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Registration temperature effect on sensitivity of CR-39(DOP) and SR-90 polymer track detectors
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Radiation Measurements 36 (2003) 89 – 92 www.elsevier.com/locate/radmeas
Registration temperature e ect on sensitivity of CR-39(DOP) and SR-90 polymer track detectors P.K. Diwana , Vishal Sharmaa , S.K. Sharmab , Shyam Kumara;∗ a Department
b Department
of Physics, Kurukshetra University, Kurukshetra - 136 119, India of Applied Physics, Regional Engineering College, Kurukshetra - 136 119, India Received 21 October 2002; accepted 22 April 2003
Abstract The samples of CR-39(DOP) and SR-90 polymer track detectors have been exposed to -particles from 241 Am source in an exposure unit. The temperature of the detectors during irradiation has been varied from ∼ − 30◦ C to 70◦ C. These exposed samples have been etched in 6:25 N NaOH solution at 60◦ C for various etching times. The variation of sensitivity of these detectors as a function of registration temperature has been studied. It has been observed that at the 9xed registration temperature, the sensitivity of SR-90 is more than CR-39(DOP) polymer track detector. However, the enhancement in sensitivity with the decrease in registration temperature is more pronounced in case of CR-39(DOP) than SR-90. c 2003 Elsevier Ltd. All rights reserved. Keywords: CR-39(DOP); SR-90; Sensitivity; Etching; Registration temperature
1. Introduction CR-39, the versatile nuclear track detector of unique promise, since its recognition as a track detector in 1978 (Cartwright et al., 1978), has grown in age and reputation over more than two decades. Owing to excellent recording, etching and optical properties, it has found invaluable and indispensable use in most of the SSNTD applications. It would be no exaggeration to mention that CR-39 has given an impetus and a new direction to SSNTD research. As a material, CR-39 is a highly cross-linked thermoset polymer prepared by the polymerization of liquid monomer— diethylene glycol bis(allyl carbonate) (Stejny, 1987). Some of the drawbacks of CR-39 like the formation of opaque layer on its surface after prolonged etching and variation in sensitivity with depth and with surface positions were overcome by adding 1% dioctylphythalate to CR-39 monomer and the improved polymer is known as CR-39(DOP) (Tarle et al., 1981). In order to develop polymers with still better ∗ Corresponding author. Tel.: +91-1744-38410; fax: +91-1744-38277. E-mail addresses: [email protected], [email protected] (S. Kumar).
sensitivity, Fujii et al. (1993) produced a new polymeric track detector named SR-90 containing oligo diethylene glycol carbonate linkages. The molecular structure of SR-90 and CR-39 is very similar except that the average length of carbonate linkages in SR-90 is about 1.6 times than in CR-39 (Fujii et al., 1993, 1997). It is well documented that the sensitivities of polymeric track detectors are a ected with environmental conditions before, during and after the exposure (Durrani, 1991; Heins and Enge, 1986; Karamdoust and Durrani, 1991; Kumar et al., 1986; O’Sullivan and Thompson, 1981; Portwood et al., 1986). The e ect of vacuum, oxygen and carbon dioxide on the track registration in SR-90 has already been reported (Fujii et al., 1995, 1997). In the present work, we have studied the e ect of registration temperature on the track registration sensitivities of CR-39(DOP) and SR-90 polymeric track detectors, exposed to 5:45 MeV alpha particles, maintaining the detectors at various temperatures (∼−30◦ C to +70◦ C) during irradiation. 2. Exposure setup The detector samples have been irradiated in an exposure unit (Fig. 1) in our laboratory. Exposure unit contains three
c 2003 Elsevier Ltd. All rights reserved. 1350-4487/03/$ - see front matter doi:10.1016/S1350-4487(03)00100-8
90
P.K. Diwan et al. / Radiation Measurements 36 (2003) 89 – 92
Fig. 1. Exposure setup.
uprights, which are used for mounting the detector samples and for holding the source and the collimator. The source and the collimator uprights can be moved horizontally so as to adjust their distance from the detector sample. Provision for vertical and rotational motion of this source upright has also been made for the purpose of alignment of source with collimator and detector. The following are the various features of the exposure unit: • We have used the 241 Am electrodeposited alpha source on 25 mm dia × 0:5 mm thick stainless steel planchette with active diameter of 10 mm and strength 0:49 Ci. • A collimator of brass containing a large number of closely packed holes is employed for the exposure of detector to a collimated beam of particles.
• A rectangular aluminium foil (∼5 mm thick) can be inserted between the source and the collimator uprights so as to stop irradiation whenever desired. Its operation is guided mechanically from outside. • The detector sample is tightly held on a copper block, which is placed on a hollow copper box. • Source, collimator, aluminum guard foil and detector are inside a glass chamber. Using a suitable vacuum pump, the system can be evacuated to desired pressure, which is measured with the help of a gauge. • It is possible to vary the temperature at which the detector is exposed. Using a cryostat, a suitable liquid can be maintained at any 9xed temperature in the range ∼ − 30◦ C to +90◦ C. There is an arrangement for constant Iow of the liquid through the hollow
P.K. Diwan et al. / Radiation Measurements 36 (2003) 89 – 92
91
copper box on which the block holding the sample is placed. • In order to measure the temperature of the detector sample directly during exposure, we have assembled a digital temperature indicator using PT-100 sensor. 3. Experimental details The samples of both CR-39(DOP) and SR-90 have been exposed simultaneously in vacuum (∼10−2 Torr) to collimated beams of 5:45 MeV alpha particles from 241 Am source, at normal incidence. The temperature of the di erent sets of the detectors during irradiation has been varied from ∼ − 30◦ C to +70◦ C. The exposed samples of CR-39(DOP) and SR-90 have been etched simultaneously in 6:25 N NaOH solution at 60◦ C for di erent etching times. The track diameter has been measured using the transmitted light Leitz Dialux-20 microscope attached with eyepiece screw micrometer. All measurement have been made at a total magni9cation of 900× with a least count of 0:23 m. The standard deviation in the diameter measurements has been found to be within 5%. The bulk etch rate has been measured using thickness measurement technique. The sensitivity of the detector, which is de9ned as the ratio of track etch rate (vt ) to bulk etch rate (vb ), has been determined using the relation (Durrani and Bull, 1987): vt 4v2 t 2 + D2 S= = 2b 2 vb 4vb t − D2
Fig. 2. Variation of track diameter (m) with registration temperature (◦ C) for -particles in CR-39(DOP) for di erent etching time.
where D is the track diameter and t is the etching time. 4. Results and discussion Fig. 2 presents the variation of track diameter as a function of the temperature of detector during irradiation (Registration temperature) for CR-39(DOP) polymer track detector, exposed to 5:45 MeV alpha particles, for various etching times. Fig. 3 shows similar variation for SR-90 polymer track detector. From Figs. 2 and 3, it is clear that there is an increase in the track diameter with decreasing registration temperature of the detector. However, the bulk etch rate of both the detectors has been found to be remain essentially constant in the entire temperature range. Such an increase in the track diameter at lower temperature shows an enhancement in the track etch rate with decreasing registration temperature. Thus, there is a clear-cut enhancement in the sensitivity of the detectors with decreasing registration temperature, which is clearly depicted in Fig. 4. A probable cause for the decrease in the sensitivity with increase in registration temperature may be partially attributed to the e ect of instant healing of the developing damage. The damage in polymers as a result of passage of ionizing radiation leads to the formation of free redicals.
Fig. 3. Variation of track diameter (m) with registration temperature (◦ C) for -particles in SR-90 for di erent etching time.
The enhanced temperature during irradiation leads to the increased mobility of the free redicals resulting in greater probability of their recombinations and hence the extent of damage is a little reduced which possibly give rise to the observed decrease in the sensitivity. Fig. 5 presents the normalized sensitivity (with respect to the sensitivity at room temperature) as a function of registration temperature for CR-39(DOP) and SR-90 polymer track detectors. It is clear from the 9gure that the e ect of
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P.K. Diwan et al. / Radiation Measurements 36 (2003) 89 – 92
ture e ect is more pronounced in CR-39(DOP) in comparison to SR-90. The correlation of sensitivity as a function of registration temperature with the physical properties of detector material like dielectric constant, etc. currently under progress in order to evolve a quantitative description. Acknowledgements The authors are thankful to Dr. M. Fujii, Aomori University, 2-3-1 Kobata, Aomori, Japan and Dr. R.H. Iyer, Nuclear Recycle Group, Bhabha Atomic Research Centre, Trombay, Mumbai, India for material support. One of the authors (P.K. Diwan) is thankful to the Council of Scienti9c and Industrial Research (CSIR), New Delhi, India, for providing 9nancial assistance by way of Senior Research Fellowship.
Fig. 4. Variation of sensitivity of CR-39(DOP) and SR-90 with registration temperature (◦ C).
Fig. 5. Variation of normalized sensitivity of CR-39(DOP) and SR-90 with registration temperature (◦ C).
registration temperature on CR-39(DOP) seems to be slightly more pronounced than in SR-90. 5. Conclusion It may be concluded that at 9xed registration temperature, the sensitivity of the SR-90 detector is more as compared to CR-39(DOP) detector. However, the registration tempera-
References Cartwright, B.G., Shirk, E.K., Price, P.B., 1978. A nuclear track recording polymer of unique sensitivity and resolution. Nucl. Instrum. Methods 153, 457–460. Durrani, S.A., 1991. The e ect of irradiation temperature on the response of track recording crystalline and polymeric media: brief review. Nucl. Tracks Radiat. Meas. 19 (1– 4), 61–70. Durrani, S.A., Bull, R.K., 1987. Solid State Nuclear Track Detection: Principles, Methods and Applications. Pergamon Press, Oxford. Fujii, M., Asari, T., Yokota, R., Kobayashi, T., Hasegawa, H., 1993. Aging e ects on a new polymeric track detector SR-90 and a model of the nuclear track formation. Nucl. Track Radiat. Meas. 22 (1– 4), 199–204. Fujii, M., Yokota, R., Kobayashi, T., Hasegawa, H., 1995. Sensitization of polymeric track detectors with carbon dioxide. Radiat. Meas. 25 (1– 4), 141–144. Fujii, M., Yokota, R., Kobayashi, T., Hasegawa, H., 1997. E ect of vacuum, oxygen and carbon dioxide on the track registration in SR-90 and CR-39. Radiat. Meas. 28 (1– 6), 61–64. Heins, T., Enge, W., 1986. Oxygen e ect on the etch rate in CR-39 plastic detector. Nucl. Tracks 12, 87–89. Karamdoust, N.A., Durrani, S.A., 1991. E ect of registration temperature on the response of CR-39 to alpha particles and 9ssion fragments. Nucl.Tracks Radiat. Meas. 19 (1– 4), 179–184. Kumar, S., Chander, S., Yadav, J.S., Sharma, A.P., 1986. Some environmental e ect studies on the response of CR-39(DOP) plastic track detector. Nucl. Tracks 12 (1– 6), 129–132. O’Sullivan, D., Thompson, A., 1981. The observation of a sensitivity dependence on temperature during registration in solid state nuclear track detectors. Nucl. Tracks 4, 271–276. Portwood, T., Henshaw, D.L., Stejny, J., 1986. Aging e ect in CR-39. Nucl. Tracks 12, 109–112. Stejny, J., 1987. The polymer physics on CR-39—the state of understanding. Radiat. Prot. Dosim. 20, 31–36. Tarle, G., Ahlen, S.P., Price, P.B., 1981. Energy straggling eliminated as a limitation to charge resolution of transmission detectors. Nature 293, 556–558.
Radiation Measurements 36 (2003) 89 – 92 www.elsevier.com/locate/radmeas
Registration temperature e ect on sensitivity of CR-39(DOP) and SR-90 polymer track detectors P.K. Diwana , Vishal Sharmaa , S.K. Sharmab , Shyam Kumara;∗ a Department
b Department
of Physics, Kurukshetra University, Kurukshetra - 136 119, India of Applied Physics, Regional Engineering College, Kurukshetra - 136 119, India Received 21 October 2002; accepted 22 April 2003
Abstract The samples of CR-39(DOP) and SR-90 polymer track detectors have been exposed to -particles from 241 Am source in an exposure unit. The temperature of the detectors during irradiation has been varied from ∼ − 30◦ C to 70◦ C. These exposed samples have been etched in 6:25 N NaOH solution at 60◦ C for various etching times. The variation of sensitivity of these detectors as a function of registration temperature has been studied. It has been observed that at the 9xed registration temperature, the sensitivity of SR-90 is more than CR-39(DOP) polymer track detector. However, the enhancement in sensitivity with the decrease in registration temperature is more pronounced in case of CR-39(DOP) than SR-90. c 2003 Elsevier Ltd. All rights reserved. Keywords: CR-39(DOP); SR-90; Sensitivity; Etching; Registration temperature
1. Introduction CR-39, the versatile nuclear track detector of unique promise, since its recognition as a track detector in 1978 (Cartwright et al., 1978), has grown in age and reputation over more than two decades. Owing to excellent recording, etching and optical properties, it has found invaluable and indispensable use in most of the SSNTD applications. It would be no exaggeration to mention that CR-39 has given an impetus and a new direction to SSNTD research. As a material, CR-39 is a highly cross-linked thermoset polymer prepared by the polymerization of liquid monomer— diethylene glycol bis(allyl carbonate) (Stejny, 1987). Some of the drawbacks of CR-39 like the formation of opaque layer on its surface after prolonged etching and variation in sensitivity with depth and with surface positions were overcome by adding 1% dioctylphythalate to CR-39 monomer and the improved polymer is known as CR-39(DOP) (Tarle et al., 1981). In order to develop polymers with still better ∗ Corresponding author. Tel.: +91-1744-38410; fax: +91-1744-38277. E-mail addresses: [email protected], [email protected] (S. Kumar).
sensitivity, Fujii et al. (1993) produced a new polymeric track detector named SR-90 containing oligo diethylene glycol carbonate linkages. The molecular structure of SR-90 and CR-39 is very similar except that the average length of carbonate linkages in SR-90 is about 1.6 times than in CR-39 (Fujii et al., 1993, 1997). It is well documented that the sensitivities of polymeric track detectors are a ected with environmental conditions before, during and after the exposure (Durrani, 1991; Heins and Enge, 1986; Karamdoust and Durrani, 1991; Kumar et al., 1986; O’Sullivan and Thompson, 1981; Portwood et al., 1986). The e ect of vacuum, oxygen and carbon dioxide on the track registration in SR-90 has already been reported (Fujii et al., 1995, 1997). In the present work, we have studied the e ect of registration temperature on the track registration sensitivities of CR-39(DOP) and SR-90 polymeric track detectors, exposed to 5:45 MeV alpha particles, maintaining the detectors at various temperatures (∼−30◦ C to +70◦ C) during irradiation. 2. Exposure setup The detector samples have been irradiated in an exposure unit (Fig. 1) in our laboratory. Exposure unit contains three
c 2003 Elsevier Ltd. All rights reserved. 1350-4487/03/$ - see front matter doi:10.1016/S1350-4487(03)00100-8
90
P.K. Diwan et al. / Radiation Measurements 36 (2003) 89 – 92
Fig. 1. Exposure setup.
uprights, which are used for mounting the detector samples and for holding the source and the collimator. The source and the collimator uprights can be moved horizontally so as to adjust their distance from the detector sample. Provision for vertical and rotational motion of this source upright has also been made for the purpose of alignment of source with collimator and detector. The following are the various features of the exposure unit: • We have used the 241 Am electrodeposited alpha source on 25 mm dia × 0:5 mm thick stainless steel planchette with active diameter of 10 mm and strength 0:49 Ci. • A collimator of brass containing a large number of closely packed holes is employed for the exposure of detector to a collimated beam of particles.
• A rectangular aluminium foil (∼5 mm thick) can be inserted between the source and the collimator uprights so as to stop irradiation whenever desired. Its operation is guided mechanically from outside. • The detector sample is tightly held on a copper block, which is placed on a hollow copper box. • Source, collimator, aluminum guard foil and detector are inside a glass chamber. Using a suitable vacuum pump, the system can be evacuated to desired pressure, which is measured with the help of a gauge. • It is possible to vary the temperature at which the detector is exposed. Using a cryostat, a suitable liquid can be maintained at any 9xed temperature in the range ∼ − 30◦ C to +90◦ C. There is an arrangement for constant Iow of the liquid through the hollow
P.K. Diwan et al. / Radiation Measurements 36 (2003) 89 – 92
91
copper box on which the block holding the sample is placed. • In order to measure the temperature of the detector sample directly during exposure, we have assembled a digital temperature indicator using PT-100 sensor. 3. Experimental details The samples of both CR-39(DOP) and SR-90 have been exposed simultaneously in vacuum (∼10−2 Torr) to collimated beams of 5:45 MeV alpha particles from 241 Am source, at normal incidence. The temperature of the di erent sets of the detectors during irradiation has been varied from ∼ − 30◦ C to +70◦ C. The exposed samples of CR-39(DOP) and SR-90 have been etched simultaneously in 6:25 N NaOH solution at 60◦ C for di erent etching times. The track diameter has been measured using the transmitted light Leitz Dialux-20 microscope attached with eyepiece screw micrometer. All measurement have been made at a total magni9cation of 900× with a least count of 0:23 m. The standard deviation in the diameter measurements has been found to be within 5%. The bulk etch rate has been measured using thickness measurement technique. The sensitivity of the detector, which is de9ned as the ratio of track etch rate (vt ) to bulk etch rate (vb ), has been determined using the relation (Durrani and Bull, 1987): vt 4v2 t 2 + D2 S= = 2b 2 vb 4vb t − D2
Fig. 2. Variation of track diameter (m) with registration temperature (◦ C) for -particles in CR-39(DOP) for di erent etching time.
where D is the track diameter and t is the etching time. 4. Results and discussion Fig. 2 presents the variation of track diameter as a function of the temperature of detector during irradiation (Registration temperature) for CR-39(DOP) polymer track detector, exposed to 5:45 MeV alpha particles, for various etching times. Fig. 3 shows similar variation for SR-90 polymer track detector. From Figs. 2 and 3, it is clear that there is an increase in the track diameter with decreasing registration temperature of the detector. However, the bulk etch rate of both the detectors has been found to be remain essentially constant in the entire temperature range. Such an increase in the track diameter at lower temperature shows an enhancement in the track etch rate with decreasing registration temperature. Thus, there is a clear-cut enhancement in the sensitivity of the detectors with decreasing registration temperature, which is clearly depicted in Fig. 4. A probable cause for the decrease in the sensitivity with increase in registration temperature may be partially attributed to the e ect of instant healing of the developing damage. The damage in polymers as a result of passage of ionizing radiation leads to the formation of free redicals.
Fig. 3. Variation of track diameter (m) with registration temperature (◦ C) for -particles in SR-90 for di erent etching time.
The enhanced temperature during irradiation leads to the increased mobility of the free redicals resulting in greater probability of their recombinations and hence the extent of damage is a little reduced which possibly give rise to the observed decrease in the sensitivity. Fig. 5 presents the normalized sensitivity (with respect to the sensitivity at room temperature) as a function of registration temperature for CR-39(DOP) and SR-90 polymer track detectors. It is clear from the 9gure that the e ect of
92
P.K. Diwan et al. / Radiation Measurements 36 (2003) 89 – 92
ture e ect is more pronounced in CR-39(DOP) in comparison to SR-90. The correlation of sensitivity as a function of registration temperature with the physical properties of detector material like dielectric constant, etc. currently under progress in order to evolve a quantitative description. Acknowledgements The authors are thankful to Dr. M. Fujii, Aomori University, 2-3-1 Kobata, Aomori, Japan and Dr. R.H. Iyer, Nuclear Recycle Group, Bhabha Atomic Research Centre, Trombay, Mumbai, India for material support. One of the authors (P.K. Diwan) is thankful to the Council of Scienti9c and Industrial Research (CSIR), New Delhi, India, for providing 9nancial assistance by way of Senior Research Fellowship.
Fig. 4. Variation of sensitivity of CR-39(DOP) and SR-90 with registration temperature (◦ C).
Fig. 5. Variation of normalized sensitivity of CR-39(DOP) and SR-90 with registration temperature (◦ C).
registration temperature on CR-39(DOP) seems to be slightly more pronounced than in SR-90. 5. Conclusion It may be concluded that at 9xed registration temperature, the sensitivity of the SR-90 detector is more as compared to CR-39(DOP) detector. However, the registration tempera-
References Cartwright, B.G., Shirk, E.K., Price, P.B., 1978. A nuclear track recording polymer of unique sensitivity and resolution. Nucl. Instrum. Methods 153, 457–460. Durrani, S.A., 1991. The e ect of irradiation temperature on the response of track recording crystalline and polymeric media: brief review. Nucl. Tracks Radiat. Meas. 19 (1– 4), 61–70. Durrani, S.A., Bull, R.K., 1987. Solid State Nuclear Track Detection: Principles, Methods and Applications. Pergamon Press, Oxford. Fujii, M., Asari, T., Yokota, R., Kobayashi, T., Hasegawa, H., 1993. Aging e ects on a new polymeric track detector SR-90 and a model of the nuclear track formation. Nucl. Track Radiat. Meas. 22 (1– 4), 199–204. Fujii, M., Yokota, R., Kobayashi, T., Hasegawa, H., 1995. Sensitization of polymeric track detectors with carbon dioxide. Radiat. Meas. 25 (1– 4), 141–144. Fujii, M., Yokota, R., Kobayashi, T., Hasegawa, H., 1997. E ect of vacuum, oxygen and carbon dioxide on the track registration in SR-90 and CR-39. Radiat. Meas. 28 (1– 6), 61–64. Heins, T., Enge, W., 1986. Oxygen e ect on the etch rate in CR-39 plastic detector. Nucl. Tracks 12, 87–89. Karamdoust, N.A., Durrani, S.A., 1991. E ect of registration temperature on the response of CR-39 to alpha particles and 9ssion fragments. Nucl.Tracks Radiat. Meas. 19 (1– 4), 179–184. Kumar, S., Chander, S., Yadav, J.S., Sharma, A.P., 1986. Some environmental e ect studies on the response of CR-39(DOP) plastic track detector. Nucl. Tracks 12 (1– 6), 129–132. O’Sullivan, D., Thompson, A., 1981. The observation of a sensitivity dependence on temperature during registration in solid state nuclear track detectors. Nucl. Tracks 4, 271–276. Portwood, T., Henshaw, D.L., Stejny, J., 1986. Aging e ect in CR-39. Nucl. Tracks 12, 109–112. Stejny, J., 1987. The polymer physics on CR-39—the state of understanding. Radiat. Prot. Dosim. 20, 31–36. Tarle, G., Ahlen, S.P., Price, P.B., 1981. Energy straggling eliminated as a limitation to charge resolution of transmission detectors. Nature 293, 556–558.