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Polymerizing condition of DAP resin as fission track detector
Radiation Measurements 35 (2002) 171 – 175
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Polymerizing condition of DAP resin as $ssion track detector Y. Koguchi ∗ , T. Tsuruta Atomic Energy Research Institute, Kinki University, Kowakae, Higashi-Osaka, 577-8502, Japan Received 31 October 2001; received in revised form 14 December 2001; accepted 22 January 2002
Abstract Three kinds of diallyl phthalate resin plates were cast under di1erent polymerizing conditions. The plates were irradiated with $ssion fragments, -particles, fast and thermal neutrons. After irradiation, the plates were etched with an aqueous solution or a PEW solution. After etching, enlarged nuclear tracks on the plates were observed and counted using an optical microscope. All plates were found to have high detection e6ciency for $ssion fragments, but to be insensitive to -particles, fast and thermal neutrons. The etching speed of $ssion tracks on under-cured plates was faster than that on full- and over-cured plates whichever etching solution was used. In the case of adopting the aqueous solution, surface roughness occurs remarkably on the full- and over-cured plates in comparison with the under-cured plates. From these experimental results the conclusion was c 2002 Elsevier drawn that the under-cured plate was superior to the full- and over-cured plates as $ssion track detector. Science Ltd. All rights reserved. Keywords: Polymerization condition; DAP resin; Diallyl phthalate; Nuclear track detector; Fission fragment; -particle; Fast and thermal neutrons; PEW solution; Under-, full- or over-curing
1. Introduction Diallyl phthalate (DAP) resin is a thermosetting plastic. The resin is widely used as parts in electrical devices, precision apparatus, aircraft and building materials, since it is excellent with regard to heat, chemical and insulating resistance, and dimensional stability. In addition, the resin is used as spectacle lenses because of its high refractive index and appropriate hardness. The ortho-type DAP resin plate has a detection e6ciency of about 100% for $ssion fragments of both perpendicular and random incidence. However, the plate is insensitive to -particles and fast neutrons. (Tsuruta, 1999). This property is suitable for detecting selected $ssion fragments, which sometimes coexist with -particles or fast neutrons. In the case of the etching with aqueous solution of KOH, an etching time of 2– 4 hours (h) is required in order to obtain etch-pits of appropriate size for counting. In order to reduce the etching time, we tried PEW solution containing
∗
Corresponding author. Fax: +81-6-6721-3743. E-mail address: [email protected] (Y. Koguchi).
KOH, ethanol and water. The PEW solution had been used for the etching of polycarbonate (Somogyi et al., 1977) and CR-39 resin (Somogyi and Hunyadi, 1979). It was found that PEW solution made the etching time for DAP resin less than one-tenth of the etching time using aqueous solution (Tsuruta, 2001b). It is the purpose of this study to $nd suitable polymerizing conditions in order to obtain the DAP resin plates possessing a suitable etching time and smooth surface after etching for use in nuclear track detection.
2. Materials and methods 2.1. Casting of the plates The main constituent of the plates was the ortho-type DAP. The diisopropyl peroxy dicarbonate (IPP) was added at a concentration of 3% as a polymerizing initiator. The DAP solution mixed with IPP was poured into sandwich moulds, which was made up of two parallel Hat glasses and an elasticated gasket. The moulds containing the mixture were placed in an electric oven and treated with three kinds
c 2002 Elsevier Science Ltd. All rights reserved. 1350-4487/02/$ - see front matter PII: S 1 3 5 0 - 4 4 8 7 ( 0 2 ) 0 0 0 4 4 - 6
172
Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175
of UTR-KINKI. The thermal neutron Huence was obtained by measuring the activity of irradiated Au foils. 2.4. Etching and observation of etch-pits After irradiation, one group of the plates was etched in ◦ an aqueous solution of 30% KOH at 90 C. The etching time was from 30 min to 16 h. Another group of plates was etched in a PEW solution, which consisted of 15% KOH, ◦ 65% ethanol and 20% water, and was maintained at 60 C. The etching time was from 4 to 60 min. The solution was agitated by magnetic-driven vanes during etching. After etching, the plates were immediately washed clean in cold Howing tap water and dried under clean ventilation. The shape of the etch-pits was observed, and the number of the etch-pits was counted using an optical microscope. Fig. 1. Three kinds of thermal histories for polymerization of DAP resin plates.
of heat histories as shown in Fig. 1. When the temperature ◦ ◦ dropped to 50 C or 70 C, the newly formed plates were removed from the moulds. The periods of heat treatment for curing were about 27, 49 or 74 h. The 49 h curing was considered to be a standard condition for full polymerization in the manufacturing process of spectacle lenses. Therefore, we named the 27, 49 and 74 h curing plates, respectively, under-, full- and over-cured plates. Three kinds of colorless, transparent plates were formed which were 550 mm ×550 mm and 1:6 mm thick. All plates were able to be cut easily with a plastic cutter. The rectangular plates of about 30 mm × 10 mm were used for the following experiments. 2.2. Irradiation of 2ssion fragments and -particles The $rst set of the plates were arranged horizontally parallel to an electro-deposited plane standard source of Cf-252. The density of incident particles was calculated from the disintegration rate and radius of the source, the distance between the source and the plate and the irradiation time. The distance was set at pre-selected 1 cm. Fission fragments and -particles were slowed down by air, and hit the surface almost perpendicularly, because the radius of the source is small (Tsuruta, 2000). 2.3. Irradiation of fast and thermal neutrons The second set of the plates was irradiated with fast neutrons from a Pu–Be source, which was utilized to obtain several MeV neutrons. The fast neutron Huence was calculated from the source intensity, distance between the source and the plate, and the irradiation time. The third set of the plates was irradiated with thermal neutrons from a reactor
3. Experimental results Figs. 2 and 3 reveal the transition in the shape of etch-pits on the three kinds of plates which were irradiated with $ssion fragments and -particles. The plates of Figs. 2 and 3 were etched using the aqueous solution and the PEW solution, respectively. In Figs. 2 and 3, a series of photographs arranged lengthwise represents the transition of the same area of a plate at successive stages of etching. From a comparison between the density of the etch-pits and the density of incident particles, we recognized that the etch-pits which appeared were caused by the $ssion fragments. The detection e6ciency of the $ssion fragments was almost 100%. The etch-pits caused by -particle, fast and thermal neutron irradiation could not be found for the three kinds of plates under the above-mentioned etching conditions. In the case of Fig. 2(1), a relatively smooth surface is maintained for up to 8 h of etching time. However, in the case of Figs. 2(2) and (3), surface roughness occurs as a result of prolonged etching time. The full- or over-curing seems to cause latent scars on the surface of resin plates. In the case of etching using PEW solution, as shown in Fig. 3, an extremely smooth surface is maintained for up to 30 min of etching time for all kinds of plates. The PEW solution is capable of erasing the scars during the process of etching, while the aqueous solution resulted in an emphasizing of scars. The relationship between the etching time and etch-pit diameter is shown in Figs. 4 and 5. Figs. 4 and 5 represent the results using the aqueous solution and the PEW solution, respectively. In both cases, the diameter increases linearly with etching time. The incline indicates etching speed. In Figs. 4 and 5, the etching speeds of under-cured plates are faster than those of full- or over-cured plates. The etching speeds of full- and over-cured plates are almost same for both etching solutions. From these facts, it seemed that the
Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175
173
Fig. 2. Growth of $ssion tracks on three kinds of DAP resin plates, etched with aqueous solution of 30% KOH at 90◦ C. Etching time: (a) 1 h; (b) 2 h; (c) 4 h; (d) 8 h.
Fig. 3. Growth of $ssion tracks on three kinds of DAP resin plates, etched with PEW solution at 60◦ C. Etching time: (a) 4 min; (b) 8 min; (c) 15 min; (d) 30 min.
over-cured plates have the same characteristics as those of full-cured plates. In the case of the perpendicular incidence of $ssion fragments to the plate, the following relationship exists among
the bulk etching rate Vb (m=h), the track etching rate Vt (m=h) and etch-pits diameter D (m). (Durrani and Bull, 1986). D = 2Vb t (Vt − Vb )=(Vt + Vb ); (1)
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Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175
4. Discussion
Fig. 4. Relationship between etching time and etch-pit diameter in the case of etching with aqueous solution of 30% KOH at 90◦ C.
It was found that the three kinds of plates had a detection e6ciency of about 100% for $ssion fragments, and were insensitive to -particles, fast and thermal neutrons. Therefore, all three can be used as $ssion tracks detectors. However, from the points of view of the etching speed and surface smoothness, under-curing seems to be desirable for polymerizing DAP resin plates. When an under-cured CR-39 resin plates was examined, it was found that a nonlinear relationship existed in etching speed, which implied that a gradient in Vb from the surface to the depth existed. In addition, an appropriate heat-treatment induced post-curing e1ects to the under-cured CR-39. (Tsuruta, 1997). In the case of the DAP resin plates there was a linear relationship as shown in Figs. 4 and 5. ◦ ◦ Following heat treatments from 160 C to 260 C lasting 1 h for the under-cured DAP resin plates, it was found that the detection e6ciency of $ssion tracks was una1ected ◦ below 240 C. In addition, post-curing e1ects were not observed. The solid-state nuclear track detector is generally insensitive to low LET radiation such as -, - and X-rays. As a result of -ray exposures from 10 kGy to 5 MGy for the under-cured DAP resin plates, the detection e6ciency was una1ected under conditions below 1 MGy (Tsuruta, 2001a). In conclusion, the under-cured DAP resin plate seems to be valuable for the detection of $ssion fragments in all environments, in which a background radiation composed of -particles, fast and thermal neutrons, and low LET radiations exists.
Acknowledgements
Fig. 5. Relationship between etching time and etch-pit diameter in the case of etching with PEW solution at 60◦ C.
where t is the etching time (h). In the case of DAP resin, Vt Vb . Accordingly, D can be expressed simply by D = 2Vb t:
(2)
From the results shown in Fig. 4 using Eq. (2), the bulk etching rates of under-, full- and over-cured plates were calculated to be 0.25, 0.15 and 0:15 m=h, respectively, for the aqueous solution. From the results shown in Fig. 5, using Eq. (2), the bulk etching rates of under-, full- and over-cured plates were calculated to be 33, 15 and 15 m=h, respectively, for the PEW solution.
The authors wish to express their appreciation to Mr. O. Murata and Mr. M. Okamoto of the Yamamoto Kogaku Co. Ltd., for their assistance in the preparation of DAP resin plates.
References Durrani, S.A., Bull, R.K., 1986. Solid State Nuclear Track Detection. Pergamon Press, Oxford, p. 54. Somogyi, G., Hunyadi, I., 1979. Etching properties of the CR-39 polymeric nuclear track detector. In: FranOcois, H., Kurtz, N., Massue, J.P., Monnin, M., Schmitt, R., Durrani, S.A. (Eds.), Solid State Nuclear Track Detectors. Proceedings of the Tenth International Conference, Lyon. Pergamon Press, Oxford, pp. 443– 452. Somogyi, G., Medveczky, L., Hundadi, I., Nyako, B., 1977. Automatic spark counting of alpha-tracks in plastic foils. Nucl. Track Detect. 1, 131–138.
Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175 Tsuruta, T., 1997. E1ects of heat-treatment gamma-ray irradiation on the etch-pit formation in allyl diglycol carbonate resin. J. Nucl. Sci. Technol. 34, 1015–1021. Tsuruta, T., 1999. Characteristics of diallyl phthalate resin as a $ssion track detector. Radiat. Meas. 31, 99–102. Tsuruta, T., 2000. Diallyl phthalate resin and its copolymers counting allyl diglycol carbonate as nuclear track detector. Radiat. Meas. 32, 289–297.
175
Tsuruta, T., 2001a. Neutron dosimetry using diallyl phthalate resin. Reactor dosimetry, Radiation metrology and Assessment. ASTM STP-1398, 789 –796. Tsuruta, T., 2001b. Reduction in etching time for $ssion tracks in diallyl phthalate resin. Radiat. Meas. 34, 167–170.
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Polymerizing condition of DAP resin as $ssion track detector Y. Koguchi ∗ , T. Tsuruta Atomic Energy Research Institute, Kinki University, Kowakae, Higashi-Osaka, 577-8502, Japan Received 31 October 2001; received in revised form 14 December 2001; accepted 22 January 2002
Abstract Three kinds of diallyl phthalate resin plates were cast under di1erent polymerizing conditions. The plates were irradiated with $ssion fragments, -particles, fast and thermal neutrons. After irradiation, the plates were etched with an aqueous solution or a PEW solution. After etching, enlarged nuclear tracks on the plates were observed and counted using an optical microscope. All plates were found to have high detection e6ciency for $ssion fragments, but to be insensitive to -particles, fast and thermal neutrons. The etching speed of $ssion tracks on under-cured plates was faster than that on full- and over-cured plates whichever etching solution was used. In the case of adopting the aqueous solution, surface roughness occurs remarkably on the full- and over-cured plates in comparison with the under-cured plates. From these experimental results the conclusion was c 2002 Elsevier drawn that the under-cured plate was superior to the full- and over-cured plates as $ssion track detector. Science Ltd. All rights reserved. Keywords: Polymerization condition; DAP resin; Diallyl phthalate; Nuclear track detector; Fission fragment; -particle; Fast and thermal neutrons; PEW solution; Under-, full- or over-curing
1. Introduction Diallyl phthalate (DAP) resin is a thermosetting plastic. The resin is widely used as parts in electrical devices, precision apparatus, aircraft and building materials, since it is excellent with regard to heat, chemical and insulating resistance, and dimensional stability. In addition, the resin is used as spectacle lenses because of its high refractive index and appropriate hardness. The ortho-type DAP resin plate has a detection e6ciency of about 100% for $ssion fragments of both perpendicular and random incidence. However, the plate is insensitive to -particles and fast neutrons. (Tsuruta, 1999). This property is suitable for detecting selected $ssion fragments, which sometimes coexist with -particles or fast neutrons. In the case of the etching with aqueous solution of KOH, an etching time of 2– 4 hours (h) is required in order to obtain etch-pits of appropriate size for counting. In order to reduce the etching time, we tried PEW solution containing
∗
Corresponding author. Fax: +81-6-6721-3743. E-mail address: [email protected] (Y. Koguchi).
KOH, ethanol and water. The PEW solution had been used for the etching of polycarbonate (Somogyi et al., 1977) and CR-39 resin (Somogyi and Hunyadi, 1979). It was found that PEW solution made the etching time for DAP resin less than one-tenth of the etching time using aqueous solution (Tsuruta, 2001b). It is the purpose of this study to $nd suitable polymerizing conditions in order to obtain the DAP resin plates possessing a suitable etching time and smooth surface after etching for use in nuclear track detection.
2. Materials and methods 2.1. Casting of the plates The main constituent of the plates was the ortho-type DAP. The diisopropyl peroxy dicarbonate (IPP) was added at a concentration of 3% as a polymerizing initiator. The DAP solution mixed with IPP was poured into sandwich moulds, which was made up of two parallel Hat glasses and an elasticated gasket. The moulds containing the mixture were placed in an electric oven and treated with three kinds
c 2002 Elsevier Science Ltd. All rights reserved. 1350-4487/02/$ - see front matter PII: S 1 3 5 0 - 4 4 8 7 ( 0 2 ) 0 0 0 4 4 - 6
172
Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175
of UTR-KINKI. The thermal neutron Huence was obtained by measuring the activity of irradiated Au foils. 2.4. Etching and observation of etch-pits After irradiation, one group of the plates was etched in ◦ an aqueous solution of 30% KOH at 90 C. The etching time was from 30 min to 16 h. Another group of plates was etched in a PEW solution, which consisted of 15% KOH, ◦ 65% ethanol and 20% water, and was maintained at 60 C. The etching time was from 4 to 60 min. The solution was agitated by magnetic-driven vanes during etching. After etching, the plates were immediately washed clean in cold Howing tap water and dried under clean ventilation. The shape of the etch-pits was observed, and the number of the etch-pits was counted using an optical microscope. Fig. 1. Three kinds of thermal histories for polymerization of DAP resin plates.
of heat histories as shown in Fig. 1. When the temperature ◦ ◦ dropped to 50 C or 70 C, the newly formed plates were removed from the moulds. The periods of heat treatment for curing were about 27, 49 or 74 h. The 49 h curing was considered to be a standard condition for full polymerization in the manufacturing process of spectacle lenses. Therefore, we named the 27, 49 and 74 h curing plates, respectively, under-, full- and over-cured plates. Three kinds of colorless, transparent plates were formed which were 550 mm ×550 mm and 1:6 mm thick. All plates were able to be cut easily with a plastic cutter. The rectangular plates of about 30 mm × 10 mm were used for the following experiments. 2.2. Irradiation of 2ssion fragments and -particles The $rst set of the plates were arranged horizontally parallel to an electro-deposited plane standard source of Cf-252. The density of incident particles was calculated from the disintegration rate and radius of the source, the distance between the source and the plate and the irradiation time. The distance was set at pre-selected 1 cm. Fission fragments and -particles were slowed down by air, and hit the surface almost perpendicularly, because the radius of the source is small (Tsuruta, 2000). 2.3. Irradiation of fast and thermal neutrons The second set of the plates was irradiated with fast neutrons from a Pu–Be source, which was utilized to obtain several MeV neutrons. The fast neutron Huence was calculated from the source intensity, distance between the source and the plate, and the irradiation time. The third set of the plates was irradiated with thermal neutrons from a reactor
3. Experimental results Figs. 2 and 3 reveal the transition in the shape of etch-pits on the three kinds of plates which were irradiated with $ssion fragments and -particles. The plates of Figs. 2 and 3 were etched using the aqueous solution and the PEW solution, respectively. In Figs. 2 and 3, a series of photographs arranged lengthwise represents the transition of the same area of a plate at successive stages of etching. From a comparison between the density of the etch-pits and the density of incident particles, we recognized that the etch-pits which appeared were caused by the $ssion fragments. The detection e6ciency of the $ssion fragments was almost 100%. The etch-pits caused by -particle, fast and thermal neutron irradiation could not be found for the three kinds of plates under the above-mentioned etching conditions. In the case of Fig. 2(1), a relatively smooth surface is maintained for up to 8 h of etching time. However, in the case of Figs. 2(2) and (3), surface roughness occurs as a result of prolonged etching time. The full- or over-curing seems to cause latent scars on the surface of resin plates. In the case of etching using PEW solution, as shown in Fig. 3, an extremely smooth surface is maintained for up to 30 min of etching time for all kinds of plates. The PEW solution is capable of erasing the scars during the process of etching, while the aqueous solution resulted in an emphasizing of scars. The relationship between the etching time and etch-pit diameter is shown in Figs. 4 and 5. Figs. 4 and 5 represent the results using the aqueous solution and the PEW solution, respectively. In both cases, the diameter increases linearly with etching time. The incline indicates etching speed. In Figs. 4 and 5, the etching speeds of under-cured plates are faster than those of full- or over-cured plates. The etching speeds of full- and over-cured plates are almost same for both etching solutions. From these facts, it seemed that the
Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175
173
Fig. 2. Growth of $ssion tracks on three kinds of DAP resin plates, etched with aqueous solution of 30% KOH at 90◦ C. Etching time: (a) 1 h; (b) 2 h; (c) 4 h; (d) 8 h.
Fig. 3. Growth of $ssion tracks on three kinds of DAP resin plates, etched with PEW solution at 60◦ C. Etching time: (a) 4 min; (b) 8 min; (c) 15 min; (d) 30 min.
over-cured plates have the same characteristics as those of full-cured plates. In the case of the perpendicular incidence of $ssion fragments to the plate, the following relationship exists among
the bulk etching rate Vb (m=h), the track etching rate Vt (m=h) and etch-pits diameter D (m). (Durrani and Bull, 1986). D = 2Vb t (Vt − Vb )=(Vt + Vb ); (1)
174
Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175
4. Discussion
Fig. 4. Relationship between etching time and etch-pit diameter in the case of etching with aqueous solution of 30% KOH at 90◦ C.
It was found that the three kinds of plates had a detection e6ciency of about 100% for $ssion fragments, and were insensitive to -particles, fast and thermal neutrons. Therefore, all three can be used as $ssion tracks detectors. However, from the points of view of the etching speed and surface smoothness, under-curing seems to be desirable for polymerizing DAP resin plates. When an under-cured CR-39 resin plates was examined, it was found that a nonlinear relationship existed in etching speed, which implied that a gradient in Vb from the surface to the depth existed. In addition, an appropriate heat-treatment induced post-curing e1ects to the under-cured CR-39. (Tsuruta, 1997). In the case of the DAP resin plates there was a linear relationship as shown in Figs. 4 and 5. ◦ ◦ Following heat treatments from 160 C to 260 C lasting 1 h for the under-cured DAP resin plates, it was found that the detection e6ciency of $ssion tracks was una1ected ◦ below 240 C. In addition, post-curing e1ects were not observed. The solid-state nuclear track detector is generally insensitive to low LET radiation such as -, - and X-rays. As a result of -ray exposures from 10 kGy to 5 MGy for the under-cured DAP resin plates, the detection e6ciency was una1ected under conditions below 1 MGy (Tsuruta, 2001a). In conclusion, the under-cured DAP resin plate seems to be valuable for the detection of $ssion fragments in all environments, in which a background radiation composed of -particles, fast and thermal neutrons, and low LET radiations exists.
Acknowledgements
Fig. 5. Relationship between etching time and etch-pit diameter in the case of etching with PEW solution at 60◦ C.
where t is the etching time (h). In the case of DAP resin, Vt Vb . Accordingly, D can be expressed simply by D = 2Vb t:
(2)
From the results shown in Fig. 4 using Eq. (2), the bulk etching rates of under-, full- and over-cured plates were calculated to be 0.25, 0.15 and 0:15 m=h, respectively, for the aqueous solution. From the results shown in Fig. 5, using Eq. (2), the bulk etching rates of under-, full- and over-cured plates were calculated to be 33, 15 and 15 m=h, respectively, for the PEW solution.
The authors wish to express their appreciation to Mr. O. Murata and Mr. M. Okamoto of the Yamamoto Kogaku Co. Ltd., for their assistance in the preparation of DAP resin plates.
References Durrani, S.A., Bull, R.K., 1986. Solid State Nuclear Track Detection. Pergamon Press, Oxford, p. 54. Somogyi, G., Hunyadi, I., 1979. Etching properties of the CR-39 polymeric nuclear track detector. In: FranOcois, H., Kurtz, N., Massue, J.P., Monnin, M., Schmitt, R., Durrani, S.A. (Eds.), Solid State Nuclear Track Detectors. Proceedings of the Tenth International Conference, Lyon. Pergamon Press, Oxford, pp. 443– 452. Somogyi, G., Medveczky, L., Hundadi, I., Nyako, B., 1977. Automatic spark counting of alpha-tracks in plastic foils. Nucl. Track Detect. 1, 131–138.
Y. Koguchi, T. Tsuruta / Radiation Measurements 35 (2002) 171 – 175 Tsuruta, T., 1997. E1ects of heat-treatment gamma-ray irradiation on the etch-pit formation in allyl diglycol carbonate resin. J. Nucl. Sci. Technol. 34, 1015–1021. Tsuruta, T., 1999. Characteristics of diallyl phthalate resin as a $ssion track detector. Radiat. Meas. 31, 99–102. Tsuruta, T., 2000. Diallyl phthalate resin and its copolymers counting allyl diglycol carbonate as nuclear track detector. Radiat. Meas. 32, 289–297.
175
Tsuruta, T., 2001a. Neutron dosimetry using diallyl phthalate resin. Reactor dosimetry, Radiation metrology and Assessment. ASTM STP-1398, 789 –796. Tsuruta, T., 2001b. Reduction in etching time for $ssion tracks in diallyl phthalate resin. Radiat. Meas. 34, 167–170.