaOH/ethanol and NaOH/1-propanol. They found that 1 M NaOH/1-propanol solution at 49 ◦ C yields a maximum value of etching efficiency (∼70%). Whilst 1.5 M NaOH/ethanol yields maximum value of etching efficiency (∼77%) at 55 ◦ C. Both of the above-mentioned etchants are more efficient than the aqueous 6 M NaOH solution at 70 ◦ C. Like molten Ba(OH)2 · 8H2 O etching time is also drastically reduced when NaOH/ethanol and NaOH/1-propanol are used as etchants. We have now made further progress and have unveiled two more new etchants which are dealt with in this article. These include NaOH dissolved in methanol and NaOH dissolved in methanol + water (from now onward called SMW solution).
2. Experimental procedures CR-39 sheets of thickness 500 m, and supplied by Page Mouldings, Ltd., UK, were cut into small detectors of size 3 cm × 2.5 cm each. These detectors were irradiated with normally incident alpha particles and fission fragments from a thin source of 252 Cf. These detectors were then etched in NaOH/methanol and SMW solution at different concentrations and etching temperatures. After each etching step, detectors were washed under running water and then with distilled water. Diameters of the fission fragment and alpha particle tracks were measured under an optical microscope. Optimum values of etching temperature and concentration were determined. VB , VT and etching efficiency () were calculated using track diameter method (Henke et al., 1986; Matiullah et al., 2001). The values obtained for new etchants were compared with those obtained for CR-39 detectors etched in conventional 6 M aqueous solution of NaOH at 70 ◦ C.
3. Results and discussion Various concentrations of NaOH/methanol and SMW solutions were prepared. CR-39 detectors irradiated with fission fragments and alpha particles were etched in conventional 6 M aqueous solution of NaOH at 70 ◦ C and in the above-mentioned prepared NaOH/methanol as well as SMW solutions at different temperatures in order to achieve the optimum processing conditions for the newly introduced
etchants. From measured track diameters data, VB , VT and were determined using the following equations (Durrani and Bull, 1987): VB = Dff /2t,
(1)
VT = VB (1 + x 2 )/(1 − x 2 ),
(2)
= 1 − (VB /VT ),
(3)
V = VT /VB ,
(4)
where Dff represents average fission track diameter; D is the average alpha diameter; t is the etching time; is the track etching efficiency; V is the sensitivity and x =D /Dff . Table 1 shows the observed average track diameters, VB , VT and values for CR-39 detectors that were etched in the listed concentration of conventionally used NaOH solution at 70 ◦ C. As expected, both Dff and D are seen to increase with etchant concentration. About 6 M concentration yields the highest value of the efficiency (64%) which is in agreement with the experimental error with the published data (Durrani and Bull, 1987). 3.1. NaOH/methanol etchant Having verified already published etching parameters data for 6M NaOH at 70 ◦ C, we now present our data concerning determination of the optimum values of etchant concentration and temperature for NaOH dissolved in methanol. First, the effect of temperature was studied. To do so, CR39 detectors, irradiated with fission fragments and alpha particles, were etched in 1.5 M NaOH/methanol solution at different temperatures. There was not any special reason behind choosing the value 1.5 M of NaOH/methanol solution. In fact any other value would have also yielded similar results. Figs. 1 and 2 show average track diameters of fission fragments and alpha particles as a function of etching time for 1.5 M NaOH/methanol solution at the listed temperatures. As was expected, track diameter is seen to increase with an increase in the temperature of the etching solution. Initially, at lower values of the temperature (i.e. from 40 to 45 ◦ C), increase in the track diameter is negligibly small. Beyond 12 min etching time, increase in the track diameter becomes significant. It is clear from the above figures that at any etching time, higher values of the etching temperatures yield
Table 1 D , Dff , VB , VT and values of CR-39 detectors for the listed concentration of NaOH solution at 70 ◦ C Etchant conc. (M)
D (m)
Dff (m)
VB (m h−1 )
VT (m h−1 )
(%)
4 6 8 10 12
8 9.67 10.66 15 23
15 19.66 24 29.33 47.66
1 1.25 1.75 2.26 3.38
2.34 5 6.96 6.23 7.61
35.6 64 56.8 41.3 37.4
Fission fragment track diameter (µm)
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555
Table 2 VB , VT and etching efficiency of CR-39 detector for 1.5 M NaOH/methanol solution at the listed temperatures
55˚C 35 30 25
45˚C
20
553
50˚C 40˚C
15 10
Etchant temperature VB (◦ C) (m h−1 )
VT (m h−1 )
Sensitivity (v)
(%)
40 45 50 55 60
107.169 99.907 41.15 284.72 122.81
3.5714 2.831 4.33 4.55 3.78
72.00 64.68 76.91 78.04 73.5
30.007 35.28 9.5 62.5 32.43
5 2
4
6
8 10 12 14 Etching time (min)
16
18
20
22
80 78
Fig. 1. Average fission fragment track diameter as a function of etching time. Here CR-39 detectors were etched in 1.5 M NaOH dissolved in methanol at the listed temperatures.
76 Efficiency (%η)
74
30
Alpha track diameter (µm)
55°C
72 70 68 66 64
20
62
45°C 50°C
60 40°C
10
40
45 50 55 Etching Temperature (°C)
60
Fig. 3. Efficiency of CR-39 detector as a function of temperature for 1.5 M NaOH dissolved in methanol.
0 4
8
12 16 Etching time (min)
20
24
Fig. 2. Average alpha-particle track diameter as a function of etching time in CR-39 detectors etched in 1.5 M NaOH dissolved in methanol at the listed temperatures.
greater values of track diameters and hence higher VB and VT values. At 55 ◦ C, the track diameter increases steeply with an increase in the etching time. From these figures it may be clearly seen that only several minutes are required to have reasonable size of track diameters. This is a great advantage over 6 M NaOH aqueous solution where several hours of etching would have been required to get similar track diameters. From the measured track diameter data, VB , VT and were calculated. The results obtained are shown in Table 2. For clarity, the data shown in this table is plotted in Fig. 3. It can be seen in Fig. 3 that NaOH/methanol yields maximum value of (∼78%) at 55 ◦ C.
Having determined optimum etching temperature, we then studied the effect of concentration on the of CR-39 detector. Fig. 4 shows etching efficiency as a function of the etchant concentration. It is obvious from this figure that 1.5 M NaOH/methanol solution at 55 ◦ C yields maximum value of the efficiency. 3.2. NaOH/(methanol+water) etchant Our next newly discovered etchant is SMW solution. SMW is the solution that contains 10% NaOH dissolved in X% methanol and (90–X)% water. Since NaOH/methanol solution has maximum efficiency at 55 ◦ C (see Fig. 3), we used the same value of the temperature for SMW etchant. We then studied the effect of varying percentage of methanol in SMW solution on track diameters of alpha particles and fission fragments. Results obtained are plotted in Figs. 5 and 6 for the listed percentage values of methanol in SMW solution. Track diameter is seen to increase linearly with an increase in X value.
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555
80
60
75
50 Fission track diameter (µm)
Etching efficiency (%η )
554
70
65
60
55 1
1.25
1.5
1.75
X = 40 X = 50 X = 60 X = 70 X = 80
40
30
20
10
1.78
Etchant Conc.(mol l-1)
0
Fig. 4. Etching efficiency of CR-39 detector as a function of NaOH/methanol concentration at 55 ◦ C.
8
12 16 Etching time (min)
20
Fig. 6. Average track diameter of fission fragments as a function of methanol concentration (X%) in SMW solution at 55 ◦ C.
40
Table 3 VB , VT and etching efficiency of CR-39 detector for the listed concentrations of methanol (X%) in SMW Solution at 55 ◦ C
X = 40 X = 50 X = 60 X = 70 X = 80
30 Alpha track diameter (µm)
4
20
Methanol (X%)
VB (m m−1 )
VT (m m−1 )
Sensitivity (v)
(%)
40 50 60 70 80
0.1875 0.594 0.71 1.292 1.166
0.487 1.639 3.7 6.092 3.596
2.6 2.76 5.212 4.715 3.082
61.5 63.76 80.81 78.79 67.54
10
maximum efficiency (∼81%) is achieved at 60% methanol concentration in SMW solution, i.e. optimum percentage ratio of methanol/water lies around 60/30 with 10% NaOH. 0 4
8
12 16 Etching time (min)
20
Fig. 5. Average track diameter of alpha particles as a function of methanol concentration (X%) in SMW solution at 55 ◦ C.
From measured track diameter data, shown in Figs. 5 and 6, VB , VT and were calculated which are shown in Table 3. For greater clarity, etching efficiency () shown in Table 3 is plotted as a function of methanol concentration (X%) in the SMW solution, in Fig. 7. As can be seen in this figure,
4. Conclusion In the foregoing two new etchants, NaOH/methanol and SMW solution have been systematically studied and reported. This study showed that 1.5 M NaOH/methanol solution at 55 ◦ C yield maximum value of etching efficiency (∼78%). Maximum efficiency was found to be ∼81% for SMW solution that consisted 60% methane, 10% NaOH and 30% water at 55 ◦ C. Both NaOH/methanol and SMW solutions are found to be more efficient than that of conventionally used 6 M aqueous NaOH (64%) at 70 ◦ C. Besides having higher etching efficiencies than 6 M NaOH (64%) at
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555 85 80
Efficiency (%)
75 70 65 60 55 50 40
50
60 70 Methanole (X%)
80
Fig. 7. Etching efficiency of CR-39 detector as a function of methanol concentration (X%) in SMW solution at 55 ◦ C.
70 ◦ C, Both NaOH/methanol and SMW solutions have the advantage that they require much less processing time when used as etchants.
References Bashir, A., Matiullah, Yang, X., Gul, M., 1993. Effect of presence of gamma rays with neutron fields on the performance of a CR39 based cubical neutron dosimeter. Nucl. Tracks Radiat. Meas. 22, 647–650. Benton, E.V., Richmond, R.G., 1986. Application of nuclear track detectors in space radiation dosimetry. Nucl. Tracks 12, 505–508. Brandt, R., 1993. Some recent applied and fundamental work with SSNTD. Nucl. Tracks Radiat. Meas. 21, 341–347. Cartwright, B.G., Shirk, E.K., Price, P.B., 1978. A nuclear track recording polymer of unique sensitivity and charge resolution. Nucl. Instrum. Methods B 153, 457–460.
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Durrani, S.A., Bull, R.K., 1987. Solid State Nuclear Track Detection: Principles, Methods and Applications, Pergamon Press, Oxford. Dwivedi, K.K., 1997. On the critical etching parameters of track detectors. Radiat. Meas. 27 (3), 453–456. Fleischer, R.L., Price, P.B., Walker, R.M., 1975. Nuclear Tracks in Solids: Principles and Applications, University of California Press, Berkeley. Henke, R., Ogura, K., Benton, E.V., 1986. Standard method for measurements of bulk etch rate in CR-39. Nucl. Tracks 12, 307–310. Khan, H.A., Manzoor, Matiullah, 1991. Interaction of 86 MeV/u—O and 107 MeV/u—C ions with different targets. Nucl. Tracks Radiat. Meas. 19, 639–640. Matiullah, 2000. Radiation Physics, Allama Iqbal Open University, Islamabad, Pakistan. Matiullah, Ahmed, A., Khan, G.A., Manzoor, S., Khan, H.A., 1988a. Some investigations on the response of CR-39 detector to protons deutrons and alpha particles. Nucl. Tracks Radiat. Meas. 15, 137–140. Matiullah, Durrani, S.A., Khan, G.A., 1988b. A practical fastneutron dosimeter based electrochemically etched CR-39 nuclear track detector with angle-independent response. Nucl. Instrum. Methods B 34, 499–504. Matiullah, Durrani, S.A., Kudo, K., 1990. A review of the use of CR-39 track detector in personnel neutron dosimetry and spectrometry. Nucl. Instrum. Methods B 51, 76–84. Matiullah, Kudo, K., Majeed, A., Fujii, M., 1991. Radon—a measure of living standard. Nucl. Tracks Radiat. Meas. 19 (1–4), 371–374. Matiullah, Tahiri, I.A., Subhani, M.S., Kudo, K., 2001. Improvement in the sample mass-change-method used for determination of VB of CR-39 neutron detector. Jpn. J. Appl. Phys. 40 (5A), 3474–3475. Matiullah, Rehman, S., Zaman, W., 2005. Discovery of new etchants for CR-39 detector. Radiat. Meas. 39 (3), 337–343. Qureshi, A.A., Khan, H.A., Tafail, M., Matiullah, 1991. Radon signals for geological explorations. Nucl. Tracks Radiat. Meas. 19, 383–384. Rashid, T., Matiullah, Gul, M., Yang, X., Bashir, A., 1993. Reassessment of the CR-39 based cubical neutron dosimeter. Nucl. Tracks Radiat. Meas. 22, 695–698. Tahiri, I.A., Matiullah, Subhani, M.S., 2003. Molten Ba(OH)2 · 8H2 O as an etchant for CR-39 detector. Radiat. Meas. 37, 205–210.
Short communication
Some more new etchants for CR-39 detector Matiullaha,∗ , S. Rehmana,1 , S. Rehmana,2 , N. Matib , S. Ahmadb a Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O.Nilore, Islamabad, Pakistan b Department of Physics, Government College Satellite Town, Rawalpindi, Pakistan
Received 30 August 2004; accepted 7 October 2004
Abstract Recently, several new etchants have been reported for CR-39 detector (Molten Ba(OH)2 . 8H2 O as an etchant for CR-39 detector, Radiat. Meas. 37 (2003) 205; Discovery of new etchants for CR-39 detector, Radiat. Meas. (2004)). We have made further progress in this direction and have unveiled two more new etchants which are reported in this article. CR-39 detectors were irradiated with fission fragments and alpha particles from a thin 252 Cf disc source. The irradiated detectors were then etched in our newly introduced etching solutions as well as in conventionally used 6 M NaOH aqueous solution at 70 ◦ C. The newly prepared etching solutions included NaOH dissolved in methanol and NaOH dissolved in methanol + water. Optimum values of NaOH concentration in methanol as well as in methanol + water were determined. Optimum etching temperatures were also determined for both the above-mentioned etchants. From fission and alpha track diameters, bulk etching rate (VB ), track etching rate (VT ) and etching efficiency () were determined and compared with that obtained for 6 M NaOH at 70 ◦ C. Both the newly introduced etchants were found more efficient than the conventionally used 6 M aqueous NaOH (64%) at 70 ◦ C and have relatively much smaller etching time. © 2004 Elsevier Ltd. All rights reserved. Keywords: Chemical etching; Processing time; NaOH/methanol; SMW solution; Etching efficiency
1. Introduction CR-39 is the most popular member of the SSNTD’s family (Cartwright et al., 1978). It has been widely used in many fields of science and technology (see, for example, Durrani and Bull, 1987; Fleischer et al., 1975; Matiullah et al., 1988a,b,1990,1991,2001; Khan et al., 1991; Rashid et al., 1993; Benton and Richmond, 1986; Brandt, 1993; Qureshi et al., 1991; Bashir et al., 1993; Matiullah, 2000; Dwivedi, 1997). Besides working on improving the quality ∗ Corresponding author. Tel.: +92 051 220 7380;
fax: +92 051 922 3727. E-mail address: [email protected] (Matiullah). 1 Shafi-ur-rehman. 2 Shakeel-ur-rehman. 1350-4487/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2004.10.009
of CR-39 detector, continuing efforts have been made to discover new etchants for which CR-39 detector have higher efficiency and shorter etching time. This is desirable because the chemical etching techniques reported for CR-39 detectors are time-consuming. Aqueous solutions of the hydroxides of alkali metals (group-IA) viz. NaOH and KOH have been extensively studied as etchants for CR-39 detector (see, for example Durrani and Bull, 1987). Tahiri et al. (2003) studied groupIIA metal-hydroxides such as Mg(OH)2 , Ca(OH)2 and Ba(OH)2 · 8H2 O, dissolved in distilled water. They have reported that molten Ba(OH)2 · 8H2 O is more efficient than that of 6 M NaOH aqueous solution. In addition to this, etching time is drastically reduced if molten Ba(OH)2 · 8H2 O is used as an etchant. Matiullah et al. (2005) went one step further and reported two more new etchants, namely
552
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555
NaOH/ethanol and NaOH/1-propanol. They found that 1 M NaOH/1-propanol solution at 49 ◦ C yields a maximum value of etching efficiency (∼70%). Whilst 1.5 M NaOH/ethanol yields maximum value of etching efficiency (∼77%) at 55 ◦ C. Both of the above-mentioned etchants are more efficient than the aqueous 6 M NaOH solution at 70 ◦ C. Like molten Ba(OH)2 · 8H2 O etching time is also drastically reduced when NaOH/ethanol and NaOH/1-propanol are used as etchants. We have now made further progress and have unveiled two more new etchants which are dealt with in this article. These include NaOH dissolved in methanol and NaOH dissolved in methanol + water (from now onward called SMW solution).
2. Experimental procedures CR-39 sheets of thickness 500 m, and supplied by Page Mouldings, Ltd., UK, were cut into small detectors of size 3 cm × 2.5 cm each. These detectors were irradiated with normally incident alpha particles and fission fragments from a thin source of 252 Cf. These detectors were then etched in NaOH/methanol and SMW solution at different concentrations and etching temperatures. After each etching step, detectors were washed under running water and then with distilled water. Diameters of the fission fragment and alpha particle tracks were measured under an optical microscope. Optimum values of etching temperature and concentration were determined. VB , VT and etching efficiency () were calculated using track diameter method (Henke et al., 1986; Matiullah et al., 2001). The values obtained for new etchants were compared with those obtained for CR-39 detectors etched in conventional 6 M aqueous solution of NaOH at 70 ◦ C.
3. Results and discussion Various concentrations of NaOH/methanol and SMW solutions were prepared. CR-39 detectors irradiated with fission fragments and alpha particles were etched in conventional 6 M aqueous solution of NaOH at 70 ◦ C and in the above-mentioned prepared NaOH/methanol as well as SMW solutions at different temperatures in order to achieve the optimum processing conditions for the newly introduced
etchants. From measured track diameters data, VB , VT and were determined using the following equations (Durrani and Bull, 1987): VB = Dff /2t,
(1)
VT = VB (1 + x 2 )/(1 − x 2 ),
(2)
= 1 − (VB /VT ),
(3)
V = VT /VB ,
(4)
where Dff represents average fission track diameter; D is the average alpha diameter; t is the etching time; is the track etching efficiency; V is the sensitivity and x =D /Dff . Table 1 shows the observed average track diameters, VB , VT and values for CR-39 detectors that were etched in the listed concentration of conventionally used NaOH solution at 70 ◦ C. As expected, both Dff and D are seen to increase with etchant concentration. About 6 M concentration yields the highest value of the efficiency (64%) which is in agreement with the experimental error with the published data (Durrani and Bull, 1987). 3.1. NaOH/methanol etchant Having verified already published etching parameters data for 6M NaOH at 70 ◦ C, we now present our data concerning determination of the optimum values of etchant concentration and temperature for NaOH dissolved in methanol. First, the effect of temperature was studied. To do so, CR39 detectors, irradiated with fission fragments and alpha particles, were etched in 1.5 M NaOH/methanol solution at different temperatures. There was not any special reason behind choosing the value 1.5 M of NaOH/methanol solution. In fact any other value would have also yielded similar results. Figs. 1 and 2 show average track diameters of fission fragments and alpha particles as a function of etching time for 1.5 M NaOH/methanol solution at the listed temperatures. As was expected, track diameter is seen to increase with an increase in the temperature of the etching solution. Initially, at lower values of the temperature (i.e. from 40 to 45 ◦ C), increase in the track diameter is negligibly small. Beyond 12 min etching time, increase in the track diameter becomes significant. It is clear from the above figures that at any etching time, higher values of the etching temperatures yield
Table 1 D , Dff , VB , VT and values of CR-39 detectors for the listed concentration of NaOH solution at 70 ◦ C Etchant conc. (M)
D (m)
Dff (m)
VB (m h−1 )
VT (m h−1 )
(%)
4 6 8 10 12
8 9.67 10.66 15 23
15 19.66 24 29.33 47.66
1 1.25 1.75 2.26 3.38
2.34 5 6.96 6.23 7.61
35.6 64 56.8 41.3 37.4
Fission fragment track diameter (µm)
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555
Table 2 VB , VT and etching efficiency of CR-39 detector for 1.5 M NaOH/methanol solution at the listed temperatures
55˚C 35 30 25
45˚C
20
553
50˚C 40˚C
15 10
Etchant temperature VB (◦ C) (m h−1 )
VT (m h−1 )
Sensitivity (v)
(%)
40 45 50 55 60
107.169 99.907 41.15 284.72 122.81
3.5714 2.831 4.33 4.55 3.78
72.00 64.68 76.91 78.04 73.5
30.007 35.28 9.5 62.5 32.43
5 2
4
6
8 10 12 14 Etching time (min)
16
18
20
22
80 78
Fig. 1. Average fission fragment track diameter as a function of etching time. Here CR-39 detectors were etched in 1.5 M NaOH dissolved in methanol at the listed temperatures.
76 Efficiency (%η)
74
30
Alpha track diameter (µm)
55°C
72 70 68 66 64
20
62
45°C 50°C
60 40°C
10
40
45 50 55 Etching Temperature (°C)
60
Fig. 3. Efficiency of CR-39 detector as a function of temperature for 1.5 M NaOH dissolved in methanol.
0 4
8
12 16 Etching time (min)
20
24
Fig. 2. Average alpha-particle track diameter as a function of etching time in CR-39 detectors etched in 1.5 M NaOH dissolved in methanol at the listed temperatures.
greater values of track diameters and hence higher VB and VT values. At 55 ◦ C, the track diameter increases steeply with an increase in the etching time. From these figures it may be clearly seen that only several minutes are required to have reasonable size of track diameters. This is a great advantage over 6 M NaOH aqueous solution where several hours of etching would have been required to get similar track diameters. From the measured track diameter data, VB , VT and were calculated. The results obtained are shown in Table 2. For clarity, the data shown in this table is plotted in Fig. 3. It can be seen in Fig. 3 that NaOH/methanol yields maximum value of (∼78%) at 55 ◦ C.
Having determined optimum etching temperature, we then studied the effect of concentration on the of CR-39 detector. Fig. 4 shows etching efficiency as a function of the etchant concentration. It is obvious from this figure that 1.5 M NaOH/methanol solution at 55 ◦ C yields maximum value of the efficiency. 3.2. NaOH/(methanol+water) etchant Our next newly discovered etchant is SMW solution. SMW is the solution that contains 10% NaOH dissolved in X% methanol and (90–X)% water. Since NaOH/methanol solution has maximum efficiency at 55 ◦ C (see Fig. 3), we used the same value of the temperature for SMW etchant. We then studied the effect of varying percentage of methanol in SMW solution on track diameters of alpha particles and fission fragments. Results obtained are plotted in Figs. 5 and 6 for the listed percentage values of methanol in SMW solution. Track diameter is seen to increase linearly with an increase in X value.
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555
80
60
75
50 Fission track diameter (µm)
Etching efficiency (%η )
554
70
65
60
55 1
1.25
1.5
1.75
X = 40 X = 50 X = 60 X = 70 X = 80
40
30
20
10
1.78
Etchant Conc.(mol l-1)
0
Fig. 4. Etching efficiency of CR-39 detector as a function of NaOH/methanol concentration at 55 ◦ C.
8
12 16 Etching time (min)
20
Fig. 6. Average track diameter of fission fragments as a function of methanol concentration (X%) in SMW solution at 55 ◦ C.
40
Table 3 VB , VT and etching efficiency of CR-39 detector for the listed concentrations of methanol (X%) in SMW Solution at 55 ◦ C
X = 40 X = 50 X = 60 X = 70 X = 80
30 Alpha track diameter (µm)
4
20
Methanol (X%)
VB (m m−1 )
VT (m m−1 )
Sensitivity (v)
(%)
40 50 60 70 80
0.1875 0.594 0.71 1.292 1.166
0.487 1.639 3.7 6.092 3.596
2.6 2.76 5.212 4.715 3.082
61.5 63.76 80.81 78.79 67.54
10
maximum efficiency (∼81%) is achieved at 60% methanol concentration in SMW solution, i.e. optimum percentage ratio of methanol/water lies around 60/30 with 10% NaOH. 0 4
8
12 16 Etching time (min)
20
Fig. 5. Average track diameter of alpha particles as a function of methanol concentration (X%) in SMW solution at 55 ◦ C.
From measured track diameter data, shown in Figs. 5 and 6, VB , VT and were calculated which are shown in Table 3. For greater clarity, etching efficiency () shown in Table 3 is plotted as a function of methanol concentration (X%) in the SMW solution, in Fig. 7. As can be seen in this figure,
4. Conclusion In the foregoing two new etchants, NaOH/methanol and SMW solution have been systematically studied and reported. This study showed that 1.5 M NaOH/methanol solution at 55 ◦ C yield maximum value of etching efficiency (∼78%). Maximum efficiency was found to be ∼81% for SMW solution that consisted 60% methane, 10% NaOH and 30% water at 55 ◦ C. Both NaOH/methanol and SMW solutions are found to be more efficient than that of conventionally used 6 M aqueous NaOH (64%) at 70 ◦ C. Besides having higher etching efficiencies than 6 M NaOH (64%) at
Matiullah et al. / Radiation Measurements 39 (2005) 551 – 555 85 80
Efficiency (%)
75 70 65 60 55 50 40
50
60 70 Methanole (X%)
80
Fig. 7. Etching efficiency of CR-39 detector as a function of methanol concentration (X%) in SMW solution at 55 ◦ C.
70 ◦ C, Both NaOH/methanol and SMW solutions have the advantage that they require much less processing time when used as etchants.
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