- Email: [email protected]
Application of polystyrene films for indoor radon dosimetry as SSNTD
Applied Radiation and Isotopes 74 (2013) 23–25
Contents lists available at SciVerse ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Application of polystyrene films for indoor radon dosimetry as SSNTD Kamal Hadad a,n, Samira Sarshough a, Reza Faghihi a, Mehran Taheri b a b
Department of Nuclear Engineering, Shiraz University, Shiraz, Iran National Radiation Protection Department, Tehran, Iran
H I G H L I G H T S c c c
Presenting a new passive film detector for radon and thoron indoor dosimetry with improved sensitivity. Improving and optimizing the compact disk thick polycarbonate radon dosimetry. Suggesting a new technique for past history of indoor radon monitoring using old MRI or X-ray medical records stored in residentials.
a r t i c l e i n f o
abstract
Article history: Received 25 June 2012 Received in revised form 11 December 2012 Accepted 14 December 2012 Available online 26 December 2012
In this study, the sensitivities and calibration factors of polystyrene (PS) to 220Rn and 222Rn have been investigated. The sensitivity of compact disks (CD/DVD) as thick polycarbonates (PC) to 220Rn and 222Rn has been also obtained by applying a new etching condition. Five different brands of X-ray radiology and MRI films with polystyrene base and four brands of CD/DVDs have been studied to assess their applicability as a passive detector for indoor radon monitoring. The comparison between the sensitivities of PS samples, CD/DVDs (as thick PC) and Lexan PC to 222Rn and 220Rn shows an improved sensitivity of PS over conventional PC currently being used as solid state nuclear track detectors (SSNTD). The sensitivity of X-ray radiology PS films to 222Rn and 220Rn was found to be 8.77 7 0.591 and 0.028 7 0.006 (cm 2 kBq 1 d 1 m3). The sensitivities of MRI PS films to Rn-222 and Rn-220 was found to be 12.2 7 1.25 and 0.360 7 0.090 (cm 2 kBq 1 d 1 m3). The CD/DVD PC found to have a sensitivity of 0.178 7 0.013 and 0.0024 70.00013 (cm 2 kBq 1 d 1 m3) to 222Rn and 220Rn respectively. & 2012 Elsevier Ltd. All rights reserved.
Keywords: SSNTD Radon dosimetry Passive monitoring Polystyrene films Lexan polycarbonate
1. Introduction In the natural environment, the largest part of radiation dose received by the general public is due to the radon and its progeny (NCRP, 1987). Today, according to the UNSCEAR 1993 the concentrations of radon and its progeny in enclosed spaces may result in significant biological hazards and after smoking it is the most important cause of lung cancer (WHO, 2009). Several passive and active methods have been developed to monitor radon and its daughters (Urban and Piesch, 1981; Nikolaev et al., 1998; Hadler and Paulo, 1994). The choice of particular technique depends on the objective of the study. One of the most important and practical methods for long-time measurements of radon and its progeny in various environmental studies is the use of solid-state nuclear track detectors (Fleischer et al., 1984; Rannou et al., 1986; Sohrabi and Sadeghi, 1991; Hadler et al., 1995; Hadad et al., 2007; Hosseini Pooya et al., 2008). The science of SSNTD was born in 1958 when the first tracks were seen in a crystal of LiF by Young (1958). Fleischer et al.
n
Corresponding author. E-mail address: [email protected] (K. Hadad).
0969-8043/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2012.12.008
(1965) are the pioneers of this field who tried to introduce new applications of track detectors in different areas of science and technologies. Tommasino (1970) and Sohrabi (1974) suggested electrochemical etching method to amplification of the tracks of alpha particles and fission fragments. The track formation properties exist in many materials especially those having long molecules e.g. cellulose nitrates, polyesters or polycarbonates. On the other hand, the basic constructive materials of CD/DVDs, X-ray radiology and MRI films are polycarbonate and polystyrene, respectively. A method based on the absorption ability of some polycarbonate such as Makrofol to measure radon concentration was first employed by Pressyanov et al. (1999) and then developed and expanded by Fleischer (2002) and Tommasino et al. (2009). Radon measurements by CDs/DVDs were first proposed and explored by Pressyanov et al. (2001, 2003). Lexan PCs have been widely used for the indoor radon monitoring around the world and in Iran (Hadad and Doulatdar, 2008; Hadad et al., 2011). The use of CD/DVDs PC for 222Rn mapping has only been reported by Pressyanov (2010) who used the homestored CDs/DVDs in dwellings of three cities in Bulgaria. In this research, we used X-ray radiology and MRI films with polystyrene (PS) base and CD/DVDs with polycarbonate (PC) base for 222Rn and 220Rn dosimetry. The results of dosimetry calibration
K. Hadad et al. / Applied Radiation and Isotopes 74 (2013) 23–25
for 222Rn and 220Rn are presented and their sensitivities are compared. X-ray and MRI PS films are part of many household medical records and are usually kept for many years. Using our technique, such valuable repository of radon concentrations data in dwellings could be utilized for long term of radon monitoring studies.
2. Material and methods 2.1. Calibration sources Five different brands of X-ray radiology and MRI films with polystyrene base PS, and various brands of compact disks were chosen and cut into 2 cm 2 cm size and 2-cm diameter pieces, respectively. The PS radon dosimeters were exposed and calibrated inside a glove-box of 240 l with Uranium ore powder. Uranium ore powder contains natural Uranium which decays to radium and radon in its decay chain. The radon field was calibrated by Lucas scintillation cells calibrated in turn by using a Pylon Standard Source type RN-150 (PYLON Model TH-1025, 1989). Fig. 1 illustrates the calibration source setup (Hosseini Pooya et al., 2008). A powder of gas mantles with activity of 1.65 kBq was used as a 220Rn source. Their thorium activity was determined by gamma spectroscopy method using the 232Th standard source with determined activity (Sadagopan et al., 1997). Gamma spectrometry was carried out using a HPGe detector with a full width at half maximum (FWHM) of 1.88 keV at the 1332 keV g-ray peak of 60 Co and 0.875 keV at the 122 keV g-ray peak of 57Co. The detector was surrounded by a cylindrical heavy lead shield of 10 cm thick and internal layers of cadmium to reduce background radiation originating from building materials and cosmic rays. The HPGe detector was connected to a PC-based multi-channel analyzer for spectrometry analysis. 2.2. Electrochemical etching (ECE) process
MRI PS, X-ray PS and CD/DVD PC samples with etching intervals of 4, 3, 3 h respectively. 2.3. Counting process The images of the etched PS and PC films were obtained by a highresolution scanner (9600 dpi) with a transparency adapter (Umax Scanner Power Look). The number of tracks was counted by image processing software written in MATLAB (Hosseini Pooya et al., 2008). The sensitivities or calibration factors for 222Rn and 220Rn are calculated using the following equation (Urban and Piesch, 1981): NN 0 CF ¼ X 1 ref A 222 Rn or 220Rn, N is the total where X 1 ref is the known activity of number of tracks, N0 is the number of background tracks and A is the sample area.
3. Results and discussion The common etchant in ECE is a simple alkali and its sensitivity could be improved by adding alcohol to the aqueous solution. For the PS samples, we increased the volume ratio to increase the mobility of etchant ions and improve the etchant performance. 7000 6000
Track Density (cm-2)
24
The irradiated sheets were electrochemically etched at room temperature (25–30 1C) with different etching solutions, electric field strengths and time intervals to determine the optimum etching procedure for X-ray and MRI PS samples as well as CD/ DVD thick PCs. The etching solution ‘‘PEMEXs’’ an aqueous solution contained ethanol and 5 M KOH solution with 1:1 volume ratio for the MRI PS films, 9 M KOH solution with 1:1 volume ratio for X-ray PS films and 11 M KOH solution with 1:1 volume ratio for the compact disks. The applied high voltage (HV) was chosen to ensure an effective strength of electric field of 6, 5 and 4 kV/mm for the
5000 4000 3000
Sample 1 Sample 2 Linear Fit
2000 1000 0 0
100
200
Rn222Activity
300
400
500
(KBq-day/cm3)
Fig. 2. Calibration curve of X-ray radiology PS samples.
7000
-2
Track Density (cm )
6000
5000 4000 3000
Sample 1 Sample 2 Linear Fit
2000 1000 0 0
100
200 222
300
400 3
Rn Activity (KBq-day/cm ) Fig. 1. Radon source setup for determination of PS and PC films calibration factors.
Fig. 3. Calibration curve of MRI PS samples.
500
K. Hadad et al. / Applied Radiation and Isotopes 74 (2013) 23–25
Table 1 Results of sensitivity measurements and comparison to other studies. Study
Sensitivity to Rn222 Sensitivity to Rn220 (cm 2 kBq 1 d 1 m3) (cm 2 kBq 1 d 1 m3)
X-ray radiology PS samples 8.77 70.591 CD/DVD PC 0.360 70.090 MRI PS 12.2 71.25 Lexan PC SSNTD 8.5 70.7 (Hosseini Pooya et al., 2008) CDs/DVDs (Pressyanov, 2012; 0.463 70.062 Pressyanov et al., 2010)
0.028 70.006 0.0027 0.0001 0.178 7 0.013 0.018 70.004 0.278
We also increased the effective strength of electric field which allows starting the treeing process immediately following the application of the high voltage. Therefore, the tracks appear in shorter time than the conventional etching methods. The calibration curves of the X-ray and MRI PS samples for 222Rn are presented in Figs. 2 and 3. In both figures, the non-zero value at interception represents the track densities of the control samples due to background activity or inherent defects in PC or PS films. The sensitivities of the PS and CD/DVD PC samples to 222Rn and 220Rn are presented in Table 1. Comparing the sensitivity of our PS samples with previous studies of Lexan PCs (Hosseini Pooya et al., 2008) and CDs/DVD (Pressyanov et al., 2010, Pressyanov, 2012) we could come to the following conclusion: 1. The highest sensitivity to 222Rn and 220Rn is achievable by the MRI PS films (12.271.25 counts/cm 2 kBq 1 d 1 m3). 2. The sensitivity of the X-ray radiology PS films to 222Rn and 220 Rn is comparable with Lexan PC SSNTD (8.7770.591 compared with 8.5 70.7 counts/cm 2 kBq 1 d 1 m3). 3. The compact disks have the lowest sensitivity for 222Rn and 220 Rn. 4. Our results for CD/DVD PC samples are comparable with Pressyanov et al. (2010) results for radon; however, we have achieved faster ECE processing time intervals by optimizing the etching condition. 5. Overall, the samples have higher sensitivity to 222Rn than 220 Rn. The reason behind such phenomena is the longer half life of 222Rn compared with 220Rn. Our result points out the efficient applications of different SSNTD for radon and thoron monitoring purposes. Due to low sensitivity of CDs/DVDs, they are suitable for a high concentration of 222Rn and 220Rn or longer exposure time intervals. Due to their higher sensitivities, the MRI and X-ray PS films are suitable for low radon concentration media or shorter exposure time intervals. The stored MRI or X-ray medical records of people stored in the houses could be readily used for long-term radon and thoron exposure. However, since these records are usually
25
stored inside envelopes, the effect of such packing on radon exposure could be an important issue.
References Fleischer, R.L., Price, P.B., Walker, R.M., 1965. Solid state track detector: application to nuclear science and geophysics. Annu. Rev. Nucl. Sci. 15, 1–28. Fleischer, R.L., Turner, L.G., George, A.C., 1984. Passive measurement of working levels and effective diffusion constants of radon daughters by the nuclear track technique. Health Phys. 47, 9–19. Fleischer, R.L., 2002. Serendipitous radiation monitors. Am. Sci. 90, 324–331. Hadad, K., Doulatdar, R., Mehdizadeh, S., 2007. Indoor radon monitoring in Northern Iran using passive and active measurements. J. Environ. Radioact. 95 (1), 39–52. Hadad, K., Doulatdar, R., 2008. U-series concentration in surface and ground water resources of Ardabil province. Radiat. Protect. Dosimetry 130, 309–318. Hadad, K., Hakimdavoud, M.R., Hashemi Tilehnoee, M., 2011. Indoor radon survey in Shiraz-Iran using developed passive measurement method. Iran. J. Radiat. Res. 9, 175–182. Hadler, J.C., Paulo, S.R., 1994. Indoor radon daughter contamination monitoring: the absolute efficiency of CR-39 taking into account the plate-out effect and environmental conditions. Radiat. Protect. Dosimetry 51, 283–296. Hadler, N.J.C., Iunes, P.J., Paulo, S.R., 1995. A possibility of monitoring indoor radon daughters by using CR-39 as an alpha-spectrometer. Radiat. Meas. 25, 609–610. Hosseini Pooya, S.M., Afarideh, H., Kardan, M.R., Taheri, M., 2008. Design of an alpha spectrometry system for separated measurements of radon/thoron daughters’ concentration by Lexan PC SSNTD. Nucl. Instrum. Methods Phys. Res. 594, 44–49. National Council on Radiation and Protection and measurements, 1987. Ionizing Radiation Exposure of Population of the United States. NCRP Report No. 93. Pressyanov, D., Van Deynse, A., Buysse, J., Poffijn, A., Meesen, G., 1999. Polycarbonates: a new retrospective radon monitor. In: Proceedings of the IRPA Regional Congress on Radiation Protection, Budapest, Hungary. Pressyanov, D., Buysse, J., Van Deynse, A., Poffijn, A., Meesen, G., 2001. Indoor radon detected by compact disks. Nucl. Instrum. Methods 459, 665–666. Pressyanov, D., Buysse, J., Poffijn, A., Meesen, G., Van Deynse, A., 2003. The compact disk as radon detector—a laboratory study of the method. Health Phys. 84, 642–651. Pressyanov, D., Mitev., K., Georgiev., S., Dimitrova, I., 2010. Radon mapping by retrospective measurements—an approach based on CDs/DVDs. J. Environ. Radioact. 101, 821–825. Pressyanov, D., 2012. Retrospective measurements of thoron and radon by CDs/ DVDs: a model approach. Radiat. Protect. Dosimetry 149, 464–468. PYLON Model TH-1025, 1989. Flow Through Thoron Gas Source Instruction Manual, Pylon Electronic Development Company, Canada. Rannou, A., Jeanmaire, L., Tymen, G., Mouden, A., Naour, E., Parmentier, N., Renouard, H., 1986. Use of cellulose nitrate as radon and thoron daughters detectors for indoor measurements. Nucl. Tracks 12, 747–750. Sohrabi, M., 1974. The amplification of Recoil particle tracks in polymers and its application in fast neutron personnel dosimetry. Health Phys. 27, 598–600. Sohrabi, M., Sadeghi, M., 1991. Efficient detection and spectrometry of alphas from radon daughters in polycarbonate. Nucl. Tracks Radiat. Meas. 19, 421–422. Sadagopan, G., Nambi, K.S.V., Venkataraman, G., Sukla, V.K., Kayasth, S., 1997. Estimation of thorium in gas mantles to ascertain regulatory compliance. Radiat. Protect. Dosimetry 71, 53–56. Tommasino, L., 1970. CNCE Report RT/PRO. 71. Tommasino, L., Tommasino, M., Viola, P., 2009. Radon film-badges by solid radiators to complement track detector-based radon monitors. Radiat. Meas. 44, 719–723. Urban, M., Piesch, E., 1981. Low level environmental radon dosimetry with a passive track etch detector device. Radiat. Protect. Dosimetry 1, 97–109. World Health Organization, 2009. WHO Handbook on Indoor Radon. WHO Press, Geneva. Young, D.A., 1958. Etching of radiation damage in lithium fluoride. Nature 185, 375–377.
Contents lists available at SciVerse ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Application of polystyrene films for indoor radon dosimetry as SSNTD Kamal Hadad a,n, Samira Sarshough a, Reza Faghihi a, Mehran Taheri b a b
Department of Nuclear Engineering, Shiraz University, Shiraz, Iran National Radiation Protection Department, Tehran, Iran
H I G H L I G H T S c c c
Presenting a new passive film detector for radon and thoron indoor dosimetry with improved sensitivity. Improving and optimizing the compact disk thick polycarbonate radon dosimetry. Suggesting a new technique for past history of indoor radon monitoring using old MRI or X-ray medical records stored in residentials.
a r t i c l e i n f o
abstract
Article history: Received 25 June 2012 Received in revised form 11 December 2012 Accepted 14 December 2012 Available online 26 December 2012
In this study, the sensitivities and calibration factors of polystyrene (PS) to 220Rn and 222Rn have been investigated. The sensitivity of compact disks (CD/DVD) as thick polycarbonates (PC) to 220Rn and 222Rn has been also obtained by applying a new etching condition. Five different brands of X-ray radiology and MRI films with polystyrene base and four brands of CD/DVDs have been studied to assess their applicability as a passive detector for indoor radon monitoring. The comparison between the sensitivities of PS samples, CD/DVDs (as thick PC) and Lexan PC to 222Rn and 220Rn shows an improved sensitivity of PS over conventional PC currently being used as solid state nuclear track detectors (SSNTD). The sensitivity of X-ray radiology PS films to 222Rn and 220Rn was found to be 8.77 7 0.591 and 0.028 7 0.006 (cm 2 kBq 1 d 1 m3). The sensitivities of MRI PS films to Rn-222 and Rn-220 was found to be 12.2 7 1.25 and 0.360 7 0.090 (cm 2 kBq 1 d 1 m3). The CD/DVD PC found to have a sensitivity of 0.178 7 0.013 and 0.0024 70.00013 (cm 2 kBq 1 d 1 m3) to 222Rn and 220Rn respectively. & 2012 Elsevier Ltd. All rights reserved.
Keywords: SSNTD Radon dosimetry Passive monitoring Polystyrene films Lexan polycarbonate
1. Introduction In the natural environment, the largest part of radiation dose received by the general public is due to the radon and its progeny (NCRP, 1987). Today, according to the UNSCEAR 1993 the concentrations of radon and its progeny in enclosed spaces may result in significant biological hazards and after smoking it is the most important cause of lung cancer (WHO, 2009). Several passive and active methods have been developed to monitor radon and its daughters (Urban and Piesch, 1981; Nikolaev et al., 1998; Hadler and Paulo, 1994). The choice of particular technique depends on the objective of the study. One of the most important and practical methods for long-time measurements of radon and its progeny in various environmental studies is the use of solid-state nuclear track detectors (Fleischer et al., 1984; Rannou et al., 1986; Sohrabi and Sadeghi, 1991; Hadler et al., 1995; Hadad et al., 2007; Hosseini Pooya et al., 2008). The science of SSNTD was born in 1958 when the first tracks were seen in a crystal of LiF by Young (1958). Fleischer et al.
n
Corresponding author. E-mail address: [email protected] (K. Hadad).
0969-8043/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2012.12.008
(1965) are the pioneers of this field who tried to introduce new applications of track detectors in different areas of science and technologies. Tommasino (1970) and Sohrabi (1974) suggested electrochemical etching method to amplification of the tracks of alpha particles and fission fragments. The track formation properties exist in many materials especially those having long molecules e.g. cellulose nitrates, polyesters or polycarbonates. On the other hand, the basic constructive materials of CD/DVDs, X-ray radiology and MRI films are polycarbonate and polystyrene, respectively. A method based on the absorption ability of some polycarbonate such as Makrofol to measure radon concentration was first employed by Pressyanov et al. (1999) and then developed and expanded by Fleischer (2002) and Tommasino et al. (2009). Radon measurements by CDs/DVDs were first proposed and explored by Pressyanov et al. (2001, 2003). Lexan PCs have been widely used for the indoor radon monitoring around the world and in Iran (Hadad and Doulatdar, 2008; Hadad et al., 2011). The use of CD/DVDs PC for 222Rn mapping has only been reported by Pressyanov (2010) who used the homestored CDs/DVDs in dwellings of three cities in Bulgaria. In this research, we used X-ray radiology and MRI films with polystyrene (PS) base and CD/DVDs with polycarbonate (PC) base for 222Rn and 220Rn dosimetry. The results of dosimetry calibration
K. Hadad et al. / Applied Radiation and Isotopes 74 (2013) 23–25
for 222Rn and 220Rn are presented and their sensitivities are compared. X-ray and MRI PS films are part of many household medical records and are usually kept for many years. Using our technique, such valuable repository of radon concentrations data in dwellings could be utilized for long term of radon monitoring studies.
2. Material and methods 2.1. Calibration sources Five different brands of X-ray radiology and MRI films with polystyrene base PS, and various brands of compact disks were chosen and cut into 2 cm 2 cm size and 2-cm diameter pieces, respectively. The PS radon dosimeters were exposed and calibrated inside a glove-box of 240 l with Uranium ore powder. Uranium ore powder contains natural Uranium which decays to radium and radon in its decay chain. The radon field was calibrated by Lucas scintillation cells calibrated in turn by using a Pylon Standard Source type RN-150 (PYLON Model TH-1025, 1989). Fig. 1 illustrates the calibration source setup (Hosseini Pooya et al., 2008). A powder of gas mantles with activity of 1.65 kBq was used as a 220Rn source. Their thorium activity was determined by gamma spectroscopy method using the 232Th standard source with determined activity (Sadagopan et al., 1997). Gamma spectrometry was carried out using a HPGe detector with a full width at half maximum (FWHM) of 1.88 keV at the 1332 keV g-ray peak of 60 Co and 0.875 keV at the 122 keV g-ray peak of 57Co. The detector was surrounded by a cylindrical heavy lead shield of 10 cm thick and internal layers of cadmium to reduce background radiation originating from building materials and cosmic rays. The HPGe detector was connected to a PC-based multi-channel analyzer for spectrometry analysis. 2.2. Electrochemical etching (ECE) process
MRI PS, X-ray PS and CD/DVD PC samples with etching intervals of 4, 3, 3 h respectively. 2.3. Counting process The images of the etched PS and PC films were obtained by a highresolution scanner (9600 dpi) with a transparency adapter (Umax Scanner Power Look). The number of tracks was counted by image processing software written in MATLAB (Hosseini Pooya et al., 2008). The sensitivities or calibration factors for 222Rn and 220Rn are calculated using the following equation (Urban and Piesch, 1981): NN 0 CF ¼ X 1 ref A 222 Rn or 220Rn, N is the total where X 1 ref is the known activity of number of tracks, N0 is the number of background tracks and A is the sample area.
3. Results and discussion The common etchant in ECE is a simple alkali and its sensitivity could be improved by adding alcohol to the aqueous solution. For the PS samples, we increased the volume ratio to increase the mobility of etchant ions and improve the etchant performance. 7000 6000
Track Density (cm-2)
24
The irradiated sheets were electrochemically etched at room temperature (25–30 1C) with different etching solutions, electric field strengths and time intervals to determine the optimum etching procedure for X-ray and MRI PS samples as well as CD/ DVD thick PCs. The etching solution ‘‘PEMEXs’’ an aqueous solution contained ethanol and 5 M KOH solution with 1:1 volume ratio for the MRI PS films, 9 M KOH solution with 1:1 volume ratio for X-ray PS films and 11 M KOH solution with 1:1 volume ratio for the compact disks. The applied high voltage (HV) was chosen to ensure an effective strength of electric field of 6, 5 and 4 kV/mm for the
5000 4000 3000
Sample 1 Sample 2 Linear Fit
2000 1000 0 0
100
200
Rn222Activity
300
400
500
(KBq-day/cm3)
Fig. 2. Calibration curve of X-ray radiology PS samples.
7000
-2
Track Density (cm )
6000
5000 4000 3000
Sample 1 Sample 2 Linear Fit
2000 1000 0 0
100
200 222
300
400 3
Rn Activity (KBq-day/cm ) Fig. 1. Radon source setup for determination of PS and PC films calibration factors.
Fig. 3. Calibration curve of MRI PS samples.
500
K. Hadad et al. / Applied Radiation and Isotopes 74 (2013) 23–25
Table 1 Results of sensitivity measurements and comparison to other studies. Study
Sensitivity to Rn222 Sensitivity to Rn220 (cm 2 kBq 1 d 1 m3) (cm 2 kBq 1 d 1 m3)
X-ray radiology PS samples 8.77 70.591 CD/DVD PC 0.360 70.090 MRI PS 12.2 71.25 Lexan PC SSNTD 8.5 70.7 (Hosseini Pooya et al., 2008) CDs/DVDs (Pressyanov, 2012; 0.463 70.062 Pressyanov et al., 2010)
0.028 70.006 0.0027 0.0001 0.178 7 0.013 0.018 70.004 0.278
We also increased the effective strength of electric field which allows starting the treeing process immediately following the application of the high voltage. Therefore, the tracks appear in shorter time than the conventional etching methods. The calibration curves of the X-ray and MRI PS samples for 222Rn are presented in Figs. 2 and 3. In both figures, the non-zero value at interception represents the track densities of the control samples due to background activity or inherent defects in PC or PS films. The sensitivities of the PS and CD/DVD PC samples to 222Rn and 220Rn are presented in Table 1. Comparing the sensitivity of our PS samples with previous studies of Lexan PCs (Hosseini Pooya et al., 2008) and CDs/DVD (Pressyanov et al., 2010, Pressyanov, 2012) we could come to the following conclusion: 1. The highest sensitivity to 222Rn and 220Rn is achievable by the MRI PS films (12.271.25 counts/cm 2 kBq 1 d 1 m3). 2. The sensitivity of the X-ray radiology PS films to 222Rn and 220 Rn is comparable with Lexan PC SSNTD (8.7770.591 compared with 8.5 70.7 counts/cm 2 kBq 1 d 1 m3). 3. The compact disks have the lowest sensitivity for 222Rn and 220 Rn. 4. Our results for CD/DVD PC samples are comparable with Pressyanov et al. (2010) results for radon; however, we have achieved faster ECE processing time intervals by optimizing the etching condition. 5. Overall, the samples have higher sensitivity to 222Rn than 220 Rn. The reason behind such phenomena is the longer half life of 222Rn compared with 220Rn. Our result points out the efficient applications of different SSNTD for radon and thoron monitoring purposes. Due to low sensitivity of CDs/DVDs, they are suitable for a high concentration of 222Rn and 220Rn or longer exposure time intervals. Due to their higher sensitivities, the MRI and X-ray PS films are suitable for low radon concentration media or shorter exposure time intervals. The stored MRI or X-ray medical records of people stored in the houses could be readily used for long-term radon and thoron exposure. However, since these records are usually
25
stored inside envelopes, the effect of such packing on radon exposure could be an important issue.
References Fleischer, R.L., Price, P.B., Walker, R.M., 1965. Solid state track detector: application to nuclear science and geophysics. Annu. Rev. Nucl. Sci. 15, 1–28. Fleischer, R.L., Turner, L.G., George, A.C., 1984. Passive measurement of working levels and effective diffusion constants of radon daughters by the nuclear track technique. Health Phys. 47, 9–19. Fleischer, R.L., 2002. Serendipitous radiation monitors. Am. Sci. 90, 324–331. Hadad, K., Doulatdar, R., Mehdizadeh, S., 2007. Indoor radon monitoring in Northern Iran using passive and active measurements. J. Environ. Radioact. 95 (1), 39–52. Hadad, K., Doulatdar, R., 2008. U-series concentration in surface and ground water resources of Ardabil province. Radiat. Protect. Dosimetry 130, 309–318. Hadad, K., Hakimdavoud, M.R., Hashemi Tilehnoee, M., 2011. Indoor radon survey in Shiraz-Iran using developed passive measurement method. Iran. J. Radiat. Res. 9, 175–182. Hadler, J.C., Paulo, S.R., 1994. Indoor radon daughter contamination monitoring: the absolute efficiency of CR-39 taking into account the plate-out effect and environmental conditions. Radiat. Protect. Dosimetry 51, 283–296. Hadler, N.J.C., Iunes, P.J., Paulo, S.R., 1995. A possibility of monitoring indoor radon daughters by using CR-39 as an alpha-spectrometer. Radiat. Meas. 25, 609–610. Hosseini Pooya, S.M., Afarideh, H., Kardan, M.R., Taheri, M., 2008. Design of an alpha spectrometry system for separated measurements of radon/thoron daughters’ concentration by Lexan PC SSNTD. Nucl. Instrum. Methods Phys. Res. 594, 44–49. National Council on Radiation and Protection and measurements, 1987. Ionizing Radiation Exposure of Population of the United States. NCRP Report No. 93. Pressyanov, D., Van Deynse, A., Buysse, J., Poffijn, A., Meesen, G., 1999. Polycarbonates: a new retrospective radon monitor. In: Proceedings of the IRPA Regional Congress on Radiation Protection, Budapest, Hungary. Pressyanov, D., Buysse, J., Van Deynse, A., Poffijn, A., Meesen, G., 2001. Indoor radon detected by compact disks. Nucl. Instrum. Methods 459, 665–666. Pressyanov, D., Buysse, J., Poffijn, A., Meesen, G., Van Deynse, A., 2003. The compact disk as radon detector—a laboratory study of the method. Health Phys. 84, 642–651. Pressyanov, D., Mitev., K., Georgiev., S., Dimitrova, I., 2010. Radon mapping by retrospective measurements—an approach based on CDs/DVDs. J. Environ. Radioact. 101, 821–825. Pressyanov, D., 2012. Retrospective measurements of thoron and radon by CDs/ DVDs: a model approach. Radiat. Protect. Dosimetry 149, 464–468. PYLON Model TH-1025, 1989. Flow Through Thoron Gas Source Instruction Manual, Pylon Electronic Development Company, Canada. Rannou, A., Jeanmaire, L., Tymen, G., Mouden, A., Naour, E., Parmentier, N., Renouard, H., 1986. Use of cellulose nitrate as radon and thoron daughters detectors for indoor measurements. Nucl. Tracks 12, 747–750. Sohrabi, M., 1974. The amplification of Recoil particle tracks in polymers and its application in fast neutron personnel dosimetry. Health Phys. 27, 598–600. Sohrabi, M., Sadeghi, M., 1991. Efficient detection and spectrometry of alphas from radon daughters in polycarbonate. Nucl. Tracks Radiat. Meas. 19, 421–422. Sadagopan, G., Nambi, K.S.V., Venkataraman, G., Sukla, V.K., Kayasth, S., 1997. Estimation of thorium in gas mantles to ascertain regulatory compliance. Radiat. Protect. Dosimetry 71, 53–56. Tommasino, L., 1970. CNCE Report RT/PRO. 71. Tommasino, L., Tommasino, M., Viola, P., 2009. Radon film-badges by solid radiators to complement track detector-based radon monitors. Radiat. Meas. 44, 719–723. Urban, M., Piesch, E., 1981. Low level environmental radon dosimetry with a passive track etch detector device. Radiat. Protect. Dosimetry 1, 97–109. World Health Organization, 2009. WHO Handbook on Indoor Radon. WHO Press, Geneva. Young, D.A., 1958. Etching of radiation damage in lithium fluoride. Nature 185, 375–377.