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A new simple method to study the induction time
Nuclear Instruments and Methods in Physics Research B 103 (1995) 79-82
Beam Interactions with Materials & Atoms
ELSEVIER
A new simple method to study the induction time R. Mazzei a, *, D. Schinca b,1 a Comision Nacional de Energia Atomica (CNEA), Av. del Libertador 8250, Buenos Aires, Argentina b Centro de bwestigaciones Opticas (CIOp), (CON[CET-CICBA), casilla de correo 124, 1900 La Plata, Argentina
Received 14 February 1995; revised form received 3 April 1995 Abstract In the present work, an easy automatic method based on foil laser scattering measurements is applied to evaluate the induction time (ti) in CR-39 solid state nuclear track detectors for different etching temperatures. A quantity q, proportional to the amount of suface layer removed is plotted against etching temperature. The experimental results are compared with those obtained from microspectrophotometer measurements for Macrofol-E detectors.
1. Introduction The time evolution of track diameter and track length vs. etching time indicates that tracks become observable only after a certain time from the beginning of the etching process - induction time - [1-5]. Usually, the induction time is found by extrapolating the intersection of the resulting curves with the time axis. Rudy et al. [4] observed that according to Blandford data [6] the bulk velocity at 50°C is ten times greater than the bulk velocity at 30°C, and extrapolating from Baroni data [7] they showed that the induction time at 50°C is ten times shorter than the induction time at 30°C. Further, Grabez et al. [8] showed for CR-39 detector that the assumption of Rudy et al. [4] about temperature dependence of induction time is supported by their results i.e.: the lower the temperature, the larger the value of the induction time. Moreover, Schlenk et al. [9] showed that the empirical data of the bulk velocity vs. the etching temperature can be well described by the Arrhenius correlation Vb cr e x p ( - E o / k T ) where k is the Boltzmann constant, T the temperature of the etchant in K and E o is the activation energy of the etching process. So, the quantity: (Const. × exp(-Eo/kT)) × (induction time (ti)) should remain independent of the temperature. In the following, we will use this quantity instead of induction time to construct the graphics. In most papers on induction time, the data are obtained by means of optical microscopy [2-5] or electron microscopy [1], involving time-consuming measurements. On
* Corresponding author. Fax +54 1 703 2645. 1 Member of Comision Investigaciones Cientificas Buenos Aires.
the other hand, an easy method based on light transmission measurement has been applied to evaluate the induction time [10]. This method uses the light scattering track properties: the elastic scattering of light by small objects (tracks) is strongly dependent upon size, shape, orientation and refractive index of the particle, as well as on the wavelength of the light [11]. However, the evaluation of the induction time vs. temperature curve again involve several foils and excessive tedious measurements. For this reason an automatic method based on foil laser light scattering measurements is presented and applied to evaluate the induction time in Cr-39 for a Pew solution at different etching temperatures. On the other hand, the method shown in Ref. [10] was used to evaluate the induction time in Macrofol-E for a Pew solution at different etching temperatures. The results obtained using the above methods are compared among them and with those obtained by other authors.
2. Materials and methods
Macrofol-E foils (300 ~m thickness) and CR-39 foils (100 ~m thickness) were used as SSNTD. Irradiations were performed with a 252Cf source in a 2w geometry, for irradiation time of 4 days in Macrofol-E and 0.5, 1, and 5 h and 6 days in CR-39 (highly satured latent track foils). The foils were processed with a Pew solution (30 g KOH + 80 g ethyl alcohol + 90 g HeO) for etching temperatures varying between - 1 ° C and 46°C. The light transmission of the Macrofol foils was measured with a Microspectrophotometer Zeiss M4 Q III, using a white light source. Mean values of light transmission in nonirradiated (I o) and irradiated areas (I) of the foils were obtained from 30 to 50 measurements in each region.
0168-583X/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0168-583X(95)00561-7
80
R. Mazzei, D. Schinca /Nucl. Instr. and Meth. in Phys. Res. B 103 (1995) 79-82
TranmmlmmlonVe. etching time IIio len~e~ l%
l>Lf ToN ¢ellectmg
pri~rn
pholodiode ~
ophcal fibre C
og'eI
'x~ tl
p~ 0.9
Fig, 1. Experimental setup.
0.85
0.8
~ e
To perform continuous etch of the CR-39 foils, an etch bath was constructed. The water circulating in a cavity around the etch bath was pumped from a few liter reservoir in a constant temperature bath into the cavity by a small pump and then returned to the reservoir (Fig. 1). Simultaneously to the CR-39 etching process a 2 mW He-Ne laser beam passed through the foil and the light scattered by it was collected by a fiber optic bundle placed at a suitable angle and measured with a RCA 931 photomultiplier with an $2 type photocathode surface. The output current of the photomultiplier was passed through a current to voltage converter and then fed into a signal comparator which divided the light scattering signal by a reference light signal coming from the He-Ne source through a photodiode. Finally, this normalized output was fed into a plotter.
3. Results 3.1. Microspectrophotometer measurements
Fig. 2 shows the ratio I / I o vs. the etching time for 44°C for Macrofol-E foils. Similar figures can be obtained for other temperatures. After the induction time the tracks develop and begin to scatter the light. So the I / I o vs. etching time curve starts to decrease and forms a shoulder, which is a reliable estimate of the induction time, since selected irradiation time (4 days) warrants the overlapping of the tracks in the damage zone [10]. Moreover, in Refs. [8,9] it is shown that a superficial layer h = Vbt must be removed before the track begins to develop. In Fig. 3, the quantity q = [Vb(T°C)ti(T°C)I/[Vu(- l°C)ti(- l°C)] (with Vb c~ exp(-Eo/kT)), which is proportional to Vbt i is plotted against temperature. This figure shows an oscillatory behaviour of q around a mean value of = 0.5. The peak to peak amplitude of the oscillations is twice the mean value. These fluctuations are greater than those we can attribute as coming from experimental errors as shown by the error bars in the figure.
i
1o
i to
,
=o Etching time(moo)
~ =o
8o 1I,
Fig. 2. Quotient between transmission in damage and non-damage zone.
3.2. Laser automatic measurements
Fig. 1 shows our experimental arrangement used for the continuous etching of the CR-39 foils, Figs, 4 and 5 show the intensity of the foil dispersed light as a function of the chemical etching time. Fig. 4 is for a 40°C bath and the arrow indicates the time (aproximately 25 s) for which the tracks start to scatter the light. The criterion used in this case is to take as the induction time the point at which the curve starts to depart from background noise, This time is a reliable estimate of the induction time, since selected irradiation time (6 days) warrants the overlapping of the tracks in the damage zone [1,10]. This is the result of a collective scattering effect of tracks with radius less than 500 A - new born tracks - . The two peaks shown in this figure were also observed for other etching temperatures. Fig. 5 was obtained in a similar way for 26°C, The induction time varies from about 25 s at 40°C to about 150 s at 26°C [4].
125 MACI~FOL
1 0.75' 0,5 025 o
-tO
I0 ~F..~R.AT
UII.E (*C)
Fig. 3. Parameter q (proportional to Vbti) vs. etching temperature for Macrofol-E. The experimental points were obtained using the microspectrophotometer technique,
R. Mazzei, D. Schinca /Nucl. h~str, and Meth. in Phys. Res. B 103 (1995) 79-82
~
81
TIME(see)
Fig. 4. Laser scattering intensity vs. etching time for CR-39 with a 40°C temperature bath. The arrow indicates the induction time. The peaks corresponding to fission fragments and alpha particles are clearly resolved.
Fig. 6 shows q as a function of the etching temperature for CR-39. An oscillatory behaviour of q is again observed. These fluctuations are greater than those which can be attributed as coming from experimental errors, as shown by the error bars in the figure. Fig. 7 was obtained for 1 / 2 (a) and 5 h (b) irradiation time with ~2Cf. In both cases, the etching process was interrupted at the positions indicated by the vertical lines. The foils were removed from the bath, carefully washed with distilled water and smoothly dried before repositioning them in the etching bath. No discontinuity in the slope of the curves at the interruption points was observed. The process seemed to develop in a continuous way independent of the removal of the foils.
~2~
TIME(see)
Fig. 5. Laser scattering intensity vs. etching time for CR-39 with a 26°C temperature bath.
i]
CR-39
\
q 4 3' 2~ 1 0 10
25~ 20
30 TEMPERATURE (.C)
40
Fig. 6. Parameter q (proportional to Vbti) vs. etching temperature for CR-39. The experimental points were obtained using the laser automatic technique.
TI~ (se~)
Fig. 7. Laser scattering intensity vs. etching time for CR-39 with a 40°C temperature bath. (a) 5 h irradiation foil; (b) h~ilf an hour irradiation foil. The vertical lines indicate the interruption of the etching process. Note the continuity of the curve and its slope at these points.
82
R. Mazzei, D. Schinca /Nucl. Instr. and Meth. in Phys. Res. B 103 (1995) 79-82
4. Discussion
Due to the large ratio between the etching velocity in the damage region and the velocity in the non-damage region (around 104), the chemical bath reaches the range corresponding to the fission fragments (between 20 and 25 p.m) immediately after the induction time, and the damage region becomes completely removed by that time. As the chemical attack proceeds, the track dimensions increase and the scattering intensity keeps growing. On the other hand, after a certain time, which depends on the etching temperature and foil irradiation time, the tracks begin to overlap, generating large zones which scatter light poorly. In this way, the intensity curve starts to decrease (first peak). The 257"Cf source emits also alpha particles with ranges of approximately 40 Ixm (twice that of the fission fragments). These tracks have both an attack velocity much smaller than that corresponding to the fission fragments, yielding smaller tracks, and on the other hand, they have larger ranges, which determine that the chemical attack takes a larger time to reach the end of the particle trajectory. Both effects contribute to an increase in the scattering intensity for times longer than the one corresponding to the fission fragments. Thus, the curve shows two peaks, one due to the alpha particles and the other due to the fission fragments. In Figs. 7a and To it can be seen that the time for which the foil starts to scatter light (150 and 225 s respectively) is much larger than that corresponding to the 6 days irradiation foil (around 25 s). This is due to the fact that, since the number of tracks is proportional to the irradiation time, the fraction of scattering zone, for the same etching time, is less for decreasing irradiation times. Besides, for the same irradiation time, the fraction of scattering zone increases for increasing etching time. Thus, the chemical process needs to act upon the damage zone for a longer period to create track dimensions that may yield similar light scattering in the foil. This effect has been observed using the method described in Ref. [10], when the dead time is plotted against the irradiation time. It is then observed that the dead time aproximates asymptotically to a minimum for irradiation times in excess of 2 days (induction time). For these times, the damage created by the different particles overlap with each other and the induction time in this case coincides with the time taken for the tracks to develop. However, for irradiation times such that track damages do not overlap, it is necessary to chemically act upon the foil for a longer period to obtain the same effect. This is observed in Fig. 7, where tirrad (Fig. 7a) is larger than tir,ad (Fig. To) and tdead (Fig. 7a) is lesser than tdead (Fig. To). Another feature that can be seen from Fig. 7, is that interruption of the chemical process for tracks with diameter larger than the damage zone produces neither a dead time nor a change in the slope of the curve when the process is restarted. Similar features were ob-
tained for 1 and 5.5 h irradiation time. This fact suggests that the velocity of the chemical attack outside the damage zone (Vb) after the interruption takes instantaneously its previous value. Since here is an induction time during which the tracks do not develop, it can be concluded that Vt-- Vb for etching times less than the induction time.
5. Conclusions As it can be seen both from Macrofol-E microspectrophotometer measurements and from CR-39 laser automatic measurements, the quantity q presents an oscillatory behaviour when plotted against etching temperature. So, it can be concluded that the induction time is not inversely proportional to the bulk velocity (Vu). For CR-39, the attack velocity in the bulk region reaches its value Vu instantaneously. Moreover, for etching times less than the induction time, the track and bulk velocities must be equal. If they were not, the laser light would be scattered by the holes or tips produced by the chemical etching process. The laser 'automatic measurements presented in this work yield induction times which compare well with times evaluated by other methods. We will use this method to determine the induction time for a variety of SSNTD with different etching solutions at different temperatures and for several types of ions and energies. In this way, we should obtain relevant information about the characteristics of the induction time and its production mechanisms.
References
[1] J.C. Bourdin, R. Mazzei, O.A. Bernaola, J.C. Grasso and G. Saint Martin, Nucl. Instr. and Meth. B 28 (1987) 548. [2] H.B. Luck, Nucl. Instr. and Meth. 131 (1975) 105. [3] F.H. Rudy, H.B.Knowless and G.E. Tripard, Phys. Rev. Lett. 37 (1976) 826. [4] F.H. Rudy, H.B. Knowless, S.C. Luckstead and G.E. Tripard, Nucl. Instr. and Meth. 147 (1977) 25. [5] P. Schwenck, G. Sermund and W. Enge, Nucl. Tracks 8 (1984) 37. [6] G.E. Blandford, R.M. Walker and J.P. Weel, Radiat. Eft. 3 (1970) 267. [7] G. Baroni, S.D. Liberto, G. Romano, C. Sgarbi and M.C. Tabasso, Nucl. Instr. and Meth. 98 (1973) 221. [8] B. Gravez, P. Vater and R. Brandt, Nuel. Tracks 5 (3) (1981) 291. [9] B. Schlenk, G. Somogyi and A. Valek, Radiat. Eft. 24 (1975) 247. [10] O.A. Bernaola, R. Mazzei, G. Saint Martin and J.C. Grasso, Nucl. Tracks Radiat. Meas. 15 (1-4) (1988) 141. [11] P.J. McNulty, S.R. Palmer and D.D. Cooke, Proc. llth. Int. Conf. on SSN'TD,Bristol, 1981, eds. P.H. Fowler and V.M. Clapham (Pergamon, Oxford, 1982) p. 807.
Beam Interactions with Materials & Atoms
ELSEVIER
A new simple method to study the induction time R. Mazzei a, *, D. Schinca b,1 a Comision Nacional de Energia Atomica (CNEA), Av. del Libertador 8250, Buenos Aires, Argentina b Centro de bwestigaciones Opticas (CIOp), (CON[CET-CICBA), casilla de correo 124, 1900 La Plata, Argentina
Received 14 February 1995; revised form received 3 April 1995 Abstract In the present work, an easy automatic method based on foil laser scattering measurements is applied to evaluate the induction time (ti) in CR-39 solid state nuclear track detectors for different etching temperatures. A quantity q, proportional to the amount of suface layer removed is plotted against etching temperature. The experimental results are compared with those obtained from microspectrophotometer measurements for Macrofol-E detectors.
1. Introduction The time evolution of track diameter and track length vs. etching time indicates that tracks become observable only after a certain time from the beginning of the etching process - induction time - [1-5]. Usually, the induction time is found by extrapolating the intersection of the resulting curves with the time axis. Rudy et al. [4] observed that according to Blandford data [6] the bulk velocity at 50°C is ten times greater than the bulk velocity at 30°C, and extrapolating from Baroni data [7] they showed that the induction time at 50°C is ten times shorter than the induction time at 30°C. Further, Grabez et al. [8] showed for CR-39 detector that the assumption of Rudy et al. [4] about temperature dependence of induction time is supported by their results i.e.: the lower the temperature, the larger the value of the induction time. Moreover, Schlenk et al. [9] showed that the empirical data of the bulk velocity vs. the etching temperature can be well described by the Arrhenius correlation Vb cr e x p ( - E o / k T ) where k is the Boltzmann constant, T the temperature of the etchant in K and E o is the activation energy of the etching process. So, the quantity: (Const. × exp(-Eo/kT)) × (induction time (ti)) should remain independent of the temperature. In the following, we will use this quantity instead of induction time to construct the graphics. In most papers on induction time, the data are obtained by means of optical microscopy [2-5] or electron microscopy [1], involving time-consuming measurements. On
* Corresponding author. Fax +54 1 703 2645. 1 Member of Comision Investigaciones Cientificas Buenos Aires.
the other hand, an easy method based on light transmission measurement has been applied to evaluate the induction time [10]. This method uses the light scattering track properties: the elastic scattering of light by small objects (tracks) is strongly dependent upon size, shape, orientation and refractive index of the particle, as well as on the wavelength of the light [11]. However, the evaluation of the induction time vs. temperature curve again involve several foils and excessive tedious measurements. For this reason an automatic method based on foil laser light scattering measurements is presented and applied to evaluate the induction time in Cr-39 for a Pew solution at different etching temperatures. On the other hand, the method shown in Ref. [10] was used to evaluate the induction time in Macrofol-E for a Pew solution at different etching temperatures. The results obtained using the above methods are compared among them and with those obtained by other authors.
2. Materials and methods
Macrofol-E foils (300 ~m thickness) and CR-39 foils (100 ~m thickness) were used as SSNTD. Irradiations were performed with a 252Cf source in a 2w geometry, for irradiation time of 4 days in Macrofol-E and 0.5, 1, and 5 h and 6 days in CR-39 (highly satured latent track foils). The foils were processed with a Pew solution (30 g KOH + 80 g ethyl alcohol + 90 g HeO) for etching temperatures varying between - 1 ° C and 46°C. The light transmission of the Macrofol foils was measured with a Microspectrophotometer Zeiss M4 Q III, using a white light source. Mean values of light transmission in nonirradiated (I o) and irradiated areas (I) of the foils were obtained from 30 to 50 measurements in each region.
0168-583X/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0168-583X(95)00561-7
80
R. Mazzei, D. Schinca /Nucl. Instr. and Meth. in Phys. Res. B 103 (1995) 79-82
TranmmlmmlonVe. etching time IIio len~e~ l%
l>Lf ToN ¢ellectmg
pri~rn
pholodiode ~
ophcal fibre C
og'eI
'x~ tl
p~ 0.9
Fig, 1. Experimental setup.
0.85
0.8
~ e
To perform continuous etch of the CR-39 foils, an etch bath was constructed. The water circulating in a cavity around the etch bath was pumped from a few liter reservoir in a constant temperature bath into the cavity by a small pump and then returned to the reservoir (Fig. 1). Simultaneously to the CR-39 etching process a 2 mW He-Ne laser beam passed through the foil and the light scattered by it was collected by a fiber optic bundle placed at a suitable angle and measured with a RCA 931 photomultiplier with an $2 type photocathode surface. The output current of the photomultiplier was passed through a current to voltage converter and then fed into a signal comparator which divided the light scattering signal by a reference light signal coming from the He-Ne source through a photodiode. Finally, this normalized output was fed into a plotter.
3. Results 3.1. Microspectrophotometer measurements
Fig. 2 shows the ratio I / I o vs. the etching time for 44°C for Macrofol-E foils. Similar figures can be obtained for other temperatures. After the induction time the tracks develop and begin to scatter the light. So the I / I o vs. etching time curve starts to decrease and forms a shoulder, which is a reliable estimate of the induction time, since selected irradiation time (4 days) warrants the overlapping of the tracks in the damage zone [10]. Moreover, in Refs. [8,9] it is shown that a superficial layer h = Vbt must be removed before the track begins to develop. In Fig. 3, the quantity q = [Vb(T°C)ti(T°C)I/[Vu(- l°C)ti(- l°C)] (with Vb c~ exp(-Eo/kT)), which is proportional to Vbt i is plotted against temperature. This figure shows an oscillatory behaviour of q around a mean value of = 0.5. The peak to peak amplitude of the oscillations is twice the mean value. These fluctuations are greater than those we can attribute as coming from experimental errors as shown by the error bars in the figure.
i
1o
i to
,
=o Etching time(moo)
~ =o
8o 1I,
Fig. 2. Quotient between transmission in damage and non-damage zone.
3.2. Laser automatic measurements
Fig. 1 shows our experimental arrangement used for the continuous etching of the CR-39 foils, Figs, 4 and 5 show the intensity of the foil dispersed light as a function of the chemical etching time. Fig. 4 is for a 40°C bath and the arrow indicates the time (aproximately 25 s) for which the tracks start to scatter the light. The criterion used in this case is to take as the induction time the point at which the curve starts to depart from background noise, This time is a reliable estimate of the induction time, since selected irradiation time (6 days) warrants the overlapping of the tracks in the damage zone [1,10]. This is the result of a collective scattering effect of tracks with radius less than 500 A - new born tracks - . The two peaks shown in this figure were also observed for other etching temperatures. Fig. 5 was obtained in a similar way for 26°C, The induction time varies from about 25 s at 40°C to about 150 s at 26°C [4].
125 MACI~FOL
1 0.75' 0,5 025 o
-tO
I0 ~F..~R.AT
UII.E (*C)
Fig. 3. Parameter q (proportional to Vbti) vs. etching temperature for Macrofol-E. The experimental points were obtained using the microspectrophotometer technique,
R. Mazzei, D. Schinca /Nucl. h~str, and Meth. in Phys. Res. B 103 (1995) 79-82
~
81
TIME(see)
Fig. 4. Laser scattering intensity vs. etching time for CR-39 with a 40°C temperature bath. The arrow indicates the induction time. The peaks corresponding to fission fragments and alpha particles are clearly resolved.
Fig. 6 shows q as a function of the etching temperature for CR-39. An oscillatory behaviour of q is again observed. These fluctuations are greater than those which can be attributed as coming from experimental errors, as shown by the error bars in the figure. Fig. 7 was obtained for 1 / 2 (a) and 5 h (b) irradiation time with ~2Cf. In both cases, the etching process was interrupted at the positions indicated by the vertical lines. The foils were removed from the bath, carefully washed with distilled water and smoothly dried before repositioning them in the etching bath. No discontinuity in the slope of the curves at the interruption points was observed. The process seemed to develop in a continuous way independent of the removal of the foils.
~2~
TIME(see)
Fig. 5. Laser scattering intensity vs. etching time for CR-39 with a 26°C temperature bath.
i]
CR-39
\
q 4 3' 2~ 1 0 10
25~ 20
30 TEMPERATURE (.C)
40
Fig. 6. Parameter q (proportional to Vbti) vs. etching temperature for CR-39. The experimental points were obtained using the laser automatic technique.
TI~ (se~)
Fig. 7. Laser scattering intensity vs. etching time for CR-39 with a 40°C temperature bath. (a) 5 h irradiation foil; (b) h~ilf an hour irradiation foil. The vertical lines indicate the interruption of the etching process. Note the continuity of the curve and its slope at these points.
82
R. Mazzei, D. Schinca /Nucl. Instr. and Meth. in Phys. Res. B 103 (1995) 79-82
4. Discussion
Due to the large ratio between the etching velocity in the damage region and the velocity in the non-damage region (around 104), the chemical bath reaches the range corresponding to the fission fragments (between 20 and 25 p.m) immediately after the induction time, and the damage region becomes completely removed by that time. As the chemical attack proceeds, the track dimensions increase and the scattering intensity keeps growing. On the other hand, after a certain time, which depends on the etching temperature and foil irradiation time, the tracks begin to overlap, generating large zones which scatter light poorly. In this way, the intensity curve starts to decrease (first peak). The 257"Cf source emits also alpha particles with ranges of approximately 40 Ixm (twice that of the fission fragments). These tracks have both an attack velocity much smaller than that corresponding to the fission fragments, yielding smaller tracks, and on the other hand, they have larger ranges, which determine that the chemical attack takes a larger time to reach the end of the particle trajectory. Both effects contribute to an increase in the scattering intensity for times longer than the one corresponding to the fission fragments. Thus, the curve shows two peaks, one due to the alpha particles and the other due to the fission fragments. In Figs. 7a and To it can be seen that the time for which the foil starts to scatter light (150 and 225 s respectively) is much larger than that corresponding to the 6 days irradiation foil (around 25 s). This is due to the fact that, since the number of tracks is proportional to the irradiation time, the fraction of scattering zone, for the same etching time, is less for decreasing irradiation times. Besides, for the same irradiation time, the fraction of scattering zone increases for increasing etching time. Thus, the chemical process needs to act upon the damage zone for a longer period to create track dimensions that may yield similar light scattering in the foil. This effect has been observed using the method described in Ref. [10], when the dead time is plotted against the irradiation time. It is then observed that the dead time aproximates asymptotically to a minimum for irradiation times in excess of 2 days (induction time). For these times, the damage created by the different particles overlap with each other and the induction time in this case coincides with the time taken for the tracks to develop. However, for irradiation times such that track damages do not overlap, it is necessary to chemically act upon the foil for a longer period to obtain the same effect. This is observed in Fig. 7, where tirrad (Fig. 7a) is larger than tir,ad (Fig. To) and tdead (Fig. 7a) is lesser than tdead (Fig. To). Another feature that can be seen from Fig. 7, is that interruption of the chemical process for tracks with diameter larger than the damage zone produces neither a dead time nor a change in the slope of the curve when the process is restarted. Similar features were ob-
tained for 1 and 5.5 h irradiation time. This fact suggests that the velocity of the chemical attack outside the damage zone (Vb) after the interruption takes instantaneously its previous value. Since here is an induction time during which the tracks do not develop, it can be concluded that Vt-- Vb for etching times less than the induction time.
5. Conclusions As it can be seen both from Macrofol-E microspectrophotometer measurements and from CR-39 laser automatic measurements, the quantity q presents an oscillatory behaviour when plotted against etching temperature. So, it can be concluded that the induction time is not inversely proportional to the bulk velocity (Vu). For CR-39, the attack velocity in the bulk region reaches its value Vu instantaneously. Moreover, for etching times less than the induction time, the track and bulk velocities must be equal. If they were not, the laser light would be scattered by the holes or tips produced by the chemical etching process. The laser 'automatic measurements presented in this work yield induction times which compare well with times evaluated by other methods. We will use this method to determine the induction time for a variety of SSNTD with different etching solutions at different temperatures and for several types of ions and energies. In this way, we should obtain relevant information about the characteristics of the induction time and its production mechanisms.
References
[1] J.C. Bourdin, R. Mazzei, O.A. Bernaola, J.C. Grasso and G. Saint Martin, Nucl. Instr. and Meth. B 28 (1987) 548. [2] H.B. Luck, Nucl. Instr. and Meth. 131 (1975) 105. [3] F.H. Rudy, H.B.Knowless and G.E. Tripard, Phys. Rev. Lett. 37 (1976) 826. [4] F.H. Rudy, H.B. Knowless, S.C. Luckstead and G.E. Tripard, Nucl. Instr. and Meth. 147 (1977) 25. [5] P. Schwenck, G. Sermund and W. Enge, Nucl. Tracks 8 (1984) 37. [6] G.E. Blandford, R.M. Walker and J.P. Weel, Radiat. Eft. 3 (1970) 267. [7] G. Baroni, S.D. Liberto, G. Romano, C. Sgarbi and M.C. Tabasso, Nucl. Instr. and Meth. 98 (1973) 221. [8] B. Gravez, P. Vater and R. Brandt, Nuel. Tracks 5 (3) (1981) 291. [9] B. Schlenk, G. Somogyi and A. Valek, Radiat. Eft. 24 (1975) 247. [10] O.A. Bernaola, R. Mazzei, G. Saint Martin and J.C. Grasso, Nucl. Tracks Radiat. Meas. 15 (1-4) (1988) 141. [11] P.J. McNulty, S.R. Palmer and D.D. Cooke, Proc. llth. Int. Conf. on SSN'TD,Bristol, 1981, eds. P.H. Fowler and V.M. Clapham (Pergamon, Oxford, 1982) p. 807.